1 Assessing Concussion Rates and Vestibular Function in Athletes Who Are Deaf Or Hard-Of-Hearing Dissertation Presented in Parti

Home , Balance disorder, Flocculonodular lobe

Assessing Concussion Rates and Vestibular Function in Athletes who are Deaf or Hard-of-Hearing

Dissertation

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

Matthew Paul Brancaleone

Graduate Program in Health and Rehabilitation Science

The Ohio State University

2020

Dissertation Committee

James A. Onate, Advisor

Laura C. Boucher

Daniel M. Merfeld

Jingzhen Yang

Paul Giles

Copyrighted by

Matthew P. Brancaleone

2020

Abstract

There are up to an estimated 3.8 million sport-related concussions per year in the

United States. Currently concussion consensus statements support a multi-faceted assessment approach for the management of concussions, including vestibular assessments. Within the deaf and hard-of-hearing (D/HoH) population, there may be underlying vestibular dysfunction due to the proximity of the vestibular apparatus to the cochlea, including shared neurovascular supply. Specifically, vestibular assessment outcomes of athletes who are D/HoH may not accurately reflect that of available normative data. If these possible discrepancies are not accurately identified, it may negatively influence the diagnosis, injury management, and return-to-play decisions of athletes who are D/HoH. Therefore, the purpose of this research was to assess concussion rates and vestibular function in athletes who are D/HoH.

Aim 1 explored concussion rates in collegiate athletes who are D/HoH. The results of this aim suggest that athletes who are hearing had an increased concussion rate compared to athletes who are D/HoH when looking at all sports combined, football alone, and male athletes alone. No other significant differences regarding concussion rates were identified between groups. Athletes who are D/HoH in sex comparable sports may not have a higher rate of concussion compared to athletes who are hearing.

Aim 2 investigated the effect of hearing status on static and dynamic postural control performance of athletes who are D/HoH and athletes who are hearing. The results of this aim indicate that there are static postural control performance differences between athletes who are D/HoH and athletes who are hearing. Athletes who are D/HoH had greater postural sway during conditions 1, 3, and 4 of the modified Clinical Test of

Sensory Interaction and Balance (mCTSIB) for total, anterior-posterior (AP), and medial- lateral (ML) center-of-pressure (CoP) excursion, 95% ellipse sway, AP and ML range, and ML CoP root-mean-sqaure (RMS). No statistically significant differences in dynamic postural control performance were found between athletes who are D/HoH and athletes who are hearing. Baseline assessments for static postural control performance may be warranted for athletes who are D/HoH rather than comparing to existing normative data.

Aim 3 investigated the effect of hearing status on dynamic visual acuity (DVA) of athletes who are D/HoH and athletes who are hearing. The results suggest that hearing status did not have a significant effect on DVA performance. Additionally, there was no statistically significant DVA performance differences between athletes who are deaf and athletes who are hard-of-hearing. For this assessment, baseline assessments of DVA of athletes who are D/HoH may not be necessary for preseason assessment.

Findings from this study suggest that athletes who are D/HoH experience concussions at a similar rate in sex comparable sports to athletes who are hearing. Due to similar concussion rates and possible underlying vestibular dysfunction, special considerations of vestibular assessment outcomes are crucial for appropriate concussion management, and return-to-sport decisions.

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Dedication

For my wife, Ashley Brancaleone

And my sons, Vincent and Luca Brancaleone

Acknowledgments

I would first like to thank and acknowledge my advisor and mentor, Dr. James

Onate, who guided me throughout this process. I’d also like to thank the rest of my committee, Dr. Laura Boucher, Dr. Daniel Merfeld, Dr. Jingzhen Yang, and Dr. Paul

Giles for their continual guidance throughout this process.

I would also like to thank Dr. Rene Shingles, who has served as a mentor to me since my undergraduate career. You sparked my interest in research and nurtured my intellectual curiosity since day one. My career thus far would not have been possible without your influence and continued support to this day. Fire Up, Chips.

My physical therapy career led me to Columbus, Ohio in 2014, where I have been fortunate enough to work for Ohio State Sports Medicine. I would like to thank my fellow physical therapists, athletic trainers, Ohio State Sports Medicine leadership, and support staff for their understanding and support throughout. Specifically, I’d like to thank Dr. Matt Briggs for giving me an opportunity to become a sports physical therapy resident, which helped lay the foundation for the remainder of my academic career as a student.

I would also like to thank the Gallaudet University athletics staff for their support during the pursuit of my PhD, specifically Mariko Kobanawa and Tom McKnight.

To my fellow lab-mates and other students, both undergraduate and graduate, I could have never have achieve this without you. Thank you Maria Talarico, Dr. Daniel

Clifton, Dr. Michael McNally, Christopher Ballance, Megan Kobel, Mike Lantz, Adam

Throckmorton, Katie Jira, Kayla Berezne, Jake Browner, Derek Cross, Kaylee Karsh,

Caroline Manning, Julie Meyer, Jack Reifenberg, and Bailey Urbach.

Lastly and most importantly, I’d like to thank my entire family. My parents, Paul and Lori Brancaleone. My siblings, Jessica Perry and Steven Brancaleone. My wife,

Ashley Brancaleone. And my two sons, Vincent and Luca Brancaleone. You all are everything to me.

Vita

2017 to present ...... Fixed-Term Faculty Department of Physical Therapy Central Michigan University

2016 to present ...... Staff Physical Therapist Ohio State Sports Medicine The Ohio State University

2016 ...... Sports Certified Specialist American Board of Physical Therapy

2014...... Doctorate of Physical Therapy Central Michigan University

2013 ...... Certified Strength and Conditioning Specialist National Strength and Conditioning Association

2013 ...... Athletic Trainer USA Deaf Sports Federation

2011 ...... Assistant Athletic Trainer Shepherd University

2011 ...... Certified Athletic Trainer Athletic Training Board of Certification

2010...... Athletic Training Intern Gallaudet University

2010 ...... Bachelor of Science in Athletic Training Central Michigan University

2006 ...... Anchor Bay High School New Baltimore, MI

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Publications

Brancaleone MP, Ballance CJ, Clifton DR, Talarico MK, Onate JA. The effectiveness of inertial sensors to assess postural stability in individuals who are concussed: A systematic review. Athl Train Sports Health Care. 2019;11(5):243-248.

Brancaleone MP, Clifton DR, Onate JA, Boucher LC. Concussion risk in athletes who are deaf or hard-of-hearing compared to athletes who are hearing. Clin J Sports Med. 2018.

Brancaleone MP, Shingles RR, DeLellis N. Deaflympian’s satisfaction of athletic training services at the 2013 Deaflympic summer games. J Athl Train. 2017;52(7):708- 718.

Brancaleone MP, Shingles RR. Communication patterns among athletes who are deaf and athletic trainers: a pilot study. Athl Train Sports Health Care. 2015;7(1):29-33.

viii

Fields of Study

Major Field: Health and Rehabilitation Science

Graduate Interdisciplinary Specialization: College and University Teaching

Table of Contents

Abstract ...... ii Dedication ...... iv Acknowledgments...... v Vita ...... vii Publications ...... viii Fields of Study ...... ix Table of Contents ...... x List of Tables ...... xiv List of Figures ...... xv Chapter 1. Aims, Limitations, and Delimitations ...... 1 Aims ...... 2 Operational Definitions ...... 2 Limitations ...... 5 Delimitations ...... 5 Chapter 2: Literature Review ...... 6 Epidemiology Individuals who are Deaf or Hard-of-Hearing ...... 6 Types of Hearing Loss ...... 6 Conducting Research of Individuals who are Deaf or Hard-of-Hearing ...... 7 Athletes who are Deaf or Hard-of-Hearing ...... 8 Vestibular System Anatomy and Physiology ...... 10 Peripheral Vestibular System Overview ...... 10 Vestibular Hair Cells...... 10 Anatomy of the Semicircular Canals ...... 11 Physiology of the Semicircular Canals ...... 13 Anatomy of the Otolith Organs...... 14

Physiology of the Otolith Organs ...... 15 Blood Supply ...... 15 Innervation ...... 16 The Central Vestibular System ...... 17 Postural Control ...... 19 Athletes and Postural Control ...... 20 Postural Control of Individuals who are Deaf or Hard-of-Hearing ...... 21 Vestibular-Ocular Reflex ...... 23 Vestibular-Ocular Reflex and Gymnastics ...... 25 Vestibular-Ocular Reflex and Figure Skating...... 26 Vestibular-Ocular Reflex and Individuals who are Deaf or Hard-of-Hearing ...... 27 Vestibular Dysfunction Following Concussion ...... 28 Chapter 3: Concussion Rates in Athletes who are Deaf or Hard-of-Hearing Compared to Athletes who are Hearing...... 30 Abstract ...... 30 Introduction ...... 32 Methods...... 34 Participants ...... 34 Data Collection ...... 36 Statistical Analysis ...... 36 Results ...... 37 Discussion ...... 43 Conclusion ...... 46 Chapter 4: The Effect of Hearing Status on Static and Dynamic Postural Control Performance of Athletes ...... 47 Abstract ...... 47 Introduction ...... 49 Methods...... 51 Participants ...... 51 Inclusion and Exclusion Criteria ...... 52 Consent and Communication Considerations ...... 52 Questionnaire ...... 53 Static and Dynamic Postural Control Assessments ...... 53 xi

Data Analysis ...... 60 Statistical Analysis ...... 61 Results ...... 63 Static Postural Control Performance and Hearing Status ...... 63 Total Center-of-Pressure Excursion ...... 63 Anterior-Posterior Center-of-Pressure Excursion ...... 66 Medial-Lateral Center-of-Pressure Excursion ...... 69 Anterior-Posterior Center-of-Pressure Range ...... 72 Medial-Lateral Center-of-Pressure Range ...... 75 95% Ellipse Sway Area ...... 78 Anterior-Posterior Center-of-Pressure Root Mean Square ...... 81 Medial-Lateral Center-of-Pressure Root Mean Square ...... 84 Dynamic Postural Control Performance and Hearing Status ...... 87 Time-to-Stability ...... 87 Static Postural Control Performance and Condition ...... 89 Total Center-of-Pressure Excursion ...... 91 Anterior-Posterior Center-of-Pressure Excursion ...... 91 Medial-Lateral Center-of-Pressure Excursion ...... 92 Anterior-Posterior Center-of-Pressure Range ...... 92 Medial-Lateral Center-of-Pressure Range ...... 93 95% Ellipse Sway Area ...... 93 Anterior-Posterior Center-of-Pressure Root Mean Square ...... 94 Medial-Lateral Center-of-Pressure Root Mean Square ...... 94 Static Postural Control Performance Regression Model ...... 95 Total Center-of-Pressure Excursion ...... 97 Anterior-Posterior Center-of-Pressure Excursion ...... 97 Medial-Lateral Center-of-Pressure Excursion ...... 97 Anterior-Posterior Center-of-Pressure Range ...... 98 Medial-Lateral Center-of-Pressure Range ...... 98 95% Ellipse Sway Area ...... 98 Anterior-Posterior Center-of-Pressure Root-Mean-Square ...... 99 Medial-Lateral Center-of-Pressure Root-Mean-Square ...... 99

xii

Discussion ...... 100 Conclusion ...... 105 Chapter 5: Determine the Effect of Hearing Status on Dynamic Visual Acuity Performance of Athletes ...... 106 Abstract ...... 106 Introduction ...... 108 Methods...... 109 Participants ...... 109 Inclusion and Exclusion Criteria ...... 110 Consent and Communication Considerations ...... 110 Questionnaire ...... 111 Dynamic Visual Acuity Assessment ...... 111 Statistical Analysis ...... 112 Result ...... 113 Discussion ...... 120 Conclusion ...... 124 Chapter 6: Conclusion and Future Research Considerations ...... 126 Conclusion ...... 126 Future Directions ...... 128 Bibliography ...... 129 Appendix A. Questionnaire ...... 155

xiii

List of Tables

Table 1. Participant distribution by year and sport ...... 35 Table 2. Injury counts by sport for male and female athletes combined ...... 38 Table 3. Injury counts by sport for male athletes only ...... 40 Table 4. Injury counts by sport for female athletes only ...... 42 Table 5. Sensory system(s) compromised and available for sensory input during each condition of the modified Clinical Test of Sensory Interaction and Balance ...... 55 Table 6. Characteristics of participants ...... 62 Table 7. Total center-of-pressure excursion by demographic ...... 65 Table 8. Anterior-posterior center-of-pressure excursion by demographic ...... 68 Table 9. Medial-lateral center-of-pressure excursion by demographic ...... 71 Table 10. Anterior-posterior center-of-pressure range by demographic ...... 74 Table 11. Medial-lateral center-of-pressure range by demographic ...... 77 Table 12. 95% ellipse sway area by demographic ...... 80 Table 13. Anterior-posterior center-of-pressure root mean square by demographic ...... 83 Table 14. Medial-lateral center-of-pressure root mean square by demographic ...... 86 Table 15. Static postural control performance by condition ...... 90 Table 16. Generalized linear regression results ...... 96 Table 17. Characteristics of participants ...... 114 Table 18. Dynamic Visual Acuity of Athletes who are Hearing and Deaf or Hard-of- Hearing ...... 116 Table 19. Characteristics of deaf and hard-of-hearing participants ...... 118 Table 20. Dynamic Visual Acuity Scores of Athletes who are Deaf and Hard-of-Hearing ...... 119

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List of Figures

Figure 1. Conditions 1 (left) and 3 (right) of the modified Clinical Test of Sensory Interaction and Balance...... 56 Figure 2. Time-to-stability task...... 59 Figure 3. Total center-of-pressure excursion of athletes who are deaf or hard-of-hearing and hearing ...... 64 Figure 4. Anterior-posterior center-of-pressure excursion athletes who are deaf or hard- of-hearing and hearing ...... 67 Figure 5. Medial-lateral center-of-pressure excursion of athletes who are deaf or hard-of- hearing and hearing ...... 70 Figure 6. Anterior-posterior center-of-pressure range of athletes who are deaf or hard-of- hearing and hearing ...... 73 Figure 7. Medial-lateral center-of-pressure range of athletes who are deaf or hard-of- hearing and hearing ...... 76 Figure 8. 95% ellipse sway area of athletes who are deaf or hard-of-hearing and hearing ...... 79 Figure 9. Anterior-posterior center-of-pressure root mean square of athletes who are deaf or hard-of-hearing and hearing ...... 82 Figure 10. Medial-lateral center-of-pressure root mean square of athletes who are deaf or hard-of-hearing and hearing ...... 85 Figure 11. Time-to-stabilityof athletes who are deaf or hard-of-hearing and hearing ...... 88

Chapter 1. Aims, Limitations, and Delimitations

There are an estimated 3.8 million1 sport-related concussions per year in the

United States accounting for 8.9% of high school and 5.8% of collegiate athletic injuries.2

These numbers may be skewed whereby 50% to 75% of high school concussions3-5 and

11.8% of collegiate concussions6 are underreported. Concussions come at a great

financial burden costing society an estimated $76.5 billion in 2010.7 Due to the high

occurrence and economic impact from concussions, appropriate management of this

injury is crucial. Concussion consensus statements support a multi-faceted assessment

approach for the management of concussions, including vestibular assessments.8-10

Symptoms associated with vestibular dysfunction have been reported by over 50% of

athletes who are concussed11 and lead to a 6.4 times greater risk of protracted recovery.12

In the most recent consensus statement on concussion in sport, the authors considered if

special populations, such as those with disabilities, should be managed differently.8

Within the deaf and hard-of-hearing (D/HoH) population, there is a lack of literature regarding concussion assessment. Due to the proximity of the vestibular apparatus to the cochlea including the shared neurovascular supply, individuals who are

D/HoH may exhibit vestibular dysfunction.13 Currently, there are an estimated 692,000

school-aged14 and over 71,000 post-secondary15 students who are D/HoH. Although previous researchers have explored postural control performance of children who are

D/HoH,16-18 there is a lack of information characterizing vestibular function of athletes at

all competition levels who are D/HoH. Our long-term goal is to optimize concussion

management of athletes who are D/HoH. The overall objective of this series of studies is

to gain a better understanding of vestibular function of athletes who are D/HoH. Our

main hypothesis is that some individuals who are D/HoH will demonstrate poorer

vestibular function compared to individuals who are hearing. The rationale behind the

proposed research is to characterize vestibular function of individuals who are D/HoH to

ultimately guide vestibular-related interventions, concussion management, and return-to-

sport guidelines.

Aims

Aim 1: To examine the rate of concussions between athletes who are D/HoH and

athletes who are hearing

Aim 2. Determine the effect of hearing status on static and dynamic postural

control performance of athletes.

Aim 3: Determine the effect of hearing status on dynamic visual acuity (DVA) of

athletes.

Operational Definitions

• Hard-of-hearing: Individual who self-reported as having a mild to moderate degree of

hearing loss.

• Deaf: Individual who self-reported as having a severe to profound degree of hearing

loss.

• Sports-related concussion: A traumatic brain injury induced by biomechanical

forces.8 For aim 1, an athlete was considered to have a sports-related concussion if a

“post-injury 1” Immediate Post-Concussion Assessment and Cognitive Test

(ImPACT) assessment was completed.

• Static postural control assessment: Assessed using the modified Clinical Test of

Sensory Interaction and Balance (mCTSIB)19 on a tri-axial force plate (Bertec

FP4060, Bertec Corp., Columbus, OH, USA). The average of three trials was used to

calculate the static postural control outcome variables including total, anterior-

posterior (AP), and medial-lateral (ML) center-of-pressure (CoP) excursion, AP and

ML CoP range, 95% ellipse sway area, and AP and ML amplitude root-mean square

(RMS).

• Dynamic postural control assessment: Assessed using a single-leg jump-landing

task20 using a tri-axial force plate (Bertec FP4060, Bertec Corp., Columbus, OH,

USA) and a height-measuring device (Vertec, Sports Imports, Columbus, OH, USA).

Time-to-stabilization (TTS) was calculated as the time when the vertical ground

reaction forces reached and stayed within 5% of the participants’ body weight for at

least 500 ms following landing. The average of three trials was used to calculate TTS.

• Baseline visual acuity: Assessed using the Bertec Vision Advantage (Bertec Corp.,

Columbus, OH, USA).21 The participant sat 5 feet away looking straight ahead at the

laptop screen. The letter “E” or optotype flashed on the screen pointed in one of four

directions (up, down, left, or right). The participant identified the direction of the

optotype when it disappeared. If the participant could not identify the direction, they

indicated, “I don’t know.” The optotype grew larger for a wrong answer and smaller

for a correct answer until the software algorithm had determined the participant’s

threshold acuity.

• Visual Processing Time: Assessed using the Bertec Vision Advantage (Bertec Corp.,

Columbus, OH, USA).21 The participant sat 5 feet away looking straight ahead at the

laptop screen. The letter “E” or optotype flashed on the screen pointed in one of four

directions (up, down, left, or right). The participant identified the direction of the

optotype when it disappeared. If the participant could not identify the direction, they

indicated, “I don’t know.” The optotype would stay on screen for less time for correct

answers and more time for correct answers until the software algorithm had

determined the participant’s visual processing time.

• Dynamic visual acuity: Assessed using the Bertec Vision Advantage (Bertec Corp.,

Columbus, OH, USA).21 The participant sat 5 feet away looking straight ahead at the

laptop screen. The participant’s head was passively rotated in yaw at 2 Hz by a

research team member. The letter “E” or optotype flashed on the screen pointed in

one of four directions (up, down, left, or right). The participant identified the

direction of the optotype when it disappeared. If the participant could not identify the

direction, they indicated, “I don’t know.” A wearable, wireless head tracker was worn

by the participant on their forehead that verified the rotation speed by the research

team member and also determine when optotypes were presented on the computer

screen. The optotype grew larger for a wrong answer and smaller for a correct answer

until the software algorithm had determined the participant’s threshold DVA.

Limitations

• Playing time and position played were not collected or included in the analysis

and may have an influence on concussion rate of athletes who are D/HoH.

• Though the number of practices and competitions were similar, athletic skill may

have been inherently different between groups for aims 2 and 3 and influenced

our outcomes.

• Sport was not controlled for during our analysis for aims 2 and 3 due to the high

variability of sport participation by the participants.

Delimitations

• Only collegiate athletes were studied so our findings may not be generalizable to

other competition levels.

• Participants who are D/HoH were recruited from a single institution. This

institution is barrier free for individuals who are D/HoH and therefore may not be

generalizable to other collegiate athletes who are D/HoH

• The level of collegiate athletic competition was different between athletes who

are hearing and athletes who are D/HoH for aims 2 and 3.

• For aims 2 and 3, hearing status was self-reported and thus possibly inaccurate.

• History of cochlear implantation surgery was not controlled for during our

analysis for aims 2 and 3.

Chapter 2: Literature Review

Epidemiology Individuals who are Deaf or Hard-of-Hearing

According to the World Health Organization, there are estimated to be 466

million people world-wide that have disabling hearing loss.22 Within the United States, there are an estimated 28.6 million individuals with an auditory disorder.23,24 It is

reported that 1-6/1000 children are born with some degree of hearing loss in one or both

ears often due to congenital etiology.25,26 However, some types of congenital hearing loss

are not recognized until later in childhood.27 Profound, early onset deafness is apparent in

4-11/10,000 children with about 50% of these being from congenital etiology.28

Additionally, it is estimated that 15% of adults in the United States have difficulty

hearing,29 with men twice as likely than women to have hearing loss between the ages of

20 and 69.30 The percentage of adults with hearing loss increases with age. Two percent

of adults aged 45 to 54, 8.5% of adults aged 55 to 64, 25% of adults aged 65 to 74, and

75% of adults aged 75 or older have some degree of hearing loss.31

Types of Hearing Loss

There are three types of hearing loss: sensorineural, conductive, and mixed.32

Sensorineural hearing loss is characterized by dysfunction of the hair cells within the cochlea and the vestibulocochlear nerve.33 The leading etiologies of sensorineural hearing

loss include inherited genetic disorders, noise exposure, and presbycusis.33 Conductive

hearing loss is characterized as outer ear or middle ear dysfunctions that do not allow for

mechanical vibrations to reach the inner ear.32 Conductive hearing loss etiology includes

cerumen impaction, otitis media, and otosclerosis or other anatomical abnormalities.32,33

Lastly, mixed hearing loss involves a combination of both sensorineural and conductive

hearing loss. Hearing aids are often recommended as treatment for individuals with mild

to moderate hearing loss, while individuals who have profound hearing loss or total

deafness are often eligible for a cochlear implant.34 As of December 2012, there have been an estimated 58,000 cochlear implant implantations performed on adults and 38,000 performed on children in the United States.31 However, there are many individuals who

are deaf that choose to not receive treatment and utilize American Sign Language (ASL)

for their primary mode of communication.35

Conducting Research of Individuals who are Deaf or Hard-of-Hearing

The informed consent process requires prospective research participants to be able to make an informed and voluntary decision to participate in research.36 While traditional practice is to provide informed consent and other related research documents to prospective research participants in written English,36 this may not be appropriate for

individuals who are deaf or hard-of-hearing (D/HoH) due to discrepancies in reading levels between these populations. Informed consents are typically written at a 12th grade reading level, at the minimum.37 The average high school student who is deaf graduates

with approximately a 3rd to 4th grade reading level while the average high school student

who is hard-of-hearing graduates with approximately a 4th to 5th grade reading level.38

These vast differences in graduating high school reading levels between students who are

hearing and those who are D/HoH may present challenges in informed consent and

research participation comprehension. In addition to poor reading levels, only 20% of

individuals who are deaf in the United States have fluency in written English.39 Due to

this potential miscommunication, federal regulations specify that information provided to

prospective research participants be accessible and comprehensible in their preferred

language40 despite their English proficiency.41 Additionally, it is difficult to present

informed consents and data collection processes to prospective research participants

when the research team is not familiar with the prospective research participant’s native

language, cultural norms, and values.41 This may result in mistrust, anxiety, and confusion between the research participant and research team during the informed consent process.36 Therefore, modifications must be made to the informed consent and data collection process in order to optimize clear communication and understanding by the research participants.36 Suggested variations of the informed consent process include

providing the informed consent in an easy-to-read English version as well as in video

form in ASL by a certified ASL interpreter.36 Lastly, mitigating any potential mistrust

and miscommunication between the participants and research team can be accomplished

with the inclusion of research personnel that are fluent in ASL and are familiar with the

cultural norms and values of individuals who are D/HoH.36

Athletes who are Deaf or Hard-of-Hearing

Currently, there are an estimated 692,000 school-aged14 and over 71,00015 postsecondary students who are D/HoH with many participating in athletics. Though many school-aged students who are D/HoH participate in athletics in a mainstream school

8 environment, there are also residential schools for the deaf that have athletic programs in which students who are D/HoH participate.42 Athletes who are D/HoH also participate at the collegiate level nationwide; however, the majority of collegiate athletes who are

D/HoH either participate in athletics at Gallaudet University or Rochester Institute of

Technology (RIT). Gallaudet University is the “only university designed to be barrier- free for deaf and hard-of-hearing students,”43 while RIT houses the National Technical

Institute for the Deaf (NTID) which is the “first and largest technological college in the world for students who are deaf or hard-of-hearing.”44

In addition to school-aged and collegiate athletics for individuals who are D/HoH, there are also international competitions such as the Deaflympics.42 The Deaflympics are an International Olympic Committee recognized competition governed by the

International Committee of Sports for the Deaf (ICSD), which is held every four years for elite athletes who are D/HoH.45 The first Deaflympic summer games were held in Paris,

France in 1924 and the first Deaflympic Winter Games were held in Seefeld, Austria in

1949.46 They are the second longest-running multisport event in the world behind the

Olympics.45 In order to be eligible for participation, the athlete must have a hearing loss of 55 dB pure-tone average in the better ear and are not allowed to wear a cochlear implant or hearing aid during competition.47 During the 2013 Deaflympic Summer

Games in Sofia, Bulgaria, there were 2,711 athletes who are D/HoH from 82 nations that participated while the 2015 Deaflympic Summer Games held in Khanty-Mansiysk,

Russia included 226 athletes who are D/HoH from 27 countries.46

Vestibular System Anatomy and Physiology

Peripheral Vestibular System Overview

The peripheral vestibular system is located within the petrous portion of the

temporal bone and consists of the bony and the membranous labyrinth.48 The bony

labyrinth is filled with perilymph that is rich with sodium while the membranous

labyrinth is filled with endolymph that is rich with potassium.48 Within the membranous

labyrinth of the peripheral vestibular system lie five sensory end organs. These five

sensory organs include the three semicircular canals (horizontal, anterior and posterior)

and two otolith organs (saccule and utricle) and directly synapse with the

vestibulocochlear nerve (cranial nerve VIII).48 Within the semicircular canals and otolith

organs are vestibular sense organs, the cristae ampullae and the maculae, respectfully.48

Essential to the function of the vestibular system, the vestibular hair cells produce the

bioelectric response that communicates directly to the vestibulocochlear nerve.48

Vestibular Hair Cells

Within the peripheral vestibular system, there are two structural types of hair

cells: Type I and Type II.48,49 Type I hair cells have a rounded or globular base and

typically has a single afferent synapse with a nerve-ending called a calyx which surrounds the base of the hair cell.48,50 Type II hair cells are cylindrical in shape and often

have many efferent and afferent nerve endings call boutons.48,50 Hair cells are organized

morphologically throughout the entire cristae ampullari and maculae.48 Type I hair cells

tend to be at the center of the vestibular epithelia while the type II hair cells are

commonly located around the periphery.51 Within the vestibular end organs, type I and

type II have a 1:1 ratio with approximately 23,000 hair cells within the semicircular canal

cristae and approximately 52,000 hair cells in the otolith maculae.52 The hair cells are

topped with approximately 70-100 stereocilia, arranged from tallest to shortest.49,53 Next to the tallest stereocilia is a single, large kinocilium.2 Interconnecting each of the

individual stereocilia and the single kinocilium are elastic tip links.54 The tip links allow

each of the stereocilia and single kinocilium to move together during acceleration and

mechanically open and close ion channels that are thought to sit on top of the

stereocilia.54 Hair cells have a resting potential of about 80 mV54 with a spontaneous

firing rate of the afferent nerve fibers of approximately 100 spikes per second.55 When

stereocilia are tilted toward the kinocilium secondary to head motion, the hair cells are

depolarized, resulting in an increased firing up to 500 spikes per second of the afferent

vestibular nerve.49,53 Conversely, when the stereocillia are bent away from the kinocilium, the hair cells become hyperpolarized, which lead to decreased firing rates of the vestibular nerve.49 The signals are then transferred from the vestibular nerve to the

extraocular nuclei, the spinal cord, or the cerebellum.53

Anatomy of the Semicircular Canals

There are three semicircular canals that respond to angular acceleration:

horizontal, anterior, and posterior.56 Each bony semicircular canal slightly differs in

diameter. The horizontal canal has a diameter of approximately 2.3 mm (SD 0.21), the

anterior canal has a diameter of about 3.2 mm (SD 0.24) and the posterior canal has a

diameter of about 3.1 mm (SD 0.30).54 The diameter of each membranous semicircular

canal is estimated to be between 0.2 and 0.3 mm.57 The orientation of the semicircular

canals allows them to be maximally sensitive to different motions. The horizontal canal is

responsible for primarily for sensing motions in the yaw plane.56 Additionally, the

horizontal semicircular canal is orientated approximately 20-30° upward from the true

horizontal plane which connects the external auditory canal to the floor of the orbit

(Reid’s baseline).58 The three semicircular canals have a mutually perpendicular or orthogonal relationship to each other. 48 However, this orthogonal relationship is not

perfect and therefore, movement in any direction will excite two semicircular canals and

often all three.59

Each of the semicircular canals arch about 240°60 and have both an open end and

a closed ampullar end.48 The open end of each semicircular canals open into the common vestibule that is shared by each canal and allows free low of the endolymph.48 The open

end of the horizontal semicircular canal communicates directly with the vestibule while

the anterior and posterior semicircular canal form a common crus before opening into the

vestibule.48 Opposite to the closed end is the ampulla, which is a bulbous shape.60 The

cupula is located within the ampulla which is composed of both glycoproteins and

proteoglycans51 and has the same density as the endolymph.48 The cupula extends the

entire ampullar lumen.48 Though the cupula traverses the entire ampulla, it is not

structurally attached48 and does not allow fluid to pass through due to cellular turgor

pressure.50 Forming the floor of the ampulla is the crista ampullaris.48 The crista

ampullaris contains the neurosensory epithelium, which contains the sensory hair cells

that are described above.48 The hair cells project through the cuticular plate and into the

cupula.48

Physiology of the Semicircular Canals

Due to inertia, the endolymph moves with respect to the head during head angular accelerations.48 Hence, angular accelerations yield a relative movement of endolymph in

the semicircular canals61 causing a deflection of the cupula that is approximately

proportional to the angular velocity.54 The cupula acts as a communicator between force

produced via angular acceleration of the head and the hair cells.51 When the cupula is deflected, the sensory hair cells previously mentioned will either increase or decrease their firing rate by depolarizing or hyperpolarizing the afferent nerves depending on the orientation of the hair cell deflection.62 The hair cells in the horizontal semicircular canals

are oriented in a manner that when endolymph flows towards the ampulla or

ampullopetal, excitation occurs.62 Conversely, the hair cells in the anterior and posterior semicircular canals are oriented in a manner that when endolymph flows away from the ampulla or ampullofugal motion, excitation occurs.62 This orientation of the hair cells is referred to as morphologic polarization.63 The vestibular afferent nerve fibers then send

information to the vestibular nuclear cortex within the central nervous system that is

discussed later.54

It should be noted that the semicircular canals are paired secondary to their

coplanar relationship.61 The pairs are as follows: 1) right and left horizontal semicircular

canals, 2) right anterior and left posterior (RALP) semicircular canals, and 3) left anterior

and right posterior semicircular canals (LARP).54 These semicircular canal pairs allow

the central nervous system to receive similar information from two separate sources and

therefore still provides motion information if there is isolated damage to any single

semicircular canal or isolated damage to the canals of a single ear.

Anatomy of the Otolith Organs

There are two otolith organs that sense linear acceleration: utricle and saccule.48

The utricle is located directly posterior to the eyes while the saccule is located posterior

to the maxillary sinuses.48 The macula of the utricle is oriented in the horizontal plane

while the macula of the saccule is located within the sagittal plane and therefore, these

organs have an orthogonal relationship.48 Though the otolith organs are positioned

approximately 90° from one another,48 each is curved-shaped which allows each organ to be sensitive to all gravitational and inertial forces (e.g., gravitational, linear acceleration, tangential acceleration, and centripetal acceleration).64 The utricle is an elliptically

shaped sac that is tilted backwards and downwards approximately 30° and laterally

approximately 10°.48 Due to the utricles’ horizontal orientation, they detect head tilt,

horizontal head acceleration and side-to-side head acceleration.52 The saccule, however,

is a flattened sac that lies in the sagittal plane that is deflected about 18° laterally.65 Due

to the saccule’s vertical orientation, it detects to the omnipresent presence of gravity,

craniocaudal motion of the head and vertical acceleration of the head.48

Similar to the semicircular canals, the sensory hair cells are present in the otolith

organs.54 The hair cells project into the gelatinous material.54 Atop of the gelatinous

material lay the calcium carbonate crystals, or otoconia, that provide the otolith organs

with an inertial mass.54 These otoconia have a specific mass of 2.95 g/cm3 and a diameter

varying between 3 and 30 µm.54

The middle of the surface of the utricle and saccule is represented by the striola.

Within the utricle, the kinocilia are oriented towards the striola.54 Towards the striola of the utricle, the membrane is thin and the hair cells have relatively short cilia.54 Within the saccule, the kinocilia are oriented away from the striola. Towards the striola of the saccule, the membrane is thicker and the hair cells have relatively long cilia.54

Physiology of the Otolith Organs

The otolith organs are sensitive to linear acceleration and gravity.54 When the head moves, the otoconia atop the membrane will lag behind and cause deflection of the hair cells. Depending on the orientation of the hair cells, it will either cause depolarization or hyperpolarization of the hair cells.54 Similar to the semicircular canals, if the hair cell displacement is towards the kinocilia, depolarization occurs; if hair displacement is away from the kinocilia, hyperpolarization occurs.56 Once stimulated, the hair cells will communicate with the afferent vestibular nerve fibers and send information to the vestibular nuclear cortex within the central nervous system.54

Blood Supply

The labyrinthine artery supplies the inner ear structures and neural structures with its blood supply.51 The labyrinthine artery most often originates from the anterior inferior cerebellar artery but sometimes will originate from the basilar artery.51 Following entrance into the inner ear, the labyrinthine artery branches into the anterior vestibular artery and the common cochlear artery.51 The anterior vestibular artery supplies the utricle, horizontal semicircular canal, the ampulla anterior semicircular canal and a small portion of the saccule.51 The common cochlear artery branches into the posterior

vestibular artery and the main cochlear artery.51 The posterior vestibular artery supplies

the inferior portion of the saccule, and the ampulla of the posterior semicircular canal.51

The main cochlear artery supplies the spiral ganglion, organ of Corti, and stria

vascularis.51

Blood is taken away from the utricle, ampulla of the anterior semicircular canal,

and the posterior semicircular canal via the anterior vestibular vein while the posterior

vestibular vein drains the saccule, the ampulla of the posterior semicircular canal, and the

base of the cochlea.51 These two veins, along with the vein of the round window, become

the vestibulocochelar vein.51 The vestibulocochlear vein and the common modiolar vein,

which primarily drains the cochlea, become the vein at the cochlear aqueduct and then

will drain into the petrosal sinus.51 Specifically, the semicircular canals are drained by

veins that form the vestibular aqueduct, which drains into the lateral venous sinus. 51

Innervation

The afferent and the efferent vestibular and cochlear nerve fibers pass through the

lamina cribrosa to make contact with the sensory organs located in the inner ear.51 The

auditory nerve consists of about 30,000 afferent and efferent fibers while the vestibular

nerve consists of about 15,000-25,000 afferent and efferent fibers.51 Scarpa’s ganglion or

the bipolar ganglion cells of the vestibular nerve are arranged in a vertical column.51 The

superior group of the vertical column forms the superior division and innervates the

cristae of the anterior semicircular canal, horizontal semicircular canal, the macule of the

utricle, and the anterio-superior aspect of the saccular maccule.51 The inferior group of the vertical column innervates the crista of the posterior semicircular canal and the main

aspect of the macule of the saccule of the vestibular nerve while the inferior group forms

the inferior division.51

The Central Vestibular System

The central vestibular system is largely made up of the vestibular nuclear cortex,

six pathways, and the vestibulocerebellum.49,53 The six pathways are the medial

longitudinal fasciculus, vestibulospinal tracts, vestibulocolic pathways,

vestibulothalamocortical pathways, vestibulocerebellar pathways, and vestibuloreticular

pathways.53

The vestibular nuclear cortex is the main processor of vestibular input and is

made up of four nuclei: superior, inferior, medial, and lateral.49 The nuclei are located

near the fourth ventricle, at the junction of the pons and the medulla in two major

columns.49,53 The medial vestibular nucleus is located in the medial column and is

responsible for receiving information from the semicircular canals and transmitting it to

the extraocular nuclei via the medial longitudinal fasciculus pathway.49 The medial

nucleus also plays a role in controlling the vestibulospinal reflex.49 The lateral column

consists of the superior, inferior, and lateral vestibular nuclei. The superior vestibular

nucleus receives afferent signals from the superior and posterior semicircular canals, and

like the medial vestibular nucleus, sends efferent signals to the extraocular nuclei.53 Both

superior and medial vestibular nuclei are important in coordination of the vestibulo-

ocular reflex (VOR).49 The lateral vestibular nucleus receives information from the crista

ampularis, the maculae, and the vestibulocerebellum.53 The efferent projections from this nuclei play a role in the function of the lateral vestibulospinal tract. Lastly, the inferior

vestibular nucleus receives afferent information from the maculae of the otolith organs

and has efferent projection to the cerebellum and the other three vestibular nuclei.49,53

The medial longitudinal fasciculus serves to connect the medial vestibular nuclei

to the extraocular nuclei (cranial nerves III, IV, and VI) and the superior colliculus, and is

responsible for influencing eye and head movements.49,53 The vestibulospinal tracts

consist of the lateral vestibulospinal tract, which runs from the lateral vestibular nucleus to lower motor neurons in the limbs and trunk, and the medial vestibulospinal tract which projects from the medial vestibular nucleus to the cervical spinal cord.53 The

vestibulospinal tracts are important for maintaining balance and posture reflexively and

coordination of head and neck movement.49,53 The vestibulocolic pathways project from

the vestibular nuclei to the nucleus of the spinal accessory nerve (cranial nerve XI), and

play a role in influencing head position.3 The vestibulothalamocortical pathways run to

the thalamus and are responsible for relaying information associated with spatial

awareness (i.e. perception of body orientation).53 The vestibulocerebellar pathways run to

the vestibulocerebellum, and help to modulate the response to vestibular information,

including response to the VOR.53 Lastly, the vestibuloreticular pathways run to the reticular formation.53 Their function is to send information to the reticular spinal tract,

which influences postural control and locomotion, and the autonomic centers for nausea

and vomiting.49,53

The vestibulocerebellum is one of three functional divisions of the cerebellum.53

This functional division is made up of the flocculonodular lobe and the vermian cortex of

the cerebellum.49 It is primarily responsible for receiving vestibular information and

utilizing this information to influence eye movements and postural control.49,53 The

majority of the body’s reflexive response to positional changes relies on the

vestibulocerebellum to process the vestibular and visual information received.49,53

Postural Control

Postural control can be defined as the “act of maintaining, achieving, or restoring

a state of balance during any posture or activity.”66 Traditionally, it was thought that

postural control was maintained by stretch reflexes through sensory feedback from the

visual, somatosensory, and vestibular systems.67 Postural control strategies include

compensatory, anticipatory, or a combination of both.68 These strategies have been thought of as reflex-like responses through stimuli of the visual, somatosensory, and vestibular systems.66 A compensatory strategy involves movement or muscular responses

following an unexpected perturbation whereas an anticipatory strategy involves a

voluntary movement or increase in muscular activation in expectation of a perturbation.66

More recently, postural control is now considered to be maintained by the assessment and

control of numerous variables by the central nervous system (CNS).67 These motor skills

can be learned by the CNS and can be trained to be more effective and efficient.66

Clinically, there are numerous ways to assess postural control. These assessments

can provide performance information to a clinician on a specific aspect of postural

control.66 Postural control assessments may assess one’s ability to maintain posture,19

restore posture after an expected69 or unexpected70 perturbation, or achieve a new posture. Each of these options are thought to be valid assessments of postural control but the chosen clinical assessment should be applicable to that patient.66

Athletes and Postural Control

Postural skills are fundamental to athletic performance.71 Previous authors have

demonstrated that athletes demonstrate less sway compared to non-athletes.72

Additionally, athletes who participate in contact sports (e.g. soccer) were found to have decreased postural sway compared to athletes who participate in limited contact sports or who do not participate in sport due to potential increased use of both somatosensory and

vestibular stimuli.73 Within the athlete population, those athletes who typically train on

unstable surfaces were found to have unique postural control strategies compared to

athletes who train on stable surfaces.74 Depending on the sporting discipline, athletes will

need to learn how to maintain postural control on varying types of surfaces (e.g. firm,

foam, and water).75

This finding is supported by numerous studies on postural control performance

with gymnastics.76-82 Gymnasts have been found to have less sway compared to soccer

athletes, swimmers, recreational athletes and basketball athletes.72,83 Though no

differences in postural control performance have been found during a standard upright

position between athletes and physically active individuals, during more challenging

postural control tasks such as standing on a narrow area of support, gymnasts and ice

hockey athletes were found to have less sway compared to other athletes and physical

active individuals.83

While examining athletes who are successful and not successful with competition,

authors found that those who are successful with competition are more stable during both

ecological and non-ecological postural control tasks.84 Ecological postural control

conditions can be thought of those that are evaluated during practice or during a specific

motor skill (e.g. handstand by gymnasts), while non-ecological postural control

conditions are those decontextualized from requirements of that sport (e.g. double-limb static stance).84

Variables that can influence postural control performance of athletes include both

footwear and the type of footwear due to somatosensory feedback from the feet.85,86

Previous authors have investigated the influence of footwear on postural control in

regards to preventing injuries in athletes.71,87 When barefoot, distance runners were found

to have increased postural sway compared to when wearing minimalist, cushioned

ultraflexible shoes or standard running shoes during single-leg stance.87 For the same

cohort, during a jump-landing stabilization assessment, no differences in postural control

performance were found between shoe-type.87

Postural Control of Individuals who are Deaf or Hard-of-Hearing

It is estimated that 18% to 82% of children who are D/HoH have vestibular dysfunction.88-90 Numerous studies have investigated children who are D/HoH and their postural control ability compared to children who are hearing.91-96 Findings from these

studies share similar conclusions that children with sensorineural hearing loss of varying

degrees demonstrate, on average, poorer static postural control ability compared to

children who are hearing.13,91-96 These studies used various types of postural control

assessments including the Sensory Organization test (SOT),13,91 the pediatric Clinical

Test of Sensory Interaction and Balance (pCTSIB),92 double-legged stance with and without foam,93 modified Clinical Test of Sensory Interaction and Balance (mCTSIB),94

the Standing Balance subtests of the Southern California Sensory Integration test,95 and the Balance Error Scoring System.96 Similar results have also been found for adolescents

and adults who are D/HoH.13,97-99 For children, adolescents, and adults who are D/HoH,

there has been conflicting evidence whether the degree of hearing loss or etiology of

deafness has an effect on postural control performance; however, sex does not seem to

have an effect on postural control performance in children who are D/HoH.13,97

Additionally, individuals with profound hearing loss will often receive a cochlear

implant in order to facilitate hearing. A cochlear implant is a device specifically designed

to bypass the inner ear hair cells and to mimic the functions of the cochlea by stimulating

surviving neurons.100 It is estimated that up to 75% of individuals who undergo a

cochlear implant surgery experience post-operative vestibular symptoms.101-107 Though

there is a high percentage of individuals who have vestibular dysfunction following

cochlear implant surgery, static postural control improvement has been seen in

individuals up to two years following cochlear implantation using computerized dynamic

posturography (CDP).106,108 Researchers suggest that this improvement is due to

vestibular compensation.106 Additionally, static postural control deficits have been found

to persist in individuals up to five years follow cochlear implant surgery using the

mCTSIB,109 while dynamic postural control deficits have been found to persist up to one

year following cochlear implantation compared to individuals who are hearing using a

moving platform with eyes open and eyes closed110 and the mCTSIB.111

The current literature on postural control for athletes who are D/HoH is limited to

three peer-reviewed articles. Jin et al.112 compared static postural control performance of 22

those with congenital profound sensorineural hearing loss during the Romberg postural

control task, to that of hearing controls. The results suggest that there are no differences

between athletes who are deaf and hearing controls.112 Eliö z et al.113 and Güzel et al.114

both examined elite soccer players who are D/HoH using the flamingo balance test113

and bilateral and single-limb stance with eyes open on a firm surface.114 Eliö z et al.113

results suggest that soccer players who are D/HoH required more attempts to balance

during the flamingo balance test compared to sedentary individuals who are D/HoH.

Additionally, soccer players who are hearing required more attempts to balance during

the flamingo balance test compared to soccer players who are D/HoH.113 Güzel et al.114 results suggest that non-athletes who are hearing had less medial-lateral sway during single-leg stance on their dominant leg compared to non-athletes who are deaf.

Additionally, soccer players who are D/HoH had less medial-lateral sway during single-

leg stance on their non-dominant leg compared to non-athletes who are D/HoH.114

Vestibular-Ocular Reflex

The purpose of the VOR is coordination of eye movements to allow for clear

vision during head movements.49,53,56 The anatomical composition of the VOR includes

the semicircular canals, the nuclei and neural tracts, and the extraocular muscles.53 The

VOR pathway can be divided into a three-neuron reflex arc 1) a primary sensory afferent

neuron in the Scarpa’s ganglion; 2) a vestibular nucleus neuron, and 3) an oculomotor

neuron.56,115 The pathway itself can be subdivided three major processes 1) detection of

head rotation; 2) inhibition and excitation of extraocular muscles; and 3) eye movements

to compensate for the associated head movement.49 There are six muscles that contribute 23

to eye movements, including the medial and lateral rectus for horizontal movements, the

superior and inferior rectus muscles for vertical movements with a small contribution to

torsional movements, and the superior and inferior oblique muscles responsible for

torsional movements with a contribution to vertical movements.116

The most commonly discussed VOR pathway involves the horizontal SCCs and is

activated with a left or right directional head turn. In response to the head turn,

endolymph is displaced in both right and left horizontal semicircular ducts, deflecting the

cupula to the opposite direction of the head turn.49,53 Deflection of the cupula causes

hyperpolarization of the hair cells in the horizontal canal contralateral to the head turn

and depolarization of the hair cells in the ipsilateral horizontal canal.53 This then causes

excitation of the ipsilateral superior and medial vestibular nuclei, and inhibition of the

contralateral superior and medial vestibular nuclei.49,53 Impulses travel along the medial

longitudinal fasciculus to the oculomotor nuclei ipsilateral to the direction of the head

turn.49 Simultaneously, impulses travel along the ascending tract of Deiters to the contralateral abducens nuclei.49 Stimulation of the ipsilateral oculomotor nuclei and

contralateral abducens nuclei cause contraction of the medial rectus muscle of the

ipsilateral eye and lateral rectus muscle of the contralateral eye, respectively.53 The result

is eye movement to the opposite direction of the head turn.

Similarly, the vertical VOR pathway involves the anterior and posterior SCCs,

which is activated by flexion or extension of the head. In response to head extension, the

posterior canal is stimulated, while the anterior canal is stimulated in response to head

flexion.53 As before, the endolymph deflects the cupula in the opposite direction of the

movement, causing hyperpolarization of the hair cells in the respective SCC.116 This

causes excitation of the superior and medial vestibular nuclei, which then synapses on the

oculomotor and trochlear nuclei during head extension or the oculomotor nucleus during

head flexion.53 In response to head extension, the oculomotor and trochlear nuclei

activate the ipsilateral superior oblique and the contralateral inferior rectus muscles to

allow for downward movement of the eyes.53 In response to head flexion, the oculomotor nucleus activates the ipsilateral superior rectus and the contralateral inferior oblique muscles to allow for upward movement of the eyes.53

When the head and eyes move together to track an object, suppression of the

VOR must occur in order to maintain focus on the target. This is done via the optokinetic

system, which allows for gaze stability during sustained head movements.53 Dysfunction

of suppression of the VOR is associated with slower recovery from concussion

symptoms.116

Athletes and Vestibular-Ocular Reflex

For athletes involved in sports that involve rotational components and high

velocities, the function of the VOR is an essential component to their performance.

Vestibular-Ocular Reflex and Gymnastics

The sport of gymnastics requires athletes to perform a variety of skills involving

flipping and twisting at high velocities. These movements require athletes to rely on

information from several systems, including the vestibular system and more specifically

the VOR. It has been reported that the VOR reduces the ability of gymnasts to locate the

ground during rotational components of their sport, thus requiring them to suppress the

VOR in order for them to view their landing.117

One study examined ten female gymnasts and their ability to suppress the

VOR.117 VOR gain can be defined as the ratio of head velocity to eye velocity.117 Under

ideal conditions, the VOR gain is a 1:1 ratio (i.e. for every degree per second the head turns one way, the eyes turn the same degree per second in the opposite direction).116

While not statistically significant, the results revealed interesting trends among data,

including that higher level or elite gymnasts VOR and VOR cancellation gains.117 This

suggests that these gymnasts would have an advantage when performing skills that

require visualization of the landing.117 While this study did show interesting trends in

regards to the data explored, it should be noted that small sample size and lack of control

subjects make it difficult to draw conclusions from this study.117

Davlin et al.118 examined the relationship between various visual conditions and a

back tuck somersault in female gymnasts. The researchers found that despite

manipulation of vision during back suck somersaults, joint angles, angular velocities, and

timing all remained similar. However, it should also be noted that landing balance was

improved with the presence of vision.118 It is recommended that future studies examine

the kinematics of the end of the somersault under various visual conditions.118

Vestibular-Ocular Reflex and Figure Skating

The sport of figure skating involves athletes performing rotational movements and

jumps at a high velocity on ice that requires a high degree of postural and visual control

to maintain balance. Tanguy et al.119 found that when compared to healthy controls,

figure skaters had a decrease in VOR gain, as well as reduced sensitivity to motion

sickness. This study suggests that figure skaters show signs of vestibular habituation,

allowing them to utilize vestibular information efficiently to prevent them from being

subject to dizziness following multiple rotations on ice.119 Vestibular habituation can be

defined as a decrease in VOR gain due to repeated vestibular stimulations, which differs

from VOR suppression, the ability to perform a head turn that does not result in eye

movements to stabilize gaze.117,119 Another study investigated vestibular-ocular adaptation and its relationship to either age or figure skating discipline (e.g. singles, pairs, dance, or synchronized skating).120 The results of the study found vestibular adaptation

depends on discipline rather than age/experience.120

Vestibular-Ocular Reflex and Individuals who are Deaf or Hard-of-Hearing

The VOR can be assessed various ways but the assessment of dynamic visual

acuity (DVA) is an indirect indicator of VOR function.121 DVA is an individual’s ability

to see clearly while moving.121 Investigation of DVA within the D/HoH population is

limited. The existing literature has investigated DVA in both children122 and adults who are D/HoH.123 Martin et al.122 investigated children between the ages of 4 and 14 years of

age who are D/HoH. The findings of this study suggest that 15.6% of children with

sensorineural hearing loss have reduced DVA.122 Nakajima et al.123 investigated the DVA

of Deaflympic athletes. Their findings suggest the Deaflympic athletes have superior

DVA compared to athletes who are hearing.123 Nakajima et al.123 further suggest that the

enhanced visual function of athletes who are D/HoH may act to support their vestibular

function.

Vestibular Dysfunction Following Concussion

Symptoms associated with vestibular dysfunction, such as dizziness, have been reported in 23% to 81% of athletes within days following concussion.124 Vestibular

dysfunction following a concussion has been found to lead to a 6.4 greater risk of

protracted recovery,11 especially in children with a history of concussion.125 Vestibular

dysfunction following concussion has been found through postural control deficits126-128 and VOR deficits.129 Postural control assessments following concussion include both

non-instrumented and instrumented methods. The most common clinical assessment is

the modified Balance Error Scoring System (mBESS), which is included in the Sideline

Concussion Assessment Tool.8 Previous authors have reported that athletes show a

decrease in mBESS scores following a concussion compared to baseline scores.130

Another postural control assessment includes the SOT. The SOT is an instrumented

postural control assessment on the NeuroCom International Smart Balance Master

System that measures the patient’s ability to maintain a quiet stance while altering the

sensory cues available to them including the visual, vestibular, and somatosensory

systems.70 Vestibular deficits associated with postural control have been found to resolve

in three to five days for clinical assessments131 and up to 14 days for instrumented

assessments.132 However, prolonged dizziness symptoms have continued to be reported

with wide variation from 1.2% of individuals at six months to 32.5% of individuals at

five years following concussion.133-136

Similar to postural control assessments, both non-instrumented137 and

instrumented138,139 VOR assessments exist. Non-instrumented VOR assessments include

the Vestibular-Ocular Motor Screen (VOMS). The VOMS was developed and validated

through the University of Pittsburgh140 and has been used to predict delay in concussion

recovery.141 Symptoms associated with the VOMS typically resolve within one to three weeks142 following concussion.142 Instrumented VOR assessments include the DVA,

which also includes visual functions (as highlighted above) and video head impulse test.

DVA deficits have been found following concussion and typically recover within one

month of concussion.143 Additionally, the video head impulse test has been implemented

on children and adults with concussion with no semicircular canal weakness noted.144

Athletes have been found to have an increased likelihood of VOR deficits if they are

female, have a history of depression, have post-traumatic amnesia, dizziness, blurred vision, or difficulty focusing at the time of concussion129

Chapter 3: Concussion Rates in Athletes who are Deaf or Hard-of-Hearing Compared to Athletes who are Hearing

Abstract

Background: Individuals who are deaf or hard-of-hearing (D/HoH) participate in all levels of collegiate interscholastic athletics. Despite the known involvement of athletes who are D/oH in collegiate athletics, no evidence exists regarding epidemiology of concussion in this population.

Purpose: To compare the epidemiology of concussion between athletes who are

(D/HoH) and athletes who are hearing.

Methods: Data were collected from two Division III athletic programs. One institution is the world’s only university designed to be barrier-free for students who are D/HoH. Six hundred and ninety-three athletes who are D/HoH and 1284 athletes who are hearing were included in this study. Athletes participated in collegiate athletics during the 2012-

2013 to the 2016-2017 academic years. Concussion data were provided by the athletic training staff at each institution. Concussion counts, concussion rate, and injury rate ratios (IRR) with 95% confidence intervals (95%CI).

Results: Thirty athletes who are D/HoH and 104 athletes who are hearing suffered concussions. Athletes who are hearing had an increased injury rate compared to athletes who are D/HoH for all sports combined (IRR=1.87, 95%CI: 1.26, 2.78). Football athletes

30 who are hearing also had an increased injury rate compared to football athletes who are

D/HoH (IRR=3.30, 95%CI: 1.71, 6.37). Concussion rate was higher for male athletes who are hearing than male athletes who are D/HoH (IRR=2.84, 95%CI: 1.62, 4.97). No other significant differences regarding concussion risk were identified.

Conclusion: Athletes who are D/HoH in sex comparable sports may not have a higher rate of concussion than athletes who are hearing. Rate of concussion in football may be greater among athletes who are hearing compared to athletes who are D/HoH.

Introduction

Concussions are common occurrences within athletic environments, with an

estimated 1.6 to 3.8 million sports-related concussions occurring in the United States annually.1 A concussion is defined as a traumatic brain injury induced by biomechanical

forces.8 Specifically, in the collegiate athletic population, concussions represent 5.8% of

all athletic injuries.2 Despite the prevalence of research evaluating concussion incidence

in collegiate athletes, no studies have examined concussion incidence in specific groups

of collegiate athletes who are deaf or hard-of-hearing (D/HoH).

Though the exact number of collegiate athletes who are D/HoH is unknown, there are an estimated 71,000 collegiate students who are D/HoH within the United States.15

Athletes who are D/HoH participate at all competition levels including intercollegiate

athletics.145 Gallaudet University and the National Technical Institute for the Deaf both

are institutions that specialize in educating individuals who are D/HoH.146 Both of these

institutions have National Collegiate Athletic Association (NCAA) Division III athletic

programs where athletes who are D/HoH participate.

Before understanding why concussion rate may differ between athletes who are

D/HoH and athletes who are hearing, it is important to understand the different types of

hearing loss: sensorineural, conductive, and mixed. Sensorineural hearing loss is

characterized by combined damage or deficit to the cochlear hair cell function of the

inner ear and the vestibulocochlear nerve.32 Inherited disorders, noise exposure, and

presbycusis are the leading causes of sensorineural hearing loss.33 Conductive hearing

loss is characterized as outer ear or middle ear disturbances that do not allow for

mechanical vibrations to reach the inner ear.32 The etiology of conductive hearing loss includes cerumen impaction, otitis media, and otosclerosis or other anatomical abnormalities.32,33 Lastly, mixed hearing loss involves a combination of both

sensorineural and conductive hearing loss. Hearing aids are often recommended as

treatment for individuals with mild to moderate hearing loss, while individuals who have

profound hearing loss or total deafness are often eligible for a cochlear implant.34

However, there are many individuals who are deaf that choose to not receive treatment

and utilize American Sign Language (ASL) for their primary mode of communication.35

In addition to differences in hearing, individuals who are D/HoH have also been

found to have other sensory differences. Numerous studies suggest vestibular dysfunction

differences exist within individuals who are D/HoH.13,98,147-151 This is thought to be due

to the close proximity of the cochlea and the vestibular apparatus.13 Additionally,

individuals who are D/HoH that use ASL have been found to have differences in vision

that is thought to be influenced by the visuospatial nature of using a signed language.152

Researchers suggest that individuals who are deaf demonstrate improved peripheral

visual field performance152-158 and similar155,159,160 or worse156,161 central visual field

performance compared to individuals who are hearing. The improved peripheral visual

field performance may allow athletes who are D/HoH to react faster to protect themselves

from potential concussive impacts, however, how these sensory differences influence

concussion rates in this population is unknown.

Given these differences in individuals who are D/HoH, their rate of concussion

may be inherently different compared to athletes who are hearing. Additionally, these

differences may influence the diagnosis and management of a concussion in athletes who

are D/HoH. Therefore, the purpose of this study is to examine the epidemiology of

concussion in athletes who are D/HoH. To achieve this, concussion incidence will be

compared by sport and sex between athletes who are D/HoH and athletes who are

hearing. We hypothesize that athletes who are hearing will demonstrate an increase in

concussion rate compared to athletes who are D/HoH.

Methods

Participants

A sample of convenience consisting of two NCAA Division III athletic programs

was utilized for this study. One of these institutions is the world’s only university

designed to be barrier-free for students who are D/HoH. Athletes who participated in

collegiate varsity football, soccer, basketball, baseball, or softball during the 2012-2013

through the 2016-2017 academic years were included in this study (Table 1). The

percentage of our sample of athletes who are D/HoH who have sensorineural, conductive,

or mixed hearing loss was not known.

Table 1 . Participant distribution by year and sport 2012-2013 2013-2014 2014-2015 2015-2016 2016-2017 Deaf/Hard-of-Hearing Baseball 20 20 14 15 18 Men’s Basketball 12 10 15 14 15 Football 57 54 53 51 61 Men’s Soccer 20 0 0 17 21 Women’s Basketball 12 8 13 13 12 Women’s Soccer 16 15 16 17 14 Softball 16 14 15 11 14 Hearing Baseball 41 50 48 46 43 Men’s Basketball 23 18 15 17 16 Football 105 89 98 88 72 Men’s Soccer 35 39 39 31 30 Women’s Basketball 14 16 19 17 15 Women’s Soccer 28 35 31 30 28 Softball 19 23 23 22 21 Note: Values are counts

Data Collection

The total numbers of athletes included in this study were gathered and tabulated

from each institution’s publically available athletic rosters. De-identified concussion data were collected from the Immediate Post-Concussion Assessment and Cognitive Test

(ImPACT) (ImPACT Applications, Inc., San Diego, CA). These records were provided by the athletic training staff at each institution. Both institutions included in this study had a policy in place that required athletes with a diagnosis of a concussion to have post-

injury neurocognitive assessment via ImPACT. Therefore, an athlete was considered to have a concussion if a “post-injury 1” ImPACT assessment was completed. Each individual who suffered a concussion was counted once whether they suffered more than one concussion or not. This study protocol was approved by The Ohio State University

Institutional Review Board.

Statistical Analysis

Concussion rate was calculated by school and sex for each sport individually, all

sports combined, and sex comparable sports combined (i.e. soccer, basketball, baseball,

and softball). Injury rate ratios (IRR) with 95% confidence intervals (CI) were used to

compare concussion rate between athletes who are D/HoH and athletes who are hearing

for all sports combined, football, and sex comparable sports. IRR with 95% CI were also

used to compare concussion rate between athletes who are D/HoH and athletes who are

hearing for each sport by sex. IRR with 95% CI not including 1.00 were considered

36 statistically significant. Injury rate and IRR were not calculated when injury counts were less than 5. Due to the retrospective nature of this study, playing time was not controlled.

Results

This study included 693 athletes who are D/HoH and 1284 athletes who are hearing. Counts and rate of concussion in all sports and sex comparable sports are presented in Table 2. A total of 30 athletes who are D/HoH (14 males, age = 20.29±2.13, yrs., 16 females, age = 19.75±1.81 yrs.) and 104 athletes who are hearing (77 males, age

= 19.27±1.11 yrs., 27 females, age = 19.48±1.18 yrs.) suffered concussions during the study period. For all sports combined, athletes who are hearing had an increased concussion rate compared to athletes who are D/HoH (IRR=1.87, 95% CI: 1.26, 2.78).

No difference in concussion rate was found between athletes who are D/HoH and athletes who are hearing when examining sex comparable sports.

Table 2. Injury counts by sport for male and female athletes combined Total Injury Counts Injury Rate (95%CI) IRR (95%CI)b Athletes All Sports Deaf/Hard-of-Hearing 30 693 4.33 (2.78, 5.88) - Hearing 104 1284 8.1 (6.54, 9.66) 1.87 (1.26, 2.78)c Sex Comparable Sportsa Deaf/Hard-of-Hearing 20 417 4.80 (2.69, 6.90) - Hearing 50 832 6.01 (4.34, 7.68) 1.25 (0.76, 2.08) Note: CI=Confidence interval; IRR=Injury rate ratio Injury rate equals injury counts divided by total athletes IRR equals hearing injury rate divided by deaf/hard-of-hearing injury rate aSex comparable sports are soccer, basketball, baseball, and softball b“Deaf/Hard-of-Hearing” is reference category cIRR is statistically significant (IRR ≠ 1.00)

Counts and rate of concussion among males in all sports combined, as well as in football, soccer, basketball, and baseball individually, are presented in Table 3. For all male sports, there were 14 concussions in athletes who are D/HoH and 77 concussions in athletes who are hearing. Concussion rate in male sports overall was higher in athletes who are hearing than athletes who are D/HoH (IRR=2.84, 95% CI: 1.62, 4.97). Football athletes who are hearing had an increased concussion rate compared to football athletes who are D/HoH (IRR=3.30, 95% CI: 1.71, 6.37). No other male specific injury rate ratios were calculated due to small injury counts.

Table 3. Injury counts by sport for male athletes only Total Injury Rate Injury Counts IRR (95%CI)a Athletes (95%CI) All Sports Deaf/Hard-of-Hearing 14 487 2.87 (1.37, 4.38) - Hearing 77 943 8.17 (6.34, 9.99) 2.84 (1.62, 4.97)b Football Deaf/Hard-of-Hearing 10 276 3.62 (1.38, 5.87) - Hearing 54 452 11.95 (8.76, 15.13) 3.3 (1.71, 6.37)b Soccer Deaf/Hard-of-Hearing 1 58 NA -- Hearing 13 174 7.47 (3.41, 11.53) NA Basketball Deaf/Hard-of-Hearing 2 58 NA -- Hearing 1 81 NA NA Baseball Deaf/Hard-of-Hearing 1 87 NA -- Hearing 9 228 3.95 (1.37, 6.53) NA Note: CI=Confidence interval; IRR=Injury rate ratio Injury rate equals injury counts divided by total athletes IRR equals hearing injury rate divided by deaf/hard-of-hearing injury rate “NA” indicates injury rate or IRR were not calculated due to injury counts < 5 a“Deaf/Hard-of-Hearing” is reference category bIRR is statistically significant (IRR ≠ 1.00)

Counts and rate of concussion among females in all sports combined, as well as in soccer, basketball, and softball individually, are presented in Table 4. For all female sports, there were a total of 16 concussions in athletes who are D/HoH and 27 concussions in athletes who are hearing. Concussion rate in female sports overall did not differ between athletes who are D/HoH and athletes who are hearing. There was no difference in women’s soccer concussion rate between athletes who are D/HoH compared to athletes who are hearing. No other female specific injury rate ratios were calculated due to small injury counts.

Table 4. Injury counts by sport for female athletes only Total Injury Counts Injury Rate (95%CI) IRR (95%CI)a Athletes All Sports Deaf/Hard-of-Hearing 16 206 7.77 (3.96, 11.57) - Hearing 27 341 7.92 (4.93, 10.9) 1.02 (0.56, 1.85) Soccer Deaf/Hard-of-Hearing 10 78 12.82 (4.87, 20.77) - Hearing 10 152 6.58 (2.5, 10.66) 0.51 (0.22, 1.18) Basketball Deaf/Hard-of-Hearing 2 58 NA -- Hearing 11 81 13.58 (5.55, 21.61) NA Softball Deaf/Hard-of-Hearing 4 70 NA -- Hearing 6 108 5.56 (1.11, 10.00) NA Note: CI=Confidence interval; IRR=Injury rate ratio Injury rate equals injury counts divided by total athletes IRR equals hearing injury rate divided by deaf/hard-of-hearing injury rate “NA” indicates injury rate or IRR were not calculated due to injury counts < 5 a“Deaf/Hard-of-Hearing” is reference category

Discussion

The findings of this study highlight some differences in concussion rate between

D/HoH and hearing athletes. When examining all sports combined, all men’s sports, and

football, athletes who are hearing had a higher concussion rate compared to athletes who

are D/HoH. No differences in concussion rate were found between athletes who are

hearing and athletes who are D/HoH for sex comparable sports and all female sports.

Although various concussion epidemiology studies have previously been published, the

results of this study offer the first epidemiological information in a population of athletes

who are D/HoH.

There were differences in concussion rate between athletes who are D/HoH and

athletes who are hearing when comparing all sports, men’s sports, and football. These

differences may exist secondary to possible underreporting of concussions in athletes

who are D/HoH, however, more research is needed to support this. In collegiate athletics,

there are an estimated 11.8% of concussions that are underreported.6 A reason for the

underreporting of concussions may be due to an athletes’ lack of symptom awareness.6 It

is well documented that individuals who are D/HoH are historically poorly educated on

medical and health-related information. Previous literature has demonstrated a deficit of

medical and health knowledge in areas including HIV/AIDs,162 cardiovascular disease,163

cancer prevention,164-167 tobacco use,168 and preventative medicine.169 Overall, these

studies conclude that individuals who are D/HoH may have limited access to health

information and may be ill-equipped to make appropriate health-related decisions. The deficit in medical knowledge may be from a lack of health information available in

ASL,170 limited English reading level,171 and low health literacy,35,172 however, these factors have yet to be studied in athletes who are D/HoH.

Athletes who are D/HoH are at risk for fund-of-information deficit.173 Fund-of- information deficit is a defined as a “distinct limitation in one’s factual knowledge base in comparison to the general population.”172 Due to their hearing loss, access to concussion information through auditory mass media sources such as radio, television, conversations or public announcements is difficult.172,174 Concussion information is often made through these means175 and therefore athletes who are D/HoH may have decreased accessibility to concussion information potentially resulting in underreporting. Clinicians should ensure proper accessibility of medical information, especially sport related concussion, for athletes who are D/HoH.

Individuals who are D/HoH have been found to have vestibular and visual sensory differences compared to individuals who are hearing. Vestibular dysfunction has previously been reported in individuals who are D/HoH compared to individuals who are hearing.13,98,147-151 Additionally, individuals who are D/HoH have demonstrated superior peripheral visual field performance compared to individuals who are hearing including reaction time,153 motion processing,154 orienting and reorienting,152,155 peripheral visual attention,158 and processing of peripheral distractors.152,156,157 However, not all aspects of visional performance for individuals who are D/HoH are improved.158 Individuals who are D/HoH have demonstrated poorer performance compared to individuals who are hearing in central visual field including sustained attention and altering,161 and processing of distractors.156 Additionally, individuals who are D/HoH have also been found to have

44 similar performance in the central visual field compared to individuals who are hearing including visual searching,159 and orienting.155 These sensory differences may act as protective mechanisms for athletes who are D/HoH and therefore, leading to a decrease in concussion rate compared to athletes who are hearing. However, it should be noted that these studies used children13,98,147,150,151 and adults148,149,152-161 who are D/HoH and therefore, the results may not accurately reflect sensory differences for athletes who are

D/HoH.

Regarding communication, the athletes who are D/HoH who participated in this study attend a university where the institution is designed to be barrier-free for students who are D/HoH. Athletes who are deaf prefer to use ASL while athletes who are hard-of- hearing prefer to use oral communication.176 With all medical staff being fluent in both

ASL and English where the study was conducted, there were no communication barriers with reporting injuries. However, this may not be the case at other institutions or high schools where athletes who are D/HoH participate in athletics. Individuals who are deaf, who speak English as a second language or not at all, are at the greatest risk for miscommunication with individuals who are hearing.177 Therefore, it is important for the medical staff to be familiar with the preferred communication mode of athletes who are

D/HoH and accommodate them appropriately (i.e. ASL interpreter) to minimize miscommunication.

Overall, this study provides epidemiological evidence of concussion rate in athletes who are D/HoH. However, there are limitations to note from this study. Factors such as playing time and position played were not collected or included in the analysis

45 and may have an influence on concussion rate of athletes who are D/HoH. Additionally, the generalizability of these findings are only limited to NCAA Division III collegiate athletes, thus future information should be gathered across various collegiate competition levels and also across different high school and youth level sports.

Conclusion

The purpose of this study was to compare concussion rate between athletes who are D/HoH and athletes who are hearing. Athletes in sex comparable sports who are

D/HoH may not have a higher rate of concussion than athletes who are hearing. Rate of concussion in football may be greater among athletes who are hearing compared to athletes who are D/HoH. This finding may be due to historically limited medical and health knowledge among individuals who are D/HoH, potentially resulting in an underreporting of concussions in this population. Additionally, vestibular and visual sensory performance differences may have an influence on concussion rate of athletes who are D/HoH.

Chapter 4: The Effect of Hearing Status on Static and Dynamic Postural Control Performance of Athletes

Abstract

Background: Postural control integrates information from the somatosensory, visual,

and vestibular systems and is often assessed to monitor an athlete’s progress in

rehabilitation after injury. Disturbances to these systems have been proposed as possible

mechanisms for postural control deficiencies. However, postural control of athletes with

possible vestibular dysfunction, such as athletes who are deaf or hard-of-hearing

(D/HoH), has yet to be explored.

Purpose: Determine the effect of hearing status on static and dynamic postural control

performance of athletes.

Methods: Fifty-five collegiate varsity athletes who are D/HoH (20.62±1.80 yrs.,

1.73±0.08 m., 80.34±18.92 kg.) and 100 university club level athletes who are hearing

(20.11±1.59 yrs., 1.76±0.09 m., 77.66±14.37 kg.) from two institutions participated in the

study. Participants completed static and dynamic postural control assessments consisting

of the modified Clinical Test of Sensory Interaction and Balance (mCTSIB) and a jump- landing task, respectively. Center of pressure (CoP) data were collected on a tri-axial force plate for both static and dynamic postural control assessments. For static postural control, total, anterior-posterior (AP), and medial-lateral (ML) CoP excursion, AP and

ML CoP range, 95% ellipse sway area, and AP and ML amplitude root-mean square 47

(RMS) were calculated. For dynamic postural control, time-to-stabilization was

calculated. Independent-sample t-tests were used to test the effect of hearing status on

static and dynamic postural control performance. One-way ANOVAs were used to test differences in static postural control conditions in athletes who are D/HoH and athletes who are hearing seperately. Generalized linear regressions were used to determine effects of hearing status and static postural control condition on static postural control performance. Alpha level was set a priori at p<0.05.

Results: There were statistically significant static postural control differences (p<0.05)

between hearing statuses for conditions 1, 3, and 4 for total, AP, ML CoP excursion, 95%

ellipse sway area, AP and ML range, ML CoP RMS. No statistically significant effect

was found between hearing status for dynamic postural control. Additionally, there was a

statistically significant main effect of condition on all static postural control outcome

measure (p<0.01). Lastly, generalized linear regressions suggested an interaction between

hearing status and condition for ML CoP excursion (p=0.04), AP (p=0.01) and ML

(p=0.02) CoP range, 95% ellipse sway area (p<0.01), and ML CoP RMS (p=0.03).

Conclusion: Athletes who are D/HoH demonstrated increase sway compared to athletes

who are hearing during the mCTSIB. However, there were no differences in dynamic

postural control performance between athletes who are D/HoH and athletes who are

hearing during the time-to-stabilization task. Baseline assessments for static postural

control performance may be warranted for athletes who are D/HoH rather than comparing

to existing normative data.

Introduction

Postural control assessments are fundamental tools used to quantify balance

performance of athletes pre- and post-injury. Static postural control assessments have

been used to characterize differences in double-leg and single-leg balance between athletes who are hearing from various sports5, 17, 23 and to identify deficits following

injury, especially sports-related concussion.19, 21, 43 Dynamic postural control assessments have been used to characterize stabilization strategies of healthy athletes completing a motor task, such as jump-landing,19, 43, 49 and of those following ankle and knee

injuries.45, 55 Postural control assessments can identify balance deficits following a

concussion19, 22, 33 and are therefore well supported by clinicians as tools in the management of concussions.6, 34

Although postural control performance is well documented for healthy and

injured athletes who are hearing,5, 17, 19, 21, 23, 43 limited information is currently available

on characteristics of postural control performance for athletes who are deaf or hard-of-

hearing (D/HoH). This gap in the literature should be addressed to better inform injury

management and return-to-play decisions for athletes who are D/HoH.

Postural control relies on information obtained via somatosensory, visual, and vestibular systems to influence muscular coordination.20, 50 Disturbances to these systems

have been proposed as possible mechanisms for postural control deficiencies.20 Even

prior to head impact disturbance, athletes who are D/HoH may exhibit vestibular

dysfunction due to the proximity of the vestibular apparatus, cochlea, and neurovascular

supply.48 The effects of vestibular dysfunction on postural control are not well

understood and may elicit different postural control characteristics of athletes who are

D/HoH compared to other populations. Previous authors have reported that athletes who are hearing may be at greater risk of injury due to postural control deficiencies,37 little is

known of the effects of vestibular dysfunction in athletes who are D/HoH on postural

control performance.

The World Health Organization (WHO) estimates that there are approximately

466 million people worldwide who are D/HoH.58 In the United States, there are an

estimated 48 million adolescents and adults who have a degree of hearing loss.31

Currently, there are an estimated 692,000 school-aged24 and 30,00047 to 71,00054 post-

secondary students who are D/HoH. Though many school-aged students who are D/HoH participate in mainstream school athletics, there are residential schools for the those who are D/HoH that also have athletic programs.40 Athletes who are D/HoH also participate in

athletics at the collegiate level in the National Collegiate Athletic Association (NCAA).51

In addition to school-aged and collegiate-level athletics, there are also international

competitions for athletes who are D/HoH, such as the Deaflympics.40 This community of athletes is continuing to increase at the high school, collegiate, and international levels but information and research regarding postural control of these athletes is lacking which is crucial in understanding fundamental athletic performance and guiding post-injury management.

Although there is a paucity of literature on athletes who are D/HoH, this literature mostly examines postural control of children who are D/HoH. It is estimated that up to

82% of children who are D/HoH have vestibular dysfunction,2, 9, 39 which may contribute

to greater postural instability and delayed overall motor development compared to their

hearing counterparts.10, 13, 16 Children who are D/HoH who have a cochlear implant

display postural control deficits compared to those without a cochlear implant.12 These

differences, however, may not be evident in a college-aged population who may be more

adapted to a cochlear implant compared to children.

It is important that health care providers understand potential differences in

postural control between athletes who are hearing and athletes who are D/HoH; if

postural control characteristics are different between these athletes, injury management

could be personalized to the athlete to better inform rehabilitation programs. Therefore,

the purpose of this study was to effect of hearing status on static and dynamic postural

control performance of athletes. We hypothesize that there will be an effect of hearing status on static and dynamic postural control performance. Specifically, we hypothesize that athletes who are D/HoH will have larger sway and longer time-to-stability values compared to athletes who are hearing.

Methods

Participants

Fifty-five collegiate varsity athletes who are D/HoH (20.62±1.80 yrs., 1.73±0.08

m., 80.34±18.92 kg.) and 100 university club level athletes who are hearing (20.11±1.59

yrs., 1.76±0.09 m., 77.66±14.37 kg.) from two institutions participated in the study.

Athletes who are D/HoH were recruited from the world’s only university designed to be

barrier-free for students who are D/HoH.

Inclusion and Exclusion Criteria

Inclusion Criteria

• Aged 18-30 years • Gallaudet University varsity athlete o Self-reported deaf or hard-of-hearing status o Currently participating in varsity athletics • The Ohio State University collegiate club athlete o Self-reported hearing status o Currently participating in an organized collegiate club sport

Exclusion Criteria

• Medically diagnosed concussion within 6 months of study participation • Post-concussion syndrome • History of cochlear implantation surgery • Medically diagnosed mental health condition • Current musculoskeletal injury • History of lower extremity surgery • Pregnancy • Known balance disorder or neurological condition that affects balance

Consent and Communication Considerations

Athletes who were D/HoH were given an opportunity to view the consent form in

video form interpreted in American Sign Language (ASL) However, all participants were required to sign the paper consent form whether or not they viewed the ASL interpreted video or not. Additionally, a study member who was fluent in ASL and English was present during the consent process and data collections to answer participants’ questions or provide clarification.

Questionnaire

Prior to completing the postural control assessments, participants completed a

self-reported questionnaire with items regarding their sex, primary sport participation,

concussion history, and hearing status. (Appendix A)

Static and Dynamic Postural Control Assessments

Prior to completing the postural control assessments, all participants had anthropometric measurements taken including height with and without shoes and weight with and without shoes. All participants completed both the static and dynamic postural control assessments during a single testing session. To reduce any potential effects from fatigue caused by the dynamic postural control assessment, the static postural control assessment was completed first followed by the dynamic postural control assessment.

Participants were allowed to practice both assessments prior to testing for safety considerations. Both static and dynamic postural control were assessed on a tri-axial force plate (Bertec FP4060, Bertec Corp., Columbus, OH, USA). All hearing aid devices were removed prior to testing. All postural control assessments were performed in a quiet environment.

Static postural control was assessed using the modified clinical test of sensory interaction and balance (mCTSIB) without shoes. The mCTSIB systematically eliminates or alters sensory feedback. 178 The mCTSIB includes the following four conditions: (1)

standing on firm surface with eyes open (EO), (2) standing on firm surface with eyes

closed (EC), (3) standing on foam surface with EO, and (4) standing on foam surface

with EC (Figure 1). In condition one, all sensory systems that influence postural control

are available. In condition two, vision has been eliminated and the participant will rely on

somatosensory and vestibular input to maintain postural control. In condition three, the

somatosensory system is compromised, and the participant will rely on the visual and

vestibular system to maintain postural control. Lastly, in condition four, vision has been

eliminated and somatosensory has been compromised, therefore the participant must rely

on vestibular input to maintain postural control (Table 5). A medium-density foam pad measuring 19.7” x 16.1” x 2.4” (AirEx Balance Pad Elite, Alcan AirEx AG, Switzerland) was used for conditions 3 and 4. Participants completed three trials of 20 seconds for each condition. Participants were instructed to keep feet together and arms across their chest during all trials. Participants were instructed to keep feet together and arms across their chest during all trials. If participants were not able to complete a 20 second trial, that trial was repeated one additional time. The second trial was not attempted if the subject passed on the first attempt. A condition was considered “passed” if a participant completed either attempt. Participants failed a condition when they took a step to regain their balance, stepped off the force plate, removed their hands from their chest, or opened their eyes during eyes closed conditions. Each participant had at least 20 seconds of rest between each pair of trials.

Table 5. Sensory system(s) compromised and available for sensory input during each condition of the modified Clinical Test of Sensory Interaction and Balance Sensory Sensory Systems(s) Condition Vision Surface System(s) Available for Compromised Input 1 Eyes Open Firm None All Somatosensory 2 Eyes Closed Firm Visual Vestibular Visual 3 Eyes Open Foam Somatosensory Vestibular Visual 4 Eyes Closed Foam Vestibular Somatosensory

Figure 1. Conditions 1 (left) and 3 (right) of the modified Clinical Test of Sensory Interaction and Balance

To assess dynamic postural control, a single-leg jump-landing task with the

participants wearing shoes was used. Prior to assessment, standing reach height was

measured with the participants standing against the wall with their ipsilateral arm to their

dominant leg flexed 180°. Limb dominance was determined by asking the participants

their preferred leg to kick a ball. A height-measuring device (Vertec, Sports Imports,

Columbus, OH, USA) was set at maximum standing reach height prior to maximum vertical jumps. Three maximum double-limb vertical jump trials were performed starting from the ground 70 cm lateral from the Vertec. The participants were instructed to jump off the ground vertically and touch the highest vane possible on the Vertec with the ipsilateral hand to their dominant leg. Maximum vertical height was determined as the difference between the maximum jump height and the standing reach height. The largest maximum vertical height of the three trials was used to calculate a 50-55% jump height threshold for the time to stability (TTS) assessment.

Following the maximum vertical jump test, participants completed the TTS assessment. Prior to testing, participants were given at least three practice trials.

Participants stood on the force plate under the Vertec and performed a jump using bilateral-foot takeoff technique. Participants jumped to 50%-55% of their maximum jump height by touching the Vertec with their dominant leg ipsilateral hand, and then attempt to land on their dominant leg on the force plate. Instructions were given to 1) stabilize as quickly as possible with hands on hips, 2) maintain stance leg in approximately 5° of knee flexion, 3) keep non-stance foot in a neutral position, 4) maintain non-stance leg in approximately 20° of hip flexion and 45° of knee flexion, and 5) remain as stationary as

57 possible in a single-leg stance for 20 seconds (Figure 2). If a participant lost their balance, touched down with their non-stance limb, or did not reach at least 50% maximum jump height, the trial was discarded and repeated. If a participant took more than 10 trials to complete three successful TTS trials, they were excluded from dynamic postural control analyses.

Figure 2. Time-to-stability task

Data Analysis

Center of pressure (CoP) data were calculated from the force plate for all trials.

Ground reaction forces (GRF) and CoP data were processed using a 4th order zero-phase

lag Butterworth filter with a low-pass filter at 10 Hz and 20 Hz, respectively. Custom

MATLAB (MathWorks, Inc., Natick, MA, US) code was used to calculate all outcome variables.

Static postural control performance was quantified via total, AP, and ML CoP excursion, 95% ellipse sway area, and AP and ML CoP range. Each of the aforementioned outcome variables were calculated for each trial performed. For each static trial, the first and last five seconds were excluded from the analyses to account for postural variability during task initiation and possible fatigue. Overall condition means were calculated from the means of the three trials of a single condition, which were used in the analyses for each participant.

Dynamic postural control performance was quantified via a TTS task.

Stabilization time was calculated as the time when the vertical GRF reached and stayed within 5% of the participants’ body weight for at least 500 ms following landing. 179-182

TTS was calculated for each successful jump trial, then means from the three successful

trials were averaged for an overall mean of each participant and used for the analysis.

Also recorded were the number of attempts to complete three successful TTS trials, maximum double-leg vertical height jump, 50% of maximum double-leg vertical height jump, and 55% of maximum double-leg vertical height jump. Maximum vertical jump

60 height was calculated as the difference between the highest vane of the Vertec reached and the standing reach height. The force plate height was accounted for during the 50-

55% vertical jump height threshold calculation secondary to the TTS trials being performed on the force plate while the maximum vertical jump test was performed off of the force plate.

Statistical Analysis

Descriptive statistics were used to describe the distributions of participant demographics. Additionally, Chi-square tests were performed to assess the associations between participant demographics and hearing status (Table 6). Independent-sample t- tests were used to compare static and dynamic postural control performance between hearing status, sex, age, and concussion history. Effect sizes for static postural control performance by hearing status were calculated for each condition through the Cohen’s d.

Effect sizes were interpreted as small: 0.20, medium: 0.5, and large: 0.8. One-way

ANOVAs were used to test the differences in static postural control performance among four experimental conditions; EO with firm surface, EC with firm surface, EO with foam surface, and EC with foam surface in athletes who are D/HoH and athletes who are hearing separately. Bonferroni corrected pairwise comparisons were evaluated post hoc for significant pairwise differences. Generalized linear regressions were used to determine the effects of hearing status and experimental conditions and their interactions on static postural control performance.

Table 6. Characteristics of participants Deaf or Hard- Hearing of-Hearing p-value n (%) n (%) Sex Male 68 (68.00) 36 (65.45) 0.75 Female 32 (32.00) 19 (34.55) Age 18-21 66 (66.00) 28 (50.91) 0.07 22-28 34 (34.00) 27 (49.09) Year in School First Year 16 (16.00) 18 (32.73) Second Year 32 (32.00) 10 (18.18) Third Year 26 (26.00) 18 (32.73) 0.13 Fourth Year 20 (20.00) 8 (14.55) Fifth Year or Greater 6 (6.00) 1 (1.82) Sport Soccer 29 (29.00) 10 (18.18) Basketball 8 (8.00) 11 (20.00) Volleyball 12 (12.0) 1 (1.82) Softball 4 (4.00) 6 (10.91) Baseball 8 (8.00) 13 (23.64) <0.01 Football 0 (0.00) 11 (20.00) Track and Field 0 (0.00) 2 (3.64) Swimming 0 (0.00) 1 (1.82) Rugby 17 (17.00) 0 (0.00) Hockey 22 (22.00) 0 (0.00) Concussion History Yes 42 (42.00) 11 (20.00) <0.01 No 58 (58.00) 44 (80.00) Note: p-value from chi-square test of independence For static postural control, three participants did not successfully complete condition 4 and therefore, were not included in any analysis using condition 4 as an outcome. For dynamic postural control, four participants did not successfully complete the protocol and were excluded from further analysis.

Results

Static Postural Control Performance and Hearing Status

Total Center-of-Pressure Excursion

Athletes who are D/HoH had statistically significant larger total CoP excursion for condition 1 (p<0.01), condition 3 (p<0.01), and condition 4 (p=0.01) than athletes who are hearing (Figure 3). No statistically significant differences in total CoP excursion for condition 2 between athletes who are D/HoH and hearing (p=0.45). Additionally, no statistically significant differences were found between sex, age, and concussion history for total CoP excursion for each of the four conditions (Table 7).

Figure 3. Total center-of-pressure excursion of athletes who are deaf or hard-of- hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface*

0 20 40 60 80 100 120 Total Center-of-Pressure Excursion (Centimeters)

Deaf or Hard-of-Hearing Hearing Note: Statistical significance is denoted by * mCTSIB = modified Clinical Test of Sensory Interaction and Balance EO = eyes open; EC = eyes closed Error bars represent standard deviation

Table 7. Total center -of-pressure excursion by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 14.14 (3.14) 22.25 (7.74) 22.77 (4.66) 61.33 (19.17) Deaf or Hard- <0.01 0.49 0.45 0.12 <0.01 1.02 0.01 0.40 55 16.11 (4.78) 23.35 (9.98) 30.92 (10.33) 72.48 (34.57) of-Hearing Sex Male 104 14.83 (3.84) 23.01 (8.51) 25.80 (8.03) 67.44 (27.68) 0.97 <0.01 0.44 0.13 0.77 0.05 0.11 0.29 Female 51 14.86 (4.07) 21.88 (8.78) 25.39 (8.51) 60.31 (21.28) Age 18-20 93 14.65 (3.69) 22.32 (8.42) 25.56 (8.26) 62.94 (24.05) 0.46 0.12 0.58 .09 0.84 0.03 0.20 0.21 21-28 62 15.12 (4.23) 23.11 (8.87) 25.82 (8.10) 68.44 (28.40) Concussion

History Yes 53 14.43 (3.98) 21.85 (6.08) 24.39 (6.31) 60.10 (20.24) 0.35 0.16 0.41 0.15 0.16 0.25 0.08 0.31 No 102 15.05 (3.87) 23.05 (9.64) 26.33 (8.94) 67.84 (28.25) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Anterior-Posterior Center-of-Pressure Excursion

Athletes who are D/HoH had statistically significant larger anterior-posterior CoP

excursion for condition 1 (p=0.02), condition 3 (p<0.01), and condition 4 (p=0.01) than

athletes who are hearing (Figure 4). No statistically significant differences were found in

anterior-posterior CoP excursion for condition 2 between athletes who are D/HoH and

hearing (p=0.58). Additionally, no statistically significant differences between sex, age,

and concussion history were found for anterior-posterior CoP excursion for each of the four conditions (Table 8).

Figure 4. Anterior-posterior center-of-pressure excursion athletes who are deaf or hard-of-hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB EO and firm surface*

0 10 20 30 40 50 60 70 80 Anterior-Posterior Center-of-Pressure Excursion (Centimeters)

Deaf or Hard-of-Hearing Hearing

Note: Statistical significance is denoted by * mCTSIB = modified Clinical Test of Sensory Interaction and Balance EO = eyes open; EC = eyes closed Error bars represent standard deviation

Table 8. Anterior-posterior center-of-pressure excursion by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 8.62 (2.06) 13.66 (5.19) 13.38 (3.01) 38.60 (13.87) Deaf or Hard- 0.02 0.36 0.58 0.09 <0.01 0.88 0.01 0.39 55 9.61 (3.25) 14.18 (6.07) 17.82 (6.44) 45.99 (22.86) of-Hearing Sex Male 104 8.99 (2.36) 14.21 (5.40) 15.01 (4.89) 43.01 (19.52) 0.92 0.02 0.24 0.20 0.84 0.03 0.06 036 Female 51 8.94 (3.00) 13.10 (5.69) 14.84 (5.24) 37.17 (12.55) Age 18-20 93 8.78 (2.11) 13.71 (5.21) 15.00 (5.14) 39.41 (15.49) 0.26 0.18 0.71 .0.06 0.89 0.02 0.15 0.24 21-28 62 9.26 (3.15) 14.05 (5.95) 14.89 (4.79) 43.69 (20.54) Concussion

History Yes 53 8.94 (3.06) 13.40 (4.30) 14.39 (4.09) 37.60 (14.27) 0.07 0.90 0.02 0.46 0.13 0.31 0.18 0.32 No 102 8.99 (2.31) 14.08 (6.04) 15.25 (5.39) 43.02 (19.16) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Medial-Lateral Center-of-Pressure Excursion

Athletes who are D/HoH had statistically significant larger medial-lateral CoP

excursion for condition 1 (p<0.01), condition 3 (p<0.01), and condition 4 (p=0.01)

(Figure 5). No statistically significant differences in ML CoP excursion for condition 2

between athletes who are D/HoH and hearing (p=0.39). Additionally, no statistically

significant differences between sex, age, and concussion history for medial-lateral CoP excursion for each of the four conditions (Table 9).

Figure 5. Medial-lateral center-of-pressure excursion of athletes who are deaf or hard-of-hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface*

0 10 20 30 40 50 60 70 80 Medial-Lateral Center-of-Pressure Excursion (Centimeters)

Deaf or Hard-of-Hearing Hearing

Note: Statistical significance is denoted by * mCTSIB = modified Clinical Test of Sensory Interaction and Balance EO = eyes open; EC = eyes closed Error bars represent standard deviation

Table 9. Medial-lateral center-of-pressure excursion by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 9.35 (2.31) 14.61 (5.13) 15.57 (3.42) 39.39 (11.40) Deaf or Hard- <0.01 0.54 0.39 0.14 <0.01 1.05 0.01 0.38 55 10.83 (3.08) 15.45 (7.08) 21.47 (7.14) 46.07 (21.75) of-Hearing Sex Male 104 9.85 (2.83) 15.03 (5.89) 17.78 (5.69) 42.78 (16.40) 0.87 0.03 0.71 0.06 0.73 0.06 0.22 0.22 Female 51 9.93 (2.42) 14.65 (5.93) 17.43 (6.01) 39.36 (14.92) Age 18-20 93 9.83 (2.83) 14.63 (5.93) 17.47 (5.78) 40.47 (15.72) 0.77 0.04 0.48 0.12 0.61 0.08 0.26 0.19 21-28 62 9.95 (2.51) 15.31 (5.84) 17.95 (5.82) 43.47 (16.30) Concussion

History Yes 53 9.42 (2.30) 14.35 (4.09) 16.64 (4.42) 38.84 (12.45) 0.13 0.07 0.40 0.15 0.11 0.28 0.11 0.29 No 102 10.11 (2.87) 15.19 (6.63) 18.19 (6.33) 43.19 (17.44) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Anterior-Posterior Center-of-Pressure Range

Athletes who are D/HoH had statistically significant larger anterior-posterior CoP range for condition 1 (p<0.01), condition 3 (p<0.01), and condition 4 (p=0.04) (Figure 6).

No statistically significant different in AP CoP range for condition 2 between athletes who are D/HoH and hearing (p=0.90). Additionally, there was a statistically significant difference between those with and without a history of concussion for condition 4

(p=0.02). No other statistically significant differences between sex, age, and concussion history for anterior-posterior CoP range for each of the four conditions (Table 10).

Figure 6. Anterior-posterior center-of-pressure range of athletes who are deaf or hard-of-hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface*

0 1 2 3 4 5 6 7 8 9 Anterior-Posterior Center-of-Pressure Range (Centimeters)

Table 10. Anterior-posterior center-of-pressure range by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 1.52 (0.43) 2.30 (1.12) 2.50 (0.55) 5.49 (1.26) Deaf or Hard- <0.01 0.55 0.90 0.02 <0.01 0.89 0.04 0.33 55 1.82 (0.64) 2.28 (0.94) 3.25 (1.05) 6.08 (2.19) of-Hearing Sex Male 104 1.61 (0.48) 2.33 (1.08) 2.75 (0.82) 5.81 (1.74) 0.76 0.05 0.61 0.10 0.83 0.05 0.21 0.23 Female 51 1.64 (0.62) 2.23 (1.00) 2.79 (0.90) 5.45 (1.43) Age 18-20 93 1.60 (0.45) 2.27 (0.86) 2.72 (0.79) 5.62 (1.55) 0.56 0.09 0.75 0.05 0.41 0.13 0.47 0.11 21-28 62 1.65 (0.63) 2.33 (1.30) 2.83 (0.93) 5.81 (1.81) Concussion

History Yes 53 1.60 (0.63) 2.27 (1.31) 2.66 (0.80) 5.26 (1.38) 0.69 0.07 0.84 0.04 0.27 0.19 0.02 0.43 No 102 1.64 (0.47) 2.31 (0.90) 2.82 (0.87) 5.93 (1.75) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Medial-Lateral Center-of-Pressure Range

Athletes who are D/HoH had statistically significant larger medial-lateral CoP range for condition 1 (p<0.01), condition 3 (p<0.01), and condition 4 (p<0.01) (Figure 7).

No statistically significant differences in ML CoP range for condition 2 between athletes who are D/HoH and hearing (p=0.19). Additionally, there was a statistically significant difference between those with and without a history of concussion for condition 1

(p=0.03). No other statistically significant differences between sex, age, and concussion history for medial lateral CoP range for each of the four conditions (Table 11).

Figure 7. Medial-lateral center-of-pressure range of athletes who are deaf or hard- of-hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface*

0 1 2 3 4 5 6 7 8 9 10 Medial-Lateral Center-of-Pressure Range (Centimeters)

Table 11. Medial-lateral center-of-pressure range by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 1.64 (0.37) 2.47 (0.82) 2.46 (0.50) 5.36 (1.25) Deaf or Hard- <0.01 0.79 0.19 0.21 <0.01 1.08 <0.01 0.49 55 2.06 (0.65) 2.69 (1.26) 3.43 (1.17) 6.31 (2.46) of-Hearing Sex Male 104 1.77 (0.54) 2.55 (1.00) 2.79 (0.91) 5.82 (1.82) 0.43 0.12 0.96 0.01 0.77 0.05 0.18 0.23 Female 51 1.83 (0.49) 2.54 (1.03) 2.84 (0.96) 5.40 (1.76) Age 18-20 93 1.81 (0.54) 2.52 (0.92) 2.75 (0.88) 5.54 (1.73) 0.63 0.10 0.67 0.07 0.33 0.16 0.22 0.20 21-28 62 1.76 (0.50) 2.59 (1.13) 2.90 (0.99) 5.90 (1.91) Concussion

History Yes 53 1.66 (0.40) 2.42 (0.91) 2.64 (0.81) 5.30 (1.43) 0.03 0.41 0.25 0.19 0.11 0.28 0.06 0.34 No 102 1.86 (0.57) 2.61 (1.05) 2.89 (0.97) 5.89 (1.96) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

95% Ellipse Sway Area

Athletes who are D/HoH had statistically significant larger 95% ellipse sway area for condition 1 (p<0.01), condition 3 (p<0.01), and condition 4 (p<0.01) than athletes who are hearing (Figure 8). No statistically significant differences in 95% ellipse sway area for condition 2 between athletes who are D/HoH and hearing (p=0.15). No statistically significant differences were observed between sex, age, and concussion history for 95% ellipse sway area for each of the four conditions (Table 12).

Figure 8. 95% ellipse sway area of athletes who are deaf or hard-of-hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface*

0 10 20 30 40 50 60 70 80 95% Ellipse Sway Area (Centimeters2)

Deaf or Hard-of-Hearing Hearing

Note: Statistical significance is denoted by * mCTSIB = modified Clinical Test of Sensory Interaction and Balance EO = eyes open; EC = eyes closed Error bars represent standard deviation

Table 12. 95% ellipse sway area by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 2.44 (1.17) 5.22 (3.51) 5.69 (2.24) 26.95 (11.76) 0.52 Deaf or Hard- <0.01 0.62 0.15 0.22 <0.01 0.88 <0.01 55 3.67 (2.57) 6.46 (7.25) 11.13 (7.99) 40.70 (35.28) of-Hearing Sex Male 104 2.81 (1.60) 5.64 (5.30) 7.46 (5.08) 32.89 (24.60) 0.17 0.54 0.01 0.94 0.01 0.62 0.08 0.35 Female 51 3.01 (2.38) 5.70 (4.94) 7.95 (6.87) 29.04 (21.12) Age 18-20 93 2.87 (1.57) 5.51 (3.81) 7.32 (4.87) 30.21 (22.70) 0.15 0.96 0.01 0.65 0.07 0.43 0.13 0.36 21-28 62 2.88 (2.29) 5.89 (6.73) 8.07 (6.80) 33.81 (24.76) Concussion

History Yes 53 2.61 (2.24) 4.94 (4.00) 6.80 (6.15) 26.82 (16.64) 0.34 0.21 0.20 0.21 0.22 0.19 0.21 0.06 No 102 3.01 (1.67) 6.03 (5.66) 8.05 (5.46) 34.24 (26.21) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters2 Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Anterior-Posterior Center-of-Pressure Root Mean Square

There were no statistically significant differences between athletes who are

D/HoH and athletes who are hearing for AP CoP RMS for any of the conditions (Figure

9). Athletes who are female had a statistically significant larger anterior-posterior CoP

RMS compared to men for condition 1 (p=0.01). There were no statistically significant differences between hearing status, age, and concussion history for anterior-posterior CoP

RMS for each of the four conditions (Table 13).

Figure 9. Anterior-posterior center-of-pressure root mean square of athletes who are deaf or hard-of-hearing and hearing

EC and foam surface

EO and foam surface

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface

0 1 2 3 4 5 6 7 8 Anterior-Posterior Center-of-Pressure Root Mean Square (Centimeters)

Deaf or Hard-of-Hearing Hearing

Note: Statistical significance is denoted by * mCTSIB = modified Clinical Test of Sensory Interaction and Balance EO = eyes open; EC = eyes closed Error bars represent standard deviation

Table 13. Anterior-posterior center-of-pressure root mean square by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 4.14 (2.41) 4.08 (2.09) 3.15 (1.70) 3.10 (1.36) Deaf or Hard- 0.77 0.05 0.58 0.56 0.44 0.13 0.72 0.06 55 4.03 (2.31) 4.30 (2.68) 2.92 (1.82) 3.20 (2.08) of-Hearing Sex Male 104 3.76 (2.20) 3.97 (2.25) 2.97 (1.61) 3.22 (1.77) 0.01 0.43 0.15 0.25 0.56 0.12 0.33 0.17 Female 51 4.80 (2.57) 4.55 (2.41) 3.18 (1.91) 2.95 (1.32) Age 18-20 93 4.24 (2.44) 4.29 (2.39) 3.01 (1.62) 3.12 (1.57) 0.38 0.14 0.38 0.14 0.63 0.08 0.88 0.02 21-28 62 3.90 (2.27) 3.96 (2.20) 3.15 (1.92) 3.16 (1.74) Concussion

History Yes 53 4.10 (2.70) 3.94 (2.36) 2.91 (1.66) 3.10 (1.57) 1.00 0.00 0.38 0.15 0.41 0.14 0.85 0.03 No 102 4.10 (2.19) 4.28 (2.29) 3.15 (1.79) 3.15 (1.68) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Medial-Lateral Center-of-Pressure Root Mean Square

Athletes who are D/HoH had statistically significant larger ML CoP RMS for condition 1 (p<0.01), condition 3 (p<0.01), and condition 4 (p=0.04) (Figure 10). No statistically significant differences in ML CoP RMS for condition 2 between athletes who are D/HoH and hearing (p=0.09). Additionally, there was a statistically significant difference between those with and without a history of concussion for condition 1

(p=0.04) and condition 4 (p=0.02). No other statistically significant differences between sex, age, and concussion history for ML CoP range for each of the four conditions (Table

14).

Figure 10. Medial-lateral center-of-pressure root mean square of athletes who are deaf or hard-of-hearing and hearing

EC and foam surface*

EO and foam surface*

EC and firm surface mCTSIB Condition mCTSIB

EO and firm surface*

0 0.5 1 1.5 2 2.5 Medial-Lateral Center-of-Pressure Root Mean Sqaure (Centimeters)

Deaf or Hard-of-Hearing Hearing

Note: Statistical significance is denoted by * mCTSIB = modified Clinical Test of Sensory Interaction and Balance EO = eyes open; EC = eyes closed Error bars represent standard deviation

Table 14. Medial-lateral center-of-pressure root mean square by demographic Condition 1 Condition 2 Condition 3 Condition 4

(EO, Firm) (EC, Firm) (EO, Foam) (EC, Firm) n Mean (SD) p d Mean (SD) p d Mean (SD) p d Mean (SD) p d Hearing Status Hearing 100 0.38 (0.09) 0.54 (0.17) 0.54 (0.11) 1.19 (0.27) Deaf or Hard- <0.01 0.73 0.09 0.26 <0.01 1.14 <0.01 0.48 55 0.47 (0.15) 0.60 (0.28) 0.76 (0.25) 1.41 (0.59) of-Hearing Sex Male 104 0.40 (0.12) 0.56 (0.22) 0.62 (0.20) 1.29 (0.42) 0.35 0.16 0.98 0.05 0.99 0.00 0.24 0.19 Female 51 0.42 (0.13) 0.57 (0.22) 0.62 (0.21) 1.21 (0.42) Age 18-20 93 0.41 (0.12) 0.56 (0.21) 0.61 (0.19) 1.24 (0.40) 0.54 0.08 0.90 0.01 0.41 0.15 0.31 0.17 21-28 62 0.40 (.13) 0.57 (0.24) 0.64 (0.21) 1.31 (0.44) Concussion

History Yes 53 0.38 (0.11) 0.53 (0.17) 0.58 (0.18) 1.17 (0.33) 0.04 0.33 0.11 0.24 0.09 0.31 0.05 0.39 No 102 0.42 (0.13) 0.58 (0.24) 0.64 (0.21) 1.32 (0.45) Note: p-value from t-tests; EO = eyes open; EC = eyes closed; SD = standard deviation; p = p-value; d = Cohen’s d Means and standard deviations are in centimeters Three participants who are deaf or hard-of-hearing did not successfully complete condition 4 Two females and one male did not successfully complete condition 4 One individual who is 18-20 years old and 2 who are 21-28 years old did not successfully complete condition 4 Three with no history of concussion did not complete condition 4

Dynamic Postural Control Performance and Hearing Status

Time-to-Stability

There were no statistically significant differences in the time-to-stability between athletes who are D/HoH and who are hearing (p=0.26) (Figure 11). Additionally, there were no differences in time-to-stability between sex (p=0.33), age (p=0.17), and concussion history (p=0.97).

Figure 11. Time-to-stability of athletes who are deaf or hard-of-hearing and hearing

Time-to-Stability

0 0.5 1 1.5 2 2.5 3 Seconds

Deaf or Hard-of-Hearing Hearing

Note: Error bars represent standard deviation

Static Postural Control Performance and Condition

A one-way within subjects ANOVA was conducted to compare the effect of condition on static postural control performance for athletes who are D/HoH and athletes who are hearing (Table 15).

Table 15. Static postural control performance by condition Condition 1 Condition 2 Condition 3 Condition 4 (EO, Firm) (EC, Firm) (EO, Foam) (EC, Foam) Mean (SD) Mean (SD) Mean (SD) Mean(SD) Athletes who are D/HoH Total CoP Excursion (cm) 15.98 (4.73)†& 22.64 (9.42)* 30.12 (9.65)†^ 72.48 (34.57)*^& AP CoP Excursion (cm) 9.61 (3.29)†& 14.07 (6.05)* 17.47 (6.10)†^ 45.99 (22.86)*^& ML CoP Excursion (cm) 10.68 (2.96)^& 14.70 (6.22)*§ 20.80 (6.56)†^§ 46.07 (21.75)*†& AP CoP Range (cm) 1.83 (0.65)^& 2.26 (0.93)*§ 3.22 (1.06)†^§ 6.08 (2.19)*†& ML CoP Range (cm) 2.05 (0.64)^& 2.60 (1.18)*§ 3.36 (1.15)†^§ 6.31 (2.46)*†& 95% Ellipse Sway Area (cm2) 3.68 (2.62)*& 6.22 (7.25)*† 10.81 (7.99)†^& 40.70 (35.28)^ AP CoP RMS (cm) 3.20 (2.08)* 4.32 (2.74)†^ 2.86 (1.75)*^ 3.20 (2.08)† ML CoP RMS (cm) 0.46 (0.15)^& 0.59 (0.27)*§ 0.74 (0.24)†^§ 1.41 (0.59)*†& Athletes who are hearing Total CoP Excursion (cm) 14.12 (3.13)*†^ 22.24 (7.70)*& 22.72 (4.66)†§ 61.16 (19.15)^&§ AP CoP Excursion (cm) 8.61 (2.05)*†^ 13.66 (5.16)*& 13.38 (2.99)†§ 38.51 (13.83)^&§ ML CoP Excursion (cm) 9.34 (2.30)*†^ 14.59 (5.10)*& 15.52 (3.45)†§ 39.27 (11.41)^&§ AP CoP Range (cm) 1.51 (0.43)*†^ 2.30 (1.11)*& 0.56 (2.49)†§ 5.49 (1.25)^&§ ML CoP Range (cm) 1.64 (0.37)*†^ 2.47 (0.82)*& 2.45 (0.50)†§ 5.35 (1.25)^&§ 95% Ellipse Sway Area (cm2) 2.43 (1.16)*†^ 5.21 (3.49)*& 5.65 (2.26)†§ 26.85 (11.75)^&§ AP CoP RMS (cm) 4.15 (2.40)^& 4.07 (2.08)*§ 3.13 (1.70)†^§ 3.09 (1.35)*†& ML CoP RMS (cm) 0.38 (0.09)*†^ 0.54 (0.17)*& 0.54 (0.11)†§ 1.19 (0.27)^&§ Note: Significant differences between conditions are denoted *, †, ^, & and § EO = eyes open; EC = eyes closed; CoP = center-of-pressure; AP = anterior-posterior; ML = medial-lateral; RMS = root mean square

Total Center-of-Pressure Excursion

For athletes who are D/HoH, there was a significant main effect of condition on total CoP excursion at the p<0.05 level for the four conditions [F(3, 153)=121.70, p<0.01]. Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except for conditions

1 and 2 as well as 2 and 3.

For athletes who are hearing, there was a significant main effect of condition on total CoP excursion at the p<0.05 level for the four conditions [F(3, 300)=517.50, p<0.01]. Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except for conditions

2 and 3.

Anterior-Posterior Center-of-Pressure Excursion

For athletes who are D/HoH, there was a significant main effect of condition on

AP CoP excursion at the p<0.05 level for the four conditions [F(3, 153)=113.90, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2 as well as 2 and 3.

For athletes who are hearing, there was a significant main effect of condition on

AP CoP excursion at the p<0.05 level for the four conditions [F(3, 300)=405.60, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3.

Medial-Lateral Center-of-Pressure Excursion

For athletes who are D/HoH, there was a significant main effect of condition on

ML CoP excursion at the p<0.05 level for the four conditions [F(3, 153)=120.00, p<0.01]. Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2.

For athletes who are hearing, there was a significant main effect of condition on

ML CoP excursion at the p<0.05 level for the four conditions [F(3, 300)=551.40, p<0.01]. Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3.

Anterior-Posterior Center-of-Pressure Range

For athletes who are D/HoH, there was a significant main effect of condition on

AP CoP range at the p<0.05 level for the four conditions [F(3, 153)=149.40, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2.

For athletes who are hearing, there was a significant main effect of condition on

AP CoP range at the p<0.05 level for the four conditions [F(3, 300)=505.20, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3.

Medial-Lateral Center-of-Pressure Range

For athletes who are D/HoH, there was a significant main effect of condition on

ML CoP range at the p<0.05 level for the four conditions [F(3, 153)=130.30, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2.

For athletes who are hearing, there was a significant main effect of condition on

ML CoP range at the p<0.05 level for the four conditions [F(3, 300)=606.70, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3.

95% Ellipse Sway Area

For athletes who are D/HoH, there was a significant main effect of condition on

95% ellipse sway area at the p<0.05 level for the four conditions [F(3, 153)=54.13, p<0.01]. Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3 as well as conditions 1 and 3.

For athletes who are hearing, there was a significant main effect of condition on

95% ellipse sway area at the p<0.05 level for the four conditions [F(3, 300)=422.1, p<0.01]. Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3.

Anterior-Posterior Center-of-Pressure Root Mean Square

For athletes who are D/HoH, there was a significant main effect of condition on

AP CoP RMS at the p<0.05 level for the four conditions [F(3, 153)=9.45, p<0.01]. Post- hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2, conditions 1 and 4, and conditions 3 and 4.

For athletes who are hearing, there was a significant main effect of condition on

AP CoP RMS at the p<0.05 level for the four conditions [F(3, 300)=16.87, p<0.01]. Post- hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2.

Medial-Lateral Center-of-Pressure Root Mean Square

For athletes who are D/HoH, there was a significant main effect of condition on

ML CoP RMS at the p<0.05 level for the four conditions [F(3, 153)=116.70, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 1 and 2.

For athletes who are hearing, there was a significant main effect of condition on

ML CoP RMS at the p<0.05 level for the four conditions [F(3, 300)=669.30, p<0.01].

Post-hoc pairwise comparisons using the Bonferroni indicated that there were statistically significant pairwise differences between all conditions except conditions 2 and 3.

Static Postural Control Performance Regression Model

Generalized linear regressions were used to model the outcome of static postural control performance based on hearing status, mCTSIB condition, and the interaction of hearing status and mCTSIB condition (Table 16).

Table 16. Generalized linear regression results Hearing Condition Hearing x Condition

Sum of Sum of p-value Sum of Square p-value p-value Squares Squares Total CoP Excursion 3011.94 <0.01 209982.09 <0.01 1368.37 0.06 AP CoP Excursion 1037.96 <0.01 87652.46 <0.01 548.80 0.09 ML CoP Excursion 1362.00 <0.01 82277.31 <0.01 592.08 0.04 AP CoP Range 14.81 0.01 1292.47 <0.01 11.03 0.01 ML CoP Range 42.89 <0.01 2280.46 <0.01 10.67 0.02 95% Ellipse Sway area 3351.87 <0.01 79316.81 <0.01 2521.64 <0.01 AP CoP RMS 0.36 0.85 169.61 <0.01 3.77 0.64 ML CoP RMS 2.31 <0.01 58.09 <0.01 0.49 0.03 Note: EO = eyes open; EC = eyes closed; CoP = center-of-pressure; AP = anterior-posterior; ML = medial-lateral; RMS = root mean square

Total Center-of-Pressure Excursion

The results from the regression indicated that a significant regression equation for

total CoP excursion was found [F(160, 459)=9.55, p<0.01], with an R2 of 0.77. Hearing

status (p<0.01) and condition (p<0.01) significantly influenced total CoP excursion.

However, the interaction between hearing status and condition was not statistically

significant (p=0.06).

Anterior-Posterior Center-of-Pressure Excursion

The results of the regression indicated that a significant regression equation for

AP CoP excursion was found [F(160, 459)=8.86, p<0.01], with an R2 of 0.76. Hearing

status (p<0.01) and condition (p<0.01) significantly influenced AP CoP excursion.

However, the interaction between hearing status and condition was not statistically

significant (p=0.09).

Medial-Lateral Center-of-Pressure Excursion

The results of the regression analysis indicated that relationships of hearing status,

condition and ML CoP excursion were statistically significant [F(160, 459)=9.42,

p<0.01], with an R2 of 0.77. Hearing status (p<0.01), condition (p<0.01), significantly

influenced ML CoP excursion. There was significant interaction between hearing status

and condition (p=0.04). Further stratified analysis showed that in conditions 1 (p<0.01), 3

(p<0.01), and 4 (p=0.01) there was statistically significant difference in ML CoP

excursion between athletes who are D/HoH and hearing, but in condition 2 there was no

statistically significant difference in ML CoP excursion between athletes who are D/HoH

and athletes who are hearing (p=0.92).

Anterior-Posterior Center-of-Pressure Range

The results of the regression indicated that a significant regression equation for

AP CoP range was found [F(160, 459)=11.02, p<0.01], with an R2 of 0.79. Hearing status

(p=0.01), condition (p<0.01), and the interaction between hearing status and condition

(p=0.01) significantly influenced AP CoP range. Further stratified analysis showed that in

conditions 1 (p<0.01), 3 (p<0.01), and 4 (p=0.01) there was statistically significant difference in AP CoP range between athletes who are D/HoH and hearing, and in condition 2 there was no statistically significant difference in AP CoP range between athletes who are D/HoH and hearing (p=0.82).

Medial-Lateral Center-of-Pressure Range

The results of the regression indicated that a significant regression equation for

ML CoP range was found [F(160, 459)=10.42, p<0.01], with an R2 of 0.78. Hearing status (p<0.01), condition (p<0.01), and the interaction between hearing status and condition (p=0.02) significantly influenced ML CoP range. Further stratified analysis showed that in conditions 1 (p<0.01), 3 (p<0.01), and 4 (p=0.01) there was statistically significant differences in ML CoP range between athletes who are D/HoH and hearing, and in condition 2 there is no statistically significant difference in ML CoP range between athletes who are D/HoH and hearing (p=0.42).

95% Ellipse Sway Area

The results of the regression indicated that a significant regression equation for

95% ellipse sway area was found [F(160, 459)=10.42, p<0.01], with an R2 of 0.68.

Hearing status (p<0.01), condition (p<0.01), and the interaction between hearing status

and condition (p<0.02) significantly influenced 95% ellipse. Further stratified analysis

showed that in conditions 1 (p<0.01), 3 (p<0.01), and 4 (p=0.01) there is statistically

significant difference in 95% ellipse between athletes who are D/HoH and hearing, and in

condition 2 there is no statistically significant difference in 95% ellipse sway area

between athletes who are D/HoH and hearing (p=0.25).

Anterior-Posterior Center-of-Pressure Root-Mean-Square

The results of the regression indicated that a significant regression equation for

AP CoP RMS was found [F(160, 459)=4.82, p<0.01], with an R2 of 0.63. Condition

(p<0.01) significantly influenced AP CoP RMS. However, hearing status (p=0.85) and

the interaction between hearing status and condition were not statistically significant

(p=0.64).

Medial-Lateral Center-of-Pressure Root-Mean-Square

The results of the regression indicated that a significant regression equation for

ML CoP RMS was found [F(160, 459)=10.29, p<0.01], with an R2 of 0.78. Hearing status

(p<0.01), condition (p<0.01), and the interaction between hearing status and condition

(p<0.01) significantly influenced ML CoP RMS. Further stratified analysis showed that

in conditions 1 (p<0.01), 3 (p<0.01), and 4 (p=0.01) there was statistically significant

differences in ML RMS between athletes who are D/HoH and hearing, and in condition 2

there is no statistically significant difference in ML RMS between athletes who are

D/HoH and hearing (p=0.22).

Discussion

Static and dynamic postural control performance of collegiate athletes who are

D/HoH is lacking in the literature. Understanding postural control performance in this

population is crucial to assist in guiding rehabilitation programs, concussion

management, and return-to-play decisions following injury. This study reported postural

control performance of athletes who are D/HoH and hearing during the mCTSIB and

vertical jump time to stability tasks. Differences in static postural control performance

were observed between athletes who are D/HoH and athletes who are hearing; however,

no differences between groups were observed for dynamic postural control performance.

The static postural control assessment used in this study, the mCTSIB,

systematically assesses the contributions of different sensory systems on static postural control.178 The results suggest that there were consistent statistically significant group

differences between athletes who are D/HoH and athletes who are hearing for conditions

1, 3, and 4 for the static postural control outcomes total, AP, and ML CoP excursion, AP

and ML range, 95% ellipse, and ML CoP RMS. Specifically, athletes who are D/HoH

had increase sway values when compared to athletes who are hearing whereas condition

2 did not yield statistical differences between groups. These differences may be due to

vestibular co-morbidity or altered sensory processing in some of the individuals who are

D/HoH compared to individuals who are hearing.99,183

Condition 1 of the mCTSIB consists of standing on a firm surface with eyes

open.178 Despite all sensory systems being available for input, athletes who are D/HoH

had increased sway for all static postural control outcome measures except AP CoP RMS, 100

compared to athletes who are hearing. This finding is inconsistent with previous findings

by Güzel et al.114 who examined static postural control performance of elite soccer

players who are D/HoH (n=18) compared to individuals who are hearing and sedentary

(n=10). It should be noted that Güzel et al.114 used a Biodex-Balance System to assess static postural control with overall stability index (OSI), medial-lateral index (MLI), and anterior-posterior index (API) as outcomes variables. The differing conclusions between

studies may be due to a smaller sample for Güzel et al.114 Additionally, the static postural

control outcome variables used in the currently study may be more sensitive compared to

OSI, MLI, and API used by Güzel et al.114

Condition 2 eliminates visual input and static postural control relies on input from

the somatosensory and vestibular systems whereas condition 3 alters somatosensory input

and relies on visual and vestibular input for static postural control.184 No statistical

differences were found for condition 2 between athletes who are D/HoH and athletes who

are hearing for any static postural control outcome variables; however, athletes who are

D/HoH were found to have statistical larger sway than athletes who are hearing for all

condition 3 static postural control outcome variables except for AP CoP RMS. This

suggests that athletes who are D/HoH have a higher reliance on somatosensory

information compared to visual information. In agreement with the results of our study and those of Maheu et al.,99 higher reliance on somatosensory information during postural

control performance has been suggested in individuals with vestibular dysfunction,185

such as some athletes who are D/HoH. Previous authors have suggested an increase in

somatosensory re-organization within the primary auditory cortex compared to visual

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information.186 How individuals who are D/HoH utilize sensory information during static postural control may be different due to plastic changes of the brain. Maheu et al.,99

suggested that individuals with congenital hearing loss relied more heavily on

somatosensory information to maintain postural control compared to individuals who are

hearing, which is consistent with our findings.

In condition 4, participants relied on vestibular function to remain stable during

the static postural control assessment while visual input is eliminated and somatosensory

system is compromised.178 Similar to condition 3, athletes who are D/HoH were found to

have larger sway compared to their hearing counterparts in condition 4 for all static

postural control outcomes except for AP CoP RMS. This may be due to the higher

reliance on somatosensory information,99 as previously described, and/or possible

vestibular dysfunction in some athletes who are D/HoH.13 Vestibular dysfunction may

exist in individuals who are D/HoH due to the intimate relationship between the

vestibular apparatus and their shared neurovascular supply.13 Though the exact

percentage of individuals with vestibular dysfunction in adults who are D/HoH is

unknown, researchers suggest that vestibular dysfunction exists in 30-70% of children

who are D/HoH.187 Additionally, vestibular dysfunction occurring alongside hearing loss

increases when there is profound hearing loss, viral or bacterial infection or if hearing

loss is due to inheritance of specific protein-truncating mutations.88-90 Though the exact extent of hearing loss and etiology of hearing loss was unknown in the population of athletes who are D/HoH in the current study, vestibular dysfunction may be contributing to the differences in static postural control performance between athletes who are D/HoH

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and athletes who are hearing.

The only static postural control outcome that was not statistically different for any

condition between athletes who are D/HoH and athletes who are hearing was AP CoP

RMS. The lack of differences between groups for AP CoP RMS conditions may be due to the body being more sensitive to ML perturbations compared to AP perturbations when the feet are placed together.188 AP CoP RMS may not be a sensitive enough measure to

differentiate static postural control performance between athletes who are D/HoH and

athletes who are hearing.

Though the mCTSIB was designed to assess sensory systems that influence

postural control, the results from the current study suggest that static postural control

performance did not always differ between each condition for each outcome variable for

athletes who are D/HoH and athletes who are hearing. How athletes who are D/HoH and

athletes who are hearing use sensory information and may be different and influence of

lack of differences between certain conditions for certain static postural control

outcomes. Specifically for athletes who are D/HoH, a pattern emerged where there was

no statistically significant differences between conditions 1 and 2 for all outcome

variables except for 95% ellipse sway. This suggests that athletes who are D/HoH may

not rely on visual information for static postural control performance, however, this was

apparent for athletes who are hearing. In contrast, for athletes who are hearing, a pattern

that emerged was that there were no statistically significant differences between

conditions 2 and 3 for all outcome variables except for AP CoP RMS. This suggests that

when one sensory systems is being modified (i.e. visual or somatosensory) postural

103 control performance is similar, however, this was not apparent for athletes who are hearing.

To our knowledge, this is the first study to investigate dynamic postural control between athletes who are D/HoH and athletes who are hearing. Though athletes who are

D/HoH had a longer time-to-stability (1.76±0.94 seconds) compared to athletes who are hearing (1.59±0.55 seconds), these results were not statistically significant. This may be due to all sensory systems being available during the dynamic postural control assessment. Though previous authors suggest sensory system differences such vestibular function183 and increased reliance on somatosensory system99 between individuals who are D/HoH and hearing, athletes who are D/HoH may be able to appropriately perform dynamic tasks as well as their hearing counterparts.

Clinically, it is important for sports medicine professionals to note possible postural control differences between athletes who are D/HoH and athletes who are hearing to help guide rehabilitation and return-to-play decisions. According to the

National Collegiate Athletic Associations’ Concussion Diagnosis and Management Best

Practices, all varsity athletes should undergo baseline concussion assessments.189 The administration of baseline postural control assessments may be beneficial and provide valuable information for the interpretation of post-concussive assessments and allow for a more informed return-to-play decision.190 If athletes who are D/HoH demonstrate differing postural control performance at baseline, comparing post-concussive symptoms to population norms may not be the best practice. This may then influence the management, return-to-play decisions, and overall safety for the athlete.

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Overall, this study provides evidence of static but not dynamic postural control

performance differences between athletes who are D/HoH and athletes who are hearing.

However, there are limitations to note from this study. The level of collegiate athletic competition was different between athletes who are hearing and athletes who are D/HoH and therefore could have influenced the results. Additionally, the hearing status for all participants was self-reported and possibly inaccurate. Lastly, history of cochlear implantation was not controlled for and may have influenced vestibular function and therefore, postural control performance of these athletes. Future research should investigate the use of clinical static and dynamic postural control assessments of athletes

who are D/HoH and influence of history of cochlear implantation surgery on postural

control performance.

Conclusion

The purpose of this study was to compare static and dynamic postural control of

athletes who are D/HoH to athletes who are hearing. Overall, athletes who are D/HoH

demonstrated increase postural sway compared to athletes who are hearing during the

mCTSIB. These findings may be secondary to vestibular dysfunction in some athletes

who are D/HoH, which could lead to an increase in reliance on somatosensory

information, and/or an increased somatosensory reliance independent of vestibular status.

However, there were no differences in dynamic postural control performance between

athletes who are D/HoH and athletes who are hearing during the time-to-stabilization task.

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Chapter 5: Determine the Effect of Hearing Status on Dynamic Visual Acuity Performance of Athletes

Abstract

Background: While assessment of the vestibular system post-concussion has become

integral to return-to-play, the available information on vestibulo-ocular reflex (VOR)

assessment and its association with sports performance and sports-related concussion

remains sparse. Within the population of individuals who are deaf or hard-of-hearing

(D/HoH), vestibular dysfunction may exist secondary to the intimate relationship

between the vestibular apparatus, cochlea, and neurovascular supply.

Purpose: To determine if there is an effect of hearing status on dynamic visual acuity

(DVA) performance of athletes.

Methods: Collegiate athletes who are D/HoH (n=38, 20.89±2.20 yrs., 1.74±0.12 m.,

74.77±17.04 kg.) and university club-level athletes who are hearing (n=38, 20.68±1.32

yrs., 1.76±0.09 m., 77.40±12.75 kg.) volunteered to participate in the study. Participants were assessed using the Bertec Vision Advantage (Bertec Corp., Columbus, OH, USA) baseline visual acuity (BLVA), visual processing time (VPT), and DVA BLVA and VPT were assessed prior to DVA. To assess DVA, the participant sat 5 feet away looking

straight ahead at the laptop screen. The participant’s head was passively rotated in yaw at

2 Hz. An optotype flashed on the screen pointed in one of four directions and the

participant identified the direction of the optotype when it disappeared. If the participant

could not identify the direction, they indicated, “I don’t know.” A wearable, wireless

head tracker was worn by the participant on their forehead that verified the rotation speed

106 and determine when optotypes were presented. Both right and left DVA were assessed with a total of 20 trials per side. The optotype grew larger for a wrong answer and smaller for a correct answer until the software algorithm had determined the participant’s threshold dynamic visual acuity. One-way ANOVAs were performed for all variables.

Alpha level was set a priori p≤0.05.

Results: Hearing status significantly influenced BLVA (F1,74=12.67, p=<0.01) whereby athletes who are D/HoH exhibited poorer BLVA than athletes who are hearing. No significant main effect of hearing status was observed on visual processing time

(F1,74=0.11, p=0.74) and DVA yaw rotation to the left (F1,74=0.09, p=0.76) or to the right

(F1,74=0.72, p=0.40).

Conclusion: Dynamic visual acuity was the same for athletes regardless of hearing status. The VOR mechanism, which primarily serves DVA, may not be sensitively influenced by the potential vestibular dysfunction of some individuals who are D/HoH.

Overall, baseline assessments of DVA of athletes who are D/HoH may not be necessary for preseason assessment.

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Introduction

The assessment of the vestibular and ocular motor systems is becoming an

integral aspect to the management of a sports-related concussion.191 The presence of

vestibular dysfunction following sport-related concussion has been associated with

decreased cognitive performance192 and prolonged recovery.125,129 Up to 50% of

individuals following a sports-related concussion have vestibular-related dysfunction11

leading to a 6.4 times greater risk of protracted recovery12 including increased likelihood

of post-concussion syndrome129 and delay in return to academics.125 This delay in

resolution of vestibular-related symptoms may be secondary to disruption of either the

vestibular-spinal afferent pathway or the vestibular-ocular afferent pathway, which assist

with postural control and visual gaze stability and visual acuity during head movements,

respectively.140,191 Vestibular assessments relative to sport-related concussion may

recognize clinical deficits that other aspects of the multifaceted assessment may overlook,

especially in special populations such as athletes who are deaf or hard of hearing

(D/HoH).

Within the population of individuals who are D/HoH, vestibular dysfunction may

exist due to the intimate relationship between the vestibular apparatus and cochlea,

including similar mechanoreception as well as shared perilymph, endolymph, and

neurovascular supply.13 Currently, there are an estimated 692,00014 school-aged and over

71,00015 post-secondary students who are D/HoH. Many of these students participate in

mainstream school athletics but others participate in athletics at residential schools for the

deaf.42 Athletes who are D/HoH also participate at the collegiate level within the National

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Collegiate Athletic Association (NCAA).44,176 There are also national athletic teams for

the deaf which fall under the USA Deaf Sports Federation. This organization provides oversight to the USA deaf athletic teams and supports them at international competitions such as the Deaflympics.193 Despite the involvement in athletic competition at numerous

competition levels, information regarding vestibular function, specifically vestibular-

ocular reflex performance, is lacking in this population. An understanding of vestibular-

ocular reflex (VOR) performance in this population may assist with post-injury

management in athletes who are D/HoH.

Previous authors have suggested that VOR performance is decreased in some

individuals who are D/HoH.150,194 However to our knowledge, no evidence regarding

VOR function of athletes who are D/HoH exists. Due to potential vestibular dysfunction,

VOR outcomes of athletes who are D/HoH may not accurately reflect that of normative

data. If these possible discrepancies are not accurately identified, it may negatively

influence the management and return-to-play decisions for the athlete who is D/HoH.

The purpose of this study was to determine the effect of hearing status on dynamic visual

acuity (DVA) of athletes. We hypothesized that athletes who are D/HoH will have poorer

DVA performance compared to athletes who are hearing.

Methods

Participants

Participants included 38 collegiate varsity athletes who are D/HoH (20.89±2.20

yrs., 1.74±0.12 m., 74.77±17.04 kg.) and 38 collegiate club level athletes who are hearing

(20.68±1.32 yrs., 1.76±0.09 m., 77.40±12.75 kg.) from two institutions. Athletes who are

109

D/HoH were recruited from the world’s only university designed to be barrier-free for

students who are D/HoH.

Inclusion and Exclusion Criteria

Inclusion Criteria

Exclusion Criteria

• Medically diagnosed concussion within 6 months of study participation • Post-concussion syndrome • Medically diagnosed mental health condition • Medically diagnosed blindness • Pregnancy

Consent and Communication Considerations

Athletes who were D/HoH were given an opportunity to view the consent form in video form interpreted in American Sign Language (ASL). However, all participants were required to sign the paper consent form whether they viewed the ASL interpreted video or not. Additionally, a study member who was fluent in ASL and English was

present during the consent process and all data collections if any participants had

questions or required clarification.

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Questionnaire

Prior to completing the postural control assessments, participants completed a

self-reported questionnaire with items regarding their sex, primary sport participation,

concussion history, and hearing status (Appendix A).

Dynamic Visual Acuity Assessment

VOR was assessed through the DVA test utilizing the Bertec Vision Advantage

(Bertec, Inc, Columbus, OH). If the participant used type of prescriptive corrective

lenses, they were instructed to wear them during testing. In order to assess DVA, the

participants were first assessed for their baseline visual acuity (BLVA) and visual

processing time (VPT). BLVA acted as a baseline reference for when the head is

stationary, while VPT ensured that the participants could identify the test stimuli

appropriately during the DVA assessment. For baseline visual acuity, the participant sat 5

feet away looking straight ahead at the laptop screen. A blocked-letter letter “E” (called

an optotype) flashed on the screen pointed in one of four directions (up, down, left, or

right). The participant was asked to identify the direction of the optotype when it

disappeared from the screen. If the participant could not identify the direction, they were

asked to indicate, “I don’t know.” All answers were entered by a research team member into the computer via a remote. For BLVA, the optotype grew larger for a wrong answer and smaller for a correct answer until the software algorithm determined the participant’s baseline visual acuity. The same methodology described above was used to assess VPT

except for incorrect answers, the optotype stayed on the screen for more time and for

111 correct answers, the optotype stayed on the screen for less time. The shortest VPT allowed by the device was 30 milliseconds.

DVA is a behavioral assessment of the VOR in response to rotation head stimuli that measures participant’s threshold acuity. To assess DVA, the patient again sat 5 feet away from the laptop looking straight ahead. The research member stood behind the participant and passively rotated the head in yaw rotation around an earth-vertical axis at

2 Hz. The participant was asked to identify an optotype that was displayed momentarily on the computer screen at the participant’s eye level when the participant’s head is rotating. The optotype rotated randomly in one of four directions for each trial. A wearable, wireless head tracker was worn by the participant on their forehead that verified the rotation speed by the research team member and also determined when the optotype appeared on the computer screen. The participant reported the direction of the optotype to the research team member (up, down, left, right). The participant may also respond “I don’t know.” All answers were entered by a research team member into the computer via a remote. Both right and left DVA was assessed with a maximum of 20 trials performed for each side. The optotype would grow larger for a wrong answer and smaller for a correct answer until the software algorithm had determined the participant’s

DVA.

Statistical Analysis

Descriptive statistics were used to describe the distributions of participant demographics and chi-square tests were performed to assess the association between

112 participant demographics and hearing status. One-way ANOVAs were used to compare baseline visual acuity, visual processing time, and DVA performance between athletes who are hearing and athletes who are D/HoH. DVA was determined by subtracting the baseline visual acuity logarithm of the minimum angle of resolution (LogMAR) score from the DVA logMAR score. All statistical analyses were performed with Stata/IC

(StataCorp. 2017. Stata Statistical Software: Release 15. College Station, TX: StataCorp

LLC). A statistical significance level was set at α < 0.05.

Result

Demographics for the entire sample by hearing status are presented on Table 17.

The sample included 27 males who were hearing, 11 females who were hearing, 31 males who were D/HoH and 7 females who were D/HoH. Hearing status was not significantly associated with sex (χ2 (1, n=76) = 1.16, p=0.28), age (χ2 (1, n=76) <0.01, p=1.00), or concussion history (χ2 (1, n=76) = 0.63, p=0.43). However, hearing status was significantly associated with year in school (χ2 (4, n=76) = 21.95, p<0.01) and sport (χ2

(9, n=76) = 54.85, p<0.01).

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Table 17. Characteristics of participants Deaf or Hard- Hearing of-Hearing p-value n (%) n (%) Sex Male 27 (71.05) 31 (81.58) 0.28 Female 11 (28.95) 7 (18.42) Age 18-21 26 (68.42) 26 (68.4) 1.00 22-28 12 (31.58) 12 (31.58) Year in School First Year 4 (10.53) 15 (39.47) Second Year 4 (10.53) 13 (34.21) Third Year 10 (26.32) 4 (10.53) <0.01 Fourth Year 17 (44.74) 4 (10.53) Fifth Year or Greater 3 (7.89) 2 (5.26) Sport Soccer 5 (13.16) 14 (35.84) <0.01 Basketball 0 (0.00) 3 (7.89) Softball 2 (5.26) 1 (2.63) Baseball 15 (39.47) 1 (2.63) Football 0 (0.00) 12 (31.58) Track and Field 0 (0.00) 6 (15.79) Swimming 0 (0.00) 1 (2.63) Rugby 7 (18.42) 0 (0.00) Hockey 5 (13.16) 0 (0.00) Ultimate Disc 4 (10.53) 0 (0.00) Concussion History Yes 11 (28.95) 8 (21.05) 0.43 No 27 (71.05) 30 (78.95) Note: p-value from chi-square test of independence

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There was a statistically significant effect of hearing status on baseline visual acuity

(F1,74=12.67, p<0.01). There was no statistically significant effect of hearing status on visual processing time (F1,74=0.11, p=0.74). There was no statistically significant effect hearing status on DVA yaw rotation to the right (F1,74=0.72, p=0.40) or the left (F1,74=0.09, p=0.76) (Table 18).

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Table 18. Dynamic Visual Acuity of Athletes who are Hearing and Deaf or Hard- of- Hearing Deaf or Hearing Hard-of-Hearing p-value Mean (SD) Mean (SD) Baseline Visual Acuity (BLVA) -0.21 (0.63) -0.12 (0.14) <0.01 Visual Processing Time (VPT) 31.71 (4.58) 32.11 (5.68) 0.74 Right Dynamic Visual Acuity (DVA) -0.09 (0.18) -0.10 (0.99) 0.40 Left Dynamic Visual Acuity (DVA) -0.11 (0.87) -0.13 (0.11) 0.76 Note: p-value from one-way ANOVAs; BLVA and DVA values are in logMAR units; VPT are in milliseconds; VPT had a minimum score of 30 milliseconds

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Descriptive statistics for athletes who are D/HoH are listed on Table 19. The subsample included 12 males who were hard-of-hearing, 0 females who are hard-of-hearing, 19 males who are deaf, and 7 females who are deaf. Hearing loss status was significantly associated with sex

(χ2 (1, n=38) = 3.96, p=0.04), time of hearing loss (χ2 (1, n=38) = 7.44, p=0.02), history of

cochlear implant surgery (χ2 (1, n=38) = 6.26, p=0.01), right side degree of hearing loss (χ2 (1,

n=38) = 11.58, p=0.02), and left side degree of hearing loss (χ2 (1, n=38) = 15.60, p<0.01).

Additionally, there was no statistically significant effect of hearing loss status on BLVA

(F1,38=3.24, p=0.08), VPT (F1,38=0.39, p=0.54), or DVA yaw rotation to the right (F1,38=0.30,

p=0.59) or to the left (F1,38=0.30, p=0.51) (Table 20).

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Table 19. Characteristics of deaf and hard-of-hearing participants Hard-of-Hearing Deaf p-value n (%) n (%) Sex Male 12 (100.00) 19 (73.08) 0.04 Female 0 (0.00 7 (26.92) Time of Hearing Loss Before Birth 4 (33.33) 16 (61.54) After Birth 7 (58.33) 4 (15.38) 0.02 Unknown 1 (8.33) 6 (23.08) Cochlear Implant Yes 0 (0.00) 10 (38.46) 0.01 No 12 (100.00) 16 (61.54) Degree of Hearing Loss (Right) Unknown to Participate 5 (41.67) 13 (50.00) Normal (-10-15 dB) 0 (0.00) 0 Slight (16-25 dB) 1 (8.33) 0 Mild (26-40 dB) 2 (16.67) 0 0.02 Moderate (41-55 dB) 1 (8.33) 0 Moderately Severe (56-70 dB) 2 (16.67) 2 Severe (71-90 dB) 1 (8.33) 11 Degree of Hearing Loss (Left) Unknown to Participate 5 (41.67) 13 (50.00) Normal (-10-15 dB) 0 (0.00) 0 (0.00) Slight (16-25 dB) 2 (16.67) 0 (0.00) Mild (26-40 dB) 1 (8.33) 0 (0.00) <0.01 Moderate (41-55 dB) 2 (16.67) 0 (0.00) Moderately Severe (56-70 dB) 2 (16.67) 2 (7.69) Severe (71-90 dB) 0 (0.00) 11 (42.31) Note: dB = decibel p-value from chi-square test of independence

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Table 20. Dynamic Visual Acuity Scores of Athletes who are Deaf and Hard-of- Hearing Hard-of-Hearing Deaf p-value Mean (SD) Mean (SD) Baseline Visual Acuity (BLVA) -0.06 (0.18) -0.15 (0.11) 0.08 Visual Processing Time (VPT) 31.25 (4.33) 32.50 (6.24) 0.54 Right Dynamic Visual Acuity (DVA) -0.14 (0.09) -0.12 (0.12) 0.59 Left Dynamic Visual Acuity (DVA) -0.08 (0.71) -0.10 (0.11) 0.51 Note: p-value from one-way ANOVAs; BLVA and DVA values are in logMAR units; VPT are in milliseconds; VPT had a minimum score of 30 milliseconds

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Discussion

DVA of collegiate athletes who are D/HoH is lacking in the literature.

Understanding DVA performance in athletes who are D/HoH may assist in rehabilitation

programs, concussion management, and return-to-play decisions following injury. This study reported DVA performance of athletes who are D/HoH and athletes who are hearing using a computerized DVA assessment. Differences were observed in BLVA between athletes who are D/HoH and athletes who are hearing; however, no differences were observed in VPT or DVA performance between athletes who are D/HoH and athletes who are hearing. Further analysis of a subsample of athletes who are D/HoH revealed that there were no statistically significant differences in BLVA, VPT, or DVA between athletes who are deaf and those who are hard-of-hearing.

The results of the BLVA assessment were compared to DVA in all participants.

Our findings suggest that hearing status had an effect on BLVA with athletes who are

D/HoH having poorer BLVA compared to athletes who are hearing. Although there were differences between groups, both groups demonstrated normal visual acuity or corrected- to-normal visual acuity, which is generally accepted as negative LogMAR values.195

Though there is a paucity in the literature on static visual acuity in athletes who are

D/HoH, static visual acuity assessments are often used as a screen when performing

visual performance assessments. Sladen et al.157 screened static visual acuity for adults

who are deaf and hearing. Though they did not perform any additional analyses between

groups, each group did demonstrate normal or corrected-to-normal visual acuity.157

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Additionally, a study by Codina et al.196 investigated the peripheral vision development

of children who are deaf and hearing. They used static visual acuity as a screen for their

study and found that all participants regardless of hearing loss had a minimum 0.200

LogMAR units.196

VPT in the current study was used to ensure that participants could process the

optotype stimuli quickly enough for the DVA protocol. It should be noted that the

shortest VPT allowed by the device was 30 milliseconds. Due to this, direct VPT

comparisons between athletes who are D/HoH and athletes who are hearing should be

interpreted with caution. It is possible that if the device allowed, one group may have

demonstrated superior VPT, however, this was not possible with the device used in the

current study. Though there is a paucity of literature on VPT with individuals who are

D/HoH, there has been related literature on numerous assessments related to visual

processing demonstrating varying results.152,156,157,159,161,197-201 Both individuals who are

D/HoH152,156,157,197,201 and individuals who are hearing156,161,198,199 have demonstrated

superior visual processing. The differences in results between studies seems to stem from

improved selective visual attention158,202 and use of global perceptual strategies of

individuals who are D/HoH, whereas individuals who are hearing who are more

advantageous in using analytical perceptual strategies.201

The findings of this research suggest that there are no average differences in DVA performance between athletes who are D/HoH and athletes who are hearing. There is a minimal amount of literature regarding DVA performance in adults who are D/HoH.

Nakajima et al.123 investigated DVA performance of athletes who are D/HoH at the

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Deaflympic level. Their findings suggest that DVA scores from individuals who are

hearing were poorer on average compared to athletes who are D/HoH.123 However, it

should be noted that the athletes used who were hearing, “engaged in sports,” without

additional clarification from the authors on the extent of their sport participation.123

Unlike the current study, Nakajima et al.123 used a different device (HT-10, Kowa Co.

Ltd.) to assess DVA. Also, the protocol Nakajima et al.123 used was different where the

participants head was immobilized and the Landolt ring moved horizontally on a

semicircular screen. The participant would then identify the break in the Landolt ring and

that rate was recorded.123 Due to the differences in methodology and level of athletic

competition, caution should be taken when comparing results of the current study and

Nakajima et al.123

The majority of the available literature in individuals who are D/HoH on DVA

performance is with children. Children who are D/HoH have been found to have reduced

DVA on average compared to children who are hearing.122,203-205 One possible

explanation suggested by previous authors is that vestibular function of individuals with deafness does not mature until approximately 9 years of age.206,207 Though this supports the current study of athletes who are D/HoH and athletes who are hearing, other factors such as the influence of sport participation and use of ASL may also have an influence on

DVA performance.

It is possible that participation in sport may aid the development and sustainability of DVA performance in athletes who are D/HoH. Previous authors have suggested that individuals who participate in sport have superior DVA performance compared to

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individuals who do not.208 It is possible that the participation in sport of athletes who are

D/HoH, improves their DVA performance to that of the level of their hearing

counterparts. Additionally, many individuals who are D/HoH use ASL as their primary

mode of communication, which is a visuospatial language.176,209 Due to the visuospatial

nature of ASL,152 it is possible that this may influence DVA performance of athletes who are D/HoH. These two factors may assist athletes who are D/HoH have improved DVA

performance compared to non-athletes and non-signers who are D/HoH to a comparable

level of athletes who are hearing.

Our results suggest there are no statistically significant differences in DVA

performance between athletes who are deaf and athletes who are hard-of-hearing. To the

authors’ knowledge, there is no current literature investigating the influence of degree of

hearing loss on DVA performance. However, our results are in contrast of previous

literature that suggest the greater the degree of hearing loss, the greater the degree of

vestibular dysfunction,210 which is apparent in previous postural control literature of

individuals who are D/HoH.151 The current study had the participants self-report their degree of hearing loss, which may not have been accurate and thus influenced the comparison of DVA performance between athletes who are deaf and athletes who are hard-of-hearing.

Clinically, is it important for sports medicine professionals to note that there may not be differences in average DVA performance between athletes who are D/HoH and athletes who are hearing. While it may be important to have baseline outcomes of other tasks such as postural control211 and neurocognitive assessments212 in athletes who are

123

D/HoH, sports medicine professionals may be able to use existing normative data to

compare post-injury DVA scores. If using normative data to compare DVA outcomes to

athletes who are D/HoH, sports medicine professionals should take note where the

normative data originates from and be cautious if comparing between different levels of

competition or sport.

Overall, this study provides evidence that there are no statistically significant

differences between DVA performance in athletes who are D/HoH and athletes who are

hearing. Additionally, when examining a subsample of our participants, no DVA

performance differences were found between athletes who are deaf and athletes who are

hard-of-hearing. However, there are limitations to note from this study. The level of

competition was different between athletes who are hearing and athletes who are D/HoH,

which could have impacted the results. Additionally, hearing status was self-reported for

all participants and therefore, could have been inaccurate. Lastly, previous authors have

suggested sport activity can influence DVA performance,139,208,213-217 however, due to the

small sample size and a large distribution of sport participation, sport was not accounted

for in the analysis. Future research should take objective measures of hearing loss in order to look at the impact of degree of hearing loss on DVA. Additionally, future research should investigate the impact of sport participation, use of ASL and history of

cochlear implantation surgery on DVA of athletes who are D/HoH.

Conclusion

The purpose of this study was to determine if there are differences in VOR

function of athletes who are hearing and athletes who are D/HoH as assessed by DVA.

124

There were no statistically significant differences in DVA performance between athletes

who are D/HoH and athletes who are hearing. Additionally, there were no statistically

significant differences in DVA performance between athletes who are deaf and athletes

who are hearing. These findings suggest that baseline DVA scores may not be necessary

for athletes who are D/HoH and post-injury comparison to normative data may be appropriate

125

Chapter 6: Conclusion and Future Research Considerations

Conclusion

The overall objective of this research was to gain a better understanding of

vestibular function of athletes who are deaf or hard-of-hearing (D/HoH). The rationale behind the proposed research was to characterize vestibular function of individuals who are D/HoH to ultimately guide vestibular-related interventions, concussion management, and return-to-sport guidelines. The major findings from this study include that concussion rates are similar in sex comparable sports between athletes who are D/HoH and athletes who are hearing. Additional major findings include that baseline postural control performance but not baseline dynamic visual acuity (DVA) were different between athletes who are D/HoH and athletes who are hearing.

Chapter 3 established similarities and differences in epidemiology of concussion between National Collegiate Athletic Association (NCAA) Division III athletes who are

D/HoH and athletes who are hearing. The results of this chapter indicate that concussion rates are higher for athletes who are hearing compared to athletes who are D/HoH in all sports investigated. Athletes, specifically football athletes and male athletes, who are hearing had a higher rate of concussion compared to athletes who are D/HoH. However, there were no differences in concussions rates among female athletes and sex comparable sports between hearing statuses.

126

Chapter 4 determined the effect of hearing status on static and dynamic postural

control performance of athletes. Results from this chapter indicate that there was an effect

of hearing status on static postural control performance. Athletes who are D/HoH

demonstrated increased sway for conditions 1, 3, and 4 of the modified clinical test of

sensory interaction and balance (mCTSIB) for total, anterior-posterior (AP), and medial-

lateral (ML) center-of-pressure (CoP) excursion, AP and ML CoP range, ML RMS, and

sway area. However, there were no differences between static postural control

performance of athletes who are D/HoH and athletes who are hearing during condition 2

of the mCTSIB for total, anterior-posterior (AP), and medial-lateral (ML) center-of-

pressure (CoP) excursion, AP and ML CoP range, ML RMS, and sway area. For AP

RMS, there were no static postural control performance differences between groups.

When examining the effect of hearing status on dynamic postural control during a jump- landing task, no differences were found between groups in regards to time-to- stabilization.

Chapter 5 determined the effect of hearing status on vestibulo-ocular reflex performance via dynamic visual acuity (DVA) of athletes. Results from this chapter indicate that hearing status has an effect on baseline visual acuity (BLVA) of athletes.

However, no effect of hearing status was found for either visual processing time (VPT) or

DVA in athletes. Additionally, an analysis of a subsample of athletes who are D/HoH suggests that there are no differences in BLVA, VPT, or DVA between athletes who are hard-of-hearing and athletes who are deaf. Given the similar concussion rates in sex comparable sports, it is essential for athletes who are D/HoH to have appropriate timing

127

and interpretation of vestibular-related assessments to ultimately guide vestibular-related interventions, concussion management, and return-to-sport guidelines.

Future Directions

Future research should focus on the steps necessary to achieve our long-term goal

to optimize concussion management in athletes who are D/HoH. To achieve this goal,

future research should focus on investigating concussion epidemiology and postural

control performance of athletes who are D/HoH at different levels of competition

including high school and national teams. Additionally, examining differences between

athletes who are D/HoH and athletes who are hearing using clinical postural control

assessment should be used. In addition, future research should investigate athletes who

are D/HoH in addition to performing a comprehensive DVA assessment including yaw

rotation, pitch, and roll-tilt.

Furthermore, future research should focus on investigating vestibular function of

athletes who are D/HoH following acute concussion and also include the development of

recovery trajectories for vestibular-related symptoms including postural control and

DVA. In addition to vestibular-related concussion management, future research should also focus on other aspects of concussion management including neurocognitive assessments, vestibular perceptual thresholds, and reaction time. The above future research should be conducted across all levels of sports competition including youth, high

school, collegiate, and elite.

128

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Appendix A. Questionnaire

Subject ID: ______Age: ______

Please answer the questions below to the best of your ability.

1. What is your sex? ☐ Male ☐ Female

2. What is your year in school? ☐ 1st year ☐ 2nd year ☐ 3rd year ☐ 4th year ☐ 5th year

3. What sport do you primarily participate in? ______

4. How long have you been participating in your primary sport? ______

5. Do you competitively play a second sport? ☐ Yes ☐ No

6. Do you have a history of concussions? ☐ Yes ☐ No

7. I consider myself… ☐ Hearing ☐ Hard-of-hearing ☐ Deaf

Please only answer questions 8, 9, and 10 if you answered hard-of-hearing or deaf for answer 7.

8. When did you lose your hearing? ☐ Before birth 155

☐ After birth ☐ I don’t know

9. Do you have a cochlear implant? ☐ Yes ☐ No

10. If you have hearing loss, please choose the degree of hearing loss in each ear. ☐ I do not know my degree of hearing loss

Degree of Hearing Loss Range in Left Right Hearing Loss Decibels

☐ ☐ Normal -10 to 15

☐ ☐ Slight 16 to 25

☐ ☐ Mild 26 to 40

☐ ☐ Moderate 41 to 55

Moderately ☐ ☐ 56 to 70 Severe

☐ ☐ Severe 71 to 90

156