University of Tennessee Health Science Center UTHSC Digital Commons Theses and Dissertations (ETD) College of Graduate Health Sciences 12-2020 Effect of Sound Source Location and Spatial Hearing on the Vestibulo-Ocular Reflex (VOR) Mary Easterday University of Tennessee Health Science Center Follow this and additional works at: https://dc.uthsc.edu/dissertations Part of the Speech and Hearing Science Commons, and the Speech Pathology and Audiology Commons Recommended Citation Easterday, Mary (https://orcid.org/0000-0002-8744-475X), "Effect of Sound Source Location and Spatial Hearing on the Vestibulo-Ocular Reflex (VOR)" (2020). Theses and Dissertations (ETD). Paper 529. http://dx.doi.org/10.21007/etd.cghs.2020.0527. This Dissertation is brought to you for free and open access by the College of Graduate Health Sciences at UTHSC Digital Commons. It has been accepted for inclusion in Theses and Dissertations (ETD) by an authorized administrator of UTHSC Digital Commons. For more information, please contact [email protected]. Effect of Sound Source Location and Spatial Hearing on the Vestibulo-Ocular Reflex (VOR) Abstract Accurate measurement of the vestibulo-ocular reflex (VOR) is imperative in differential diagnosis of vestibular disorders and balance function. However, the assessment protocol faces a number of limitations, including the need to control for extra- vestibular sensory factors such as hearing. Previous research has shown that the use of an auditory stimulus can have a significant effect on functional measures of balance, and many have contributed effects to be the result of spatial hearing. However, no studies have directly assessed the effect of speaker location on the VOR nor investigated correlations of functional spatial hearing with the VOR. Therefore, the aims of this study were to 1) assess the effect of speaker location on the VOR and 2) investigate if spatial hearing abilities are correlated with the strength of the VOR. A between subjects repeated measures design was utilized with a child group (age 6-9 years) and an adult group (18-40 years). The rationale of the two groups was to compare differences in a group with underdeveloped localization abilities (child) and a group with matured localization abilities (adult). A total of 22 children and 23 adults participated in this study. Localization ability was measured using the root mean square (RMS) error method. VOR gain was measured using the rotational chair test at a rate of .08 Hz in the following auditory conditions: silent (insert earphones turned off), insert earphones turned on, external speaker at 0° azimuth rotating with participant, and external stationary speaker. Order of testing was randomized to control for any order effects. An independent samples t-test confirmed a significant difference in RMS error between groups with the child group performing worse than the adults. Subsequent multivariate analysis of variance indicated a significant effect for speaker location with the external moving speaker having significantly lower gain and the external stationary speaker having significantly increased gain for both child and adult groups. Correlations were run for both groups for both fixed and moving speaker conditions. No correlation was seen in either condition for the child group, however, a positive correlation was seen for both conditions for the adult group, meaning as RMS error increased so did VOR gain. These results indicate the possible need to control for environmental auditory stimulus location when undergoing vestibular assessment. However, further studies need to be performed to corroborate the evidence presented. Document Type Dissertation Degree Name Doctor of Philosophy (PhD) Program Speech and Hearing Science Research Advisor Patrick Plyler, PhD Keywords Assessment, Vestibular Subject Categories Communication Sciences and Disorders | Medicine and Health Sciences | Speech and Hearing Science | Speech Pathology and Audiology This dissertation is available at UTHSC Digital Commons: https://dc.uthsc.edu/dissertations/529 UNIVERSITY OF TENNESSEE HEALTH SCIENCE CENTER DOCTORAL DISSERTATION Effect of Sound Source Location and Spatial Hearing on the Vestibulo-Ocular Reflex (VOR) Author: Advisor: Mary Easterday Patrick Plyler, Ph.D. A Dissertation Presented for The Graduate Studies Council of The University of Tennessee Health Science Center in Partial Fulfillment of the Requirements for the Doctor of Philosophy degree from The University of Tennessee in Speech and Hearing Science: Audiology College of Graduate Health Sciences December 2020 Copyright © 2020 by Mary Easterday. All rights reserved. ii DEDICATION This dissertation is dedicated to all those who supported and encouraged me through this arduous process. Most of all, this goes to my family at home and my family at the University of Tennessee. iii ACKNOWLEDGEMENTS I would like to acknowledge Dr. Patrick Plyer for his invaluable mentorship and assistance; as well as committee members Drs. Ashley Harkrider, Patti Johnstone, James Lewis, Jefferey Fairbrother, and Devin McCaslin. I would also like to acknowledge Dr. Steven Doettl as the vestibular consultant and for his contribution to the research reported here. iv ABSTRACT Accurate measurement of the vestibulo-ocular reflex (VOR) is imperative in differential diagnosis of vestibular disorders and balance function. However, the assessment protocol faces a number of limitations, including the need to control for extra- vestibular sensory factors such as hearing. Previous research has shown that the use of an auditory stimulus can have a significant effect on functional measures of balance, and many have contributed effects to be the result of spatial hearing. However, no studies have directly assessed the effect of speaker location on the VOR nor investigated correlations of functional spatial hearing with the VOR. Therefore, the aims of this study were to 1) assess the effect of speaker location on the VOR and 2) investigate if spatial hearing abilities are correlated with the strength of the VOR. A between subjects repeated measures design was utilized with a child group (age 6-9 years) and an adult group (18-40 years). The rationale of the two groups was to compare differences in a group with underdeveloped localization abilities (child) and a group with matured localization abilities (adult). A total of 22 children and 23 adults participated in this study. Localization ability was measured using the root mean square (RMS) error method. VOR gain was measured using the rotational chair test at a rate of .08 Hz in the following auditory conditions: silent (insert earphones turned off), insert earphones turned on, external speaker at 0° azimuth rotating with participant, and external stationary speaker. Order of testing was randomized to control for any order effects. An independent samples t-test confirmed a significant difference in RMS error between groups with the child group performing worse than the adults. Subsequent multivariate analysis of variance indicated a significant effect for speaker location with the external moving speaker having significantly lower gain and the external stationary speaker having significantly increased gain for both child and adult groups. Correlations were run for both groups for both fixed and moving speaker conditions. No correlation was seen in either condition for the child group, however, a positive correlation was seen for both conditions for the adult group, meaning as RMS error increased so did VOR gain. These results indicate the possible need to control for environmental auditory stimulus location when undergoing vestibular assessment. However, further studies need to be performed to corroborate the evidence presented. v TABLE OF CONTENTS CHAPTER 1. INTRODUCTION .....................................................................................1 CHAPTER 2. LITERATURE REVIEW .........................................................................3 Basic Vestibular Anatomy and Physiology .....................................................................3 Peripheral Vestibular System .......................................................................................3 Central Vestibular System ...........................................................................................4 Vestibulo-Ocular Reflex ..............................................................................................5 Vestibular Assessment Utilizing the VOR...................................................................6 Spatial Hearing ................................................................................................................7 Duplex Theory .............................................................................................................7 Root Mean Square Error ..............................................................................................8 Visual Suppression ..........................................................................................................8 Effects of Non-Visual Stimulation ..................................................................................8 Spatial Hearing and Balance Function ...........................................................................13 Sound Stimulation and Functional Tests of Balance .................................................13 Vestibulo-Spatial Interaction .....................................................................................16 Current Study Aims .......................................................................................................18