Crossmodal Duration Perception in Aging Adults

University of Nevada, Reno

Crossmodal duration perception in aging adults

A thesis submitted in partial fulfillment of the requirements for the degree of

Bachelor of Science in Neuroscience and the Honors Program

Dustin W. Dutcher

Dr. Fang Jiang, Thesis Advisor

May, 2018

Abstract Temporal perception in the elderly population is impaired in unisensory and multisensory contexts. How aging affects one aspect of temporal processing, duration perception, remains unknown. In young adults, the auditory modality has a much higher resolution of duration discrimination over the visual system. The auditory system also has the capability to influence visual duration perception due to the dominance of the auditory modality in temporal discriminability. This influence diminishes with increasing duration difference between the auditory and visual stimuli. This project aimed to examine whether audition dominates vision in duration perception in a similar way in the elderly. Due to wider temporal windows that older adults have for other temporal perceptions, older adults should experience these influence effect over greater duration differences than young adults. The results of this project concluded that age was not a significant factor determining the extent of auditory influences on visual duration perception. The alignment of auditory and visual stimuli was the greatest factor determining influence effects.

Acknowledgments

First and foremost, I would like to thank Allie Scurry for her extreme involvement in this project from start to finish. Without her help, advice, and knowledge, I would have spent a lot less time in a dark room with older individuals.

I would also like to thank Dr. Fang Jiang for driving this project in a positive direction, thoroughly editing every aspect of this thesis and project, and allowing me to spend a lot of time in a dark room with older individuals.

I must also thank Dr. Valentine for helping every student pursue and complete an honors thesis. Thank you for being by my side since day one, in a hospital, after an unfortunate accident on the Capture the Flag Field.

Finally, thank you to Honors Undergraduate Research Award committee for financially supporting this project.

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Table of Contents

Abstract……………………………………………………………..…………………………i Acknowledgments……………………………………………………………………………ii Table of Contents……………………………………………………………………………iii List of Figures………………………………………………………………………………..iv Introduction…………………………………………………………………………………..1 Literature Review……………………………………………………………………………8 Methodology…………………………...……………………………………………………17 Overview……………………………………………………………………………..17 Participants……………………………………………………………………..……17 Apparatus and Stimuli……………………………………………………………….18 Experiment 1 – Visual, Auditory, & Auditory-Visual JND Thresholds……………...18 Experiment 2 – Auditory Influence on Visual Duration Perception…………………21 Experiment 3 – Expansion and Compression Effects………………………………..24 Results……………………………………………………………………………………….27 Experiment 1 – Visual, Auditory, & Auditory-Visual JND Thresholds …….……….27 Experiment 2 – Auditory Influence on Visual Duration Perception…………………28 Experiment 3 – Expansion and Compression Effects………………………………..32 Discussion…………………………………………………………………………………...36 Experiment 1 – Visual, Auditory, & Auditory-Visual JND Thresholds ………….….36 Experiment 2 – Auditory Influence on Visual Duration Perception…………………37 Experiment 3 – Expansion and Compression Effects………………………………..39 Conclusions………………………………………………………………………………….41 References…………………………………………………………………………………...44

List of Figures

Figure 1. Visual representation of experiment 1 design………………………………….20 Figure 2. Visual representation of experiment 2 design………………………………….23 Figure 3. Visual representation of experiment 3 design………………………………….26 Figure 4. Mean thresholds at 82% for the visual, auditory, and audiovisual modalities………………………………………………………28 Figure 5. Modality influence on duration perception…………………………………….29 Figure 6. Expansion and compression effects of young and older adults……………….33 Figure 7. Linear regression analysis for effect of alignment and age…………………...35

Introduction

Time is an important, integral part of everyday life. People sense the passing of time and use that perception to perform important tasks such as understanding speech, driving, and walking. Time perception is the sense of a time characteristic of an element, whether that characteristic is the duration an element lasts or the order which different elements appear.

Whereas all of the senses - sight, smell, taste, touch and audition - have specific receptors to detect their respective stimuli, accurate perception of passing time is normally integrated from different systems. For example, when the brain is sensing a time from the seconds to minutes scale, dopamine (a neurotransmitter typically associated with reward and pleasure pathways) plays a role in the basal ganglia in judging these time durations (Meck, 1996).

Oscillating frequencies from the brain’s cortex are detected in the basal ganglia and related to previously stored patterns as memories (Meck, 1996). The basal ganglia is a small region in the brain that mainly functions to initiate and regulate movement; however, these oscillating frequencies are stored in a region known as the hippocampus. Different processes in other regions of the brain, such as the cerebellum, are associated with shorter, sub-second intervals

(Lee et al., 2007). The cerebellum is the “small brain” on the posterior side of the brain, whose main function is to refine motor movement signals before the signals are sent to their appropriate locations. The physiological processes of both longer and shorter time perception have a basis in a metaphorical, internal ticking clock that subconsciously keeps track of time.

Differences in the physical location of time and duration perception in the brain are only a fraction of what makes research in the field of time perception so expanse.

Time perception is central to virtually all psychological phenomena. Time perception is linked to behavior and memory, physiological processes, motor functions, event length 2 distortions, and dominant temporal resolutions (sensitivities) in specific senses. An underlying factor to all of time perception research is how well certain senses can discriminate time durations. In young adults with normal vision, duration perception by the visual system is relatively poor; among this population, the visual system has been proven to be more reliable in spatial resolution over temporal (Witten & Knudsen, 2005). The visual system is better suited to determine the location of objects over the auditory system because eyes are mobile and vision is binocular, allowing for depth perception. Ears are stationary and can only receive information on a single horizontal plane, even when the head tilts or rotates. For example, while walking on a pier by the ocean, one might hear the horn from a large vessel. The individual is able to determine that the sound came from the left side, but probably would not be able to determine precisely how far out the ship is, until one turned their head and judged the distance with their eyes. While the visual system can better detect positional or spatial information, the auditory system is much more in tune with information regarding time.

The auditory system is dominant in almost every aspect of time perception, meaning it provides a more reliable representation of time information for the brain to interpret. While light waves travel significantly faster than sound waves, the neurological processing time is significantly longer for visual information than auditory (50ms versus 10ms respectively)

(Keetels & Vroomen, 2012). Information reaches eyes quicker than ears, but the brain knows the quickest route for the auditory information to be processed and interpreted faster than the route for the visual information. It would be very difficult to determine the relative speed of a passing car without the help of the auditory system. While the visual system can detect and recognize images in as little as 13 milliseconds (ms), the brain has a difficult time 3 understanding the physical amount of time that the eyes detected, whether it is 13 ms, or 30 ms, or 100 ms (Potter, 2012). In other words, eyes can detect 13 ms, but because people do not typically use these timescales, it would be impossible to count to 13 ms in one’s head

(Potter, 2012).

The auditory modality has routinely been shown to be dominant in temporal processing and discrimination tasks (Witten & Knudsen, 2005). Discrimination threshold tasks are a common way among researchers to determine the point where an individual can no longer tell the difference between two objects, called the just-noticeable-difference (JND).

The difference that is being measured is determined by the researchers and what their question entails. These differences can be weight, time, frequency, amplitude, intensity, or anything at all. The duration discrimination thresholds for auditory stimuli (tones or beeps) that last less than a second tend to be significantly lower than sub-second visual stimuli

(flashes or images), and this effect usually persists for durations lasting up to 10 seconds

(Witten & Knudsen, 2005). People are generally able to determine the difference between a beep that lasts 500 ms and a beep that lasts 580 ms; however, differentiating between an image that lasts 500 ms and an image that lasts 580 ms is much more difficult (Witten &

Knudsen, 2005). The auditory modality’s ability to distinguish this 80 ms difference gives it a lower threshold than the visual modality. In the case of this project, lower thresholds are associated with having a higher resolution.

In the real world, the brain does not rely solely on just one modality for information.

The brain constantly integrates information from the two senses (crossmodal or multisensory integration) to get a more accurate spatial and temporal representation of the world.

Multisensory integration provides complementary information about an object or event: a car 4 passing in the fast lane, understanding speech when having a face-to-face conversation, or hitting a baseball. The integration of senses to complete a story is especially helpful when there is a lack of reliable information from one sense or a conflict between the senses. In addition to integration, the brain also uses information from one dominant sense to influence the perception of another sense (crossmodal influence). The brain depends on the more dominant modality to fill in the gaps, which is helpful in many cases but can also lead to a distorted perception of reality.

In the case of presenting co-occurring auditory and visual stimuli, whether it be a spatial or temporal task, the brain relies on the dominant modality to influence a perception

(Klink, Montijn, & van Wezel, 2011). Audiovisual crossmodal influence effects have interesting outcomes on perceived duration of events. For example, when a light flash and a tone are played separately for the same amount of time, the sound is subjectively perceived as longer than the light flash (Walker & Scott, 1981). Interestingly, when young adults are presented with a tone and a flash simultaneously, and the tone is played longer or shorter, an expansion and compression effect on the perceived visual duration occurs, respectively. The auditory information takes over the duration perception of the visual information and the brain thinks that the image lasted longer than it actually did due to the extended duration of the beep. A compression effect occurs when the image appears much shorter than it physically is because the image is paired with a short sound. An expansion effect occurs when the image appears to last longer than the image actually is when the image is paired with a longer beep. Klink et al. (2011) suggested that a fixed visual duration of 500 ms elicits the greatest expansion effect when paired with an auditory stimulus that lasts between

650-900 ms. Similarly, the greatest compression effects are seen when a visual duration of 5

500 ms is paired with an auditory stimulus of 100-350 ms (Klink, Montijn, & van Wezel,

2011).

Studies on crossmodal duration perception usually recruit the healthy, young adult population. Older individuals are typically not included due to concerns of their age-related changes in sensory abilities. Vision impairments are typical with aging, with the pupil reducing to a third of its size by age 60, reducing overall visual acuity, among many more serious visual problems (Kasthurirangan & Glasser, 2006). Hearing loss as a result of age is inevitable, as delicate nerve networks in the inner ear degrade (Ostroff et al., 2003). Natural declines in the auditory system have been offered as reasons for speech perception and discrimination problems in the older adult population due to impaired time perception

(Ostroff et al., 2003). Due to the lack of research on crossmodal duration perception in the older population, multiple questions arise. Even though declines in both the visual and auditory abilities are expected, whether the dominance of the auditory system in terms of duration discrimination remains throughout the lifespan is an important issue addressed in this thesis. Another question addressed is whether auditory influences (expansion and compression effects) on visual duration perception are present in aging adults and whether there is a significant difference in the range of auditory durations that can affect visual duration perception between older and younger adults.

It has been shown that the older adult population has difficulty processing multiple senses at once. In temporal order judgment tasks, older adults have consistently been shown to have a larger temporal binding window (Bedard & Barnett-Cowan, 2016). Temporal order judgment tasks are when observers have to determine the order that an auditory stimulus and a visual stimulus occurred in. These tasks allow for the characterization of many aspects of 6 multisensory integration, such as crossmodal duration perception. The temporal binding window is the period of time which stimuli from different modalities are likely to be integrated together as one stimulus. The increased width of the temporal binding window for older adults could potentially be due to the increased processing time of both auditory and visual information (Bedard & Barnett-Cowan, 2016). Because older adults have a much wider binding window in this field of temporal research, it is expected that the window and range of auditory stimuli durations for expansion and compression effects might be wider.

This research is important because it allows for a better understanding of how information from one modality can affect another modality’s duration perception in aging adults. Age effects on duration discrimination have not been addressed before in terms of crossmodal influence. Because of the deteriorations in both the auditory and visual systems in older adult population, a general understanding on the extent to which these deteriorations affect crossmodal duration perception can lead to new avenues to explore in future studies.

Again, crossmodal duration perception is extremely important for accurately perceiving the world. Speech perception heavily relies on crossmodal duration perception, as this ability heavily relies on integrating vision and audition. Visually seeing how a person’s mouth moves greatly influences how the receiver will hear those words. Similarly, safe traveling also relies on crossmodal duration perception. Driving and walking all rely on the ability to perceive duration accurately, and if these timing processes are inhibited, then successfully bringing a vehicle to a complete stop is hindered, and walking across a busy intersection is extremely dangerous. This research will determine if crossmodal duration perception is altered in the older adult population and if they are at risk of these potentially harmful outcomes. To determine duration judgment thresholds and the extent of compression and 7 expansion effects, participants from both younger (18-35 years old) and older (65-75 years old) age groups will perform various duration judgment tasks for visual and auditory stimuli.

Here, while it is expected that the auditory system will maintain its dominance over the visual system in duration perception in older adults, auditory information should influence visual duration perception over longer duration differences between the two stimuli in older adults compared to younger adults due to a wider temporal binding window typically found in older adults.

Literature Review

Temporal perception is a broad field of study that has previously focused on simultaneity and temporal order perception and duration perception. The effect of aging on temporal perception has only been considered in simultaneity and temporal order perception, but not crossmodal duration perception. Duration perception refers to how long a stimulus is perceived to last. Depending on which modality the researchers are interested in, these stimuli could be flashes of light (visual modality), tones (auditory modality), or physical vibrations (tactile modality). Crossmodal duration perception analyzes how information from one modality (auditory) can affect the perceived duration of another (visual) and vice versa.

The gap of information that this research aims to fill is how specific crossmodal effects can affect older individuals’ duration perception.

Temporal perception research is usually focused around two modalities, audition and vision, in young, normal hearing adults. These two modalities are the most frequently studied for temporal perception and research has proven that audition has a higher temporal resolution while vision has a higher spatial resolution. This means that the auditory system is much better at processing a variety of temporal tasks and the visual system can better process spatial localization tasks. The auditory system has better temporal resolution than the visual system. For example, when measuring the just noticeable difference (JND – a factor that assesses the threshold where an individual can detect a change in two stimuli, such as weight, length, loudness, or duration), individuals can detect sound duration differences that are on average a minimum of 80 ms (Klink, Montijn, & van Wezel, 2011). When presented with a sound that is 500 ms and a sound that is 580 ms, an individual will be able to detect this 9 difference in duration. However, if the second sound was just 570 ms, the individual would no longer be able to tell the difference in duration.

While 80 ms may seem like a large threshold, the JND for visual stimuli durations is significantly longer. Individuals can typically detect differences in duration of light flashes at a minimum of 115 ms (Ortega et al., 2014). Again, individuals could detect duration differences in light flashes that are 500 ms and 615 ms, but could not detect a change in any duration difference under 115 ms. Clearly, the precision of the auditory system is greater than the visual system in detecting these duration differences. The known precision of the auditory modality has been exploited by almost all temporal perception research, and fuels the hypothesis that the auditory system is dominant over the visual in temporal processing. The dominance of the auditory system for duration thresholds is the basic principle that this thesis is based on.

Beyond temporal perception, there is an overall decline in the resolution and speed of perceptual processing as a whole due to natural aging. General tactile, auditory, and visual perception are typically affected along with the various aspects of temporal judgments that are associated with these modalities (Glorig & Roberts, 1965; Kim & Mayer, 1994;

Gescheider et al., 1996). A general hypothesis as to why this occurs in healthy aging adults could be, physiologically, reduced blood flow to peripheral tissues which leads to a decreased ability for these modalities to function at an optimal level (Lindenberger, Scherer,

& Baltes 2001). Interestingly, previous research has intensively investigated whether a link between declines in sensory processing and cognitive abilities existed, although no such link has been found (Lindenberger, Scherer, & Baltes 2001). The decline in the ability to process senses occurs independently from cognitive declines. 10

One of the first times that temporal declines in older adults were shown to have a neural basis was with Ostroff et al. (2003), who measured auditory evoked potentials (AEP – a signal similar to that of an electroencephalogram) in older adults elicited by sounds of various durations. They compared the typical waves of an AEP measurement from young adults to that of middle-aged and older adults. The researchers found that some of the wave component amplitudes did not change with increasing durations in older adults to the same extent as seen in the younger adults. This suggests that older adults have an impairment with the encoding process of different sound durations. Young adult brains experience normal fluctuations in AEP waves, but older adults do not show the same change, suggesting some form of disconnect in the pathway from the ear to the processing center. This finding is important because the fact that older adults have some form of an impairment with processing sound durations is another basis for this project.

Both auditory and visual temporal acuity suffer from normal aging. It is important to distinguish declines in these senses due to normal aging as opposed to declines due to physical impairments. Previous research has shown that while there is a significant difference in duration discrimination due to age, there is not a significant difference in duration discrimination due to unnatural hearing loss, such as injury or disease (Fitzgibbons &

Gordon-Salant, 1994). While it is possible for both modality functions to decline to some extent with age, the degree to which one modality is affected is independent of the other modality (Humes et al., 2009). In other words, magnitudes of sensory decline across modalities cannot be predicted based on the magnitude of one affected sense.

Another useful way to determine temporal resolution of both modalities is a gap detection test. Gap detection is when a participant has to determine whether a physical 11 temporal gap exists between two sounds or two light flashes, or whether no gap exists at all.

These gap detection tasks can help predict how an individual will perform on other duration tasks. In gap detection tasks for visual temporal thresholds, older adults have a significantly longer gap detection threshold than younger adults (Strouse et al., 1998; Humes et al., 2009).

Again, this indicates that older individuals have multiple types of temporal perception impairments.

Duration judgment task results for auditory and visual modalities found that older adults will estimate the length of either stimulus to be longer than it physically is (Block,

Zakay, & Hancock, 1998). These duration discrimination judgment tasks require listeners to distinguish incremental changes in the length of a reference stimulus. Previous research has hypothesized that older adults have a slowed, impaired processing of sound durations, proven later by Ostroff et al. (2003), especially when the sounds are complex in cases such as speech

(Phillips et al., 1994). The hypothesis that speech perception is affected by increasing age is supported by other gap detection tasks. Schneider and Hamstra (1999) found that older adults have more difficulty detecting an auditory gap with short reference durations than when longer reference durations were used. These shorter reference sounds were related to characteristics that are similar to speech sounds. Since these characteristics are similar, the researchers hypothesized that older adults have an impairment in perceiving speech. Due to speech conversation being a crossmodal event, where those involved both hear each other speak and see mouths move, reliable crossmodal duration perception is necessary for accurate speech processing. Duration judgments as a whole are affected by aging; which is the reason that this thesis addresses age effects on duration judgments in crossmodal perception. 12

As previously discussed, the auditory and visual modalities are the most frequently studied in terms of temporal perception research. This is because these two have the highest temporal resolution over other modalities. However, previous research has shown that the auditory modality has a better temporal resolution over the visual system. Because of these differences in resolution, the brain frequently uses auditory information whenever it can to make judgements of visual duration perception. While crossmodal perception is necessary for making normal everyday judgments, such as crossing a street, driving, and even speech comprehension, the integration of these modalities can often lead to internal conflicts that cause altered perceptions of reality. Research comparing audition and vision found that when participants are presented with a brief auditory stimulus of 1,000 ms and then a brief visual stimulus of the same duration, the auditory stimulus was perceived as significantly longer than that visual stimulus (Walker & Scott, 1981). The researchers then analyzed how perception would be affected if the two stimuli, auditory and visual, were presented simultaneously. They found that the perceived duration of a paired stimulus (both a light and a beep presented together) was closer to the physical duration of the beep alone rather than the physical duration of the light alone. This finding was one of the first times that the auditory modality was shown not only to be dominant in temporal processing, but also that duration perceptions can be influenced by information from another modality. Prior to this research, it was known that the visual system was dominant to spatial perception. While not extensively studied yet, the visual modality was assumed to be dominant in both spatial and temporal processing, which it clearly is not.

At this point, while it was known that auditory information could influence duration perception of visual stimuli, it was unknown whether visual information had any effect on 13 auditory duration perception. Proving the latter did not occur would verify that the crossmodal influence was asymmetric, meaning it only occurred in one direction. This would show that audition was truly dominant over vision for duration processing. This is exactly what Chen and Yeh (2009) set out to prove. While considering two separate experiments that presented contrasting hypotheses, one claiming auditory dominance (Walker & Scott, 1981) and one claiming visual dominance (van Wassenhove et al., 2008), Chen and Yeh (2009) wanted to verify that audition was in fact dominant using van Wassenhove’s methods. The researchers found that when participants were rating the duration of visual targets, the presence of an auditory stimulus greatly influenced their ratings as opposed to when an auditory stimulus was absent. They also found that when participants were judging the durations of auditory stimuli, both the presence and absence of a visual stimulus had no effect on the participants’ ratings. These results supported the audition dominant hypothesis; that sounds can influence the subjective judgement of visual duration perception, but not the other way around.

With this information, determining to what extent auditory information can influence visual duration perception would be important in expanding the knowledge of this topic.

Romei et al. (2011) extensively tested different aspects of the crossmodal perception to determine the parameters stimuli must follow in order for the influence effects to occur.

These aspects include how close the two different stimuli could be presented together, and the lengths that the non-target auditory stimuli could last before the effect of altered visual duration perception was no longer seen. Their research found, like previous results, that duration discrimination of visual stimuli can be modulated by co-occurring auditory information. However, Romei et al. (2011) found this influence only happened when the co- 14 occurring stimuli were presented with their starting points aligned synchronously (front alignment), as opposed to one stimulus being delayed by 500 ms. Synchronicity was expanded upon in later research that found auditory onsets of varying durations cause intervals to be perceived as longer than intervals with auditory offsets (Mayer et al., 2014).

Auditory onset means that the auditory stimuli begins before the paired visual stimuli, while auditory offset refers to auditory stimuli that ends after the visual stimuli, both under 1000 ms delays. Overall, significant influence effects were seen when the paired stimuli were front aligned. In Klink et al. (2011), the stimuli they presented to participants were center aligned, meaning the midpoints of a visual and an auditory stimulus were co-occurring. These researchers also found significant effects with this alignment, so comparing the influence strength of front versus center aligned stimuli would be interesting.

Romei et al. (2011) also found that the duration of the auditory stimulus had to be relatively similar to the visual stimulus that the auditory stimulus was trying to influence.

When the researchers made the sound stimulus three times longer than the physical duration of the visual stimulus, the perceived duration of the visual was no longer influenced. Specific durations of how long or short the auditory stimuli needed to be before visual perception was no longer influenced was also studied with regard to expansion and compression effects

(Klink, Montijn, & van Wezel, 2011). An expansion effect occurs when an auditory stimulus is longer than a co-occurring visual stimulus and the viewer perceives the visual stimulus to be longer than it physically is. A compression effect is when an auditory stimulus is shorter than a co-occurring visual stimulus and the viewer perceives the visual stimulus to be shorter than it physically is. 15

These effects are observed when the duration difference between visual and auditory stimuli is 300 ms or less (Klink, Montijn, & van Wezel, 2011). Duration differences greater than these resulted in no significant perceived expansions or compressions of the visual stimuli. The disappearance of the expansion effect could potentially be explained by adaptation experiments (Heron et al., 2012). Here, it was shown that adapting to really long auditory durations could actually cause a compression of perceived visual duration.

Adaptation is the perceptual effect that occurs when presented with a consistent stimulus with consistent characteristics. For example, when one rests their hand on a table, they immediately sense the feeling of the table on the hand. But if the hand is left there for a while, the individual tends to not pay attention to this feeling anymore, which is an altered perception of reality. The adaptation to auditory or visual events of consistent durations induces alterations in perceived duration. This effect is restricted however; durations of stimuli that are sufficiently different fail to influence the perception of those stimuli (Heron et al., 2012). Exposure to a very long stimulus consistently could potentially cause an inverted effect when a different stimulus is presented to the observer.

While this current thesis does not focus on adaptation, a similar pathway may be involved, as when the auditory stimulus has too large of a duration difference than the co- occurring visual stimulus, the visual stimulus may be perceived to be shorter than it physically is rather than longer (Heron et al., 2013). The temporal binding window is the time period that two stimuli from different modalities must fall in order to be perceptually linked together in time. Previous research has shown that older adults typically have a much wider binding window than younger adults (Bedard & Barnett-Cowan, 2016). Older adults will perceive two stimuli that are not simultaneous as simultaneous over greater duration 16 differences than younger adults. This finding is the basis for this thesis’ prediction that the window for compression and expansion effects to occur will be wider for older adults than younger adults.

Unisensory duration perception has extensively been studied in both younger and older adult populations. Yet crossmodal duration perception has not been intensively investigated in older adults, a population that has significant declines in the processing capabilities of the auditory and visual system. Other factors of crossmodal perception that have not been addressed include the alignment of paired stimuli, and whether auditory dominance remains throughout a lifetime or changes, or simply vanishes. This thesis aims to fill some of these gaps of knowledge about crossmodal duration perception in an aging population. Hopefully, knowledge gained from these results will fuel the advancement of research on perceptual changes as a function of age, and provide insight into the mechanisms of how sensory declines can affect crossmodal duration perception. Natural declines due to age should affect crossmodal duration perception by expanding the range of auditory durations that can influence the perceived duration of visual stimuli.

Methodology

Overview In order to assess how crossmodal influence affects older individuals’ duration perception, three main experiments were performed. The first experiment measures the duration judgement thresholds for visual, auditory, and audiovisual stimuli. This task assesses whether older individuals have a higher auditory acuity for short durations, like has been seen in young adults, or if there is an effect of age on the sensitivity of either modality in duration perception. Using the results from this task, the next goal was to determine whether the dominance of the auditory modality in influencing visual duration perception is retained during aging. Finally, the extent to which expansion and compression effects are seen in older adults was assessed.

Participants The same participants were used for all three experiments. Fourteen young participants (18-23 years old, mean = 20.9 ± 0.7 years old, 4 males and 10 females) were all recruited from the University of Nevada, Reno. Ten older participants (66-73 years old, mean

= 68.7 ± 1.5 years old, 2 males and 8 females) were recruited from the university and the surrounding community. All the participants were screened for hearing (pure tone threshold

< 40 dB for 1000-2000 Hz) and vision (best-corrected binocular visual acuity > 20/25). All participants were naïve to the purpose of the experiment and were tested individually in a quiet, dark room. All participants gave informed consent and received $20 per hour for their time (approximately 2 hours for younger participants and 3 hours for older participants)

Apparatus and Stimuli Visual and auditory stimuli were generated using MATLAB and the psychophysics toolbox. Visual stimuli were 3.5 degree white circles presented at the center of a monitor against a gray background. Auditory stimuli were beeps presented at 75 dB via a speaker at a frequency of 1000 Hz. Visual and auditory stimuli were delivered via Display++ system and an AudioFile stimulus processor, respectively (Cambridge Research Systems). The use of these two devices allowed for precise control of stimulus timing.

Experiment 1 – Visual, Auditory, & Auditory-Visual JND Thresholds Duration thresholds for auditory, visual, and audiovisual stimuli were determined for both young and older participants. JND thresholds determined in this experiment were used to define the durations in experiment 2. Here, levels of auditory and visual acuity from older adults were compared to those of younger adults. In order to find the individual thresholds, subjects were presented with a standard stimulus of 500 ms, a brief pause that randomly varied between 1450 and 1550 ms, and then a test stimulus of varying duration. These test stimuli varied from 5 ms to 1000 ms in 5 ms increments. They were asked to judge whether they perceived the test stimulus to be shorter or longer in duration than the standard 500 ms stimulus. Depending on their response, a staircase procedure following the QUEST algorithm determined the duration of the test stimuli for all subsequent phases (Watson & Pelli, 1983).

For each condition (auditory, visual, and audiovisual), a total of 3 blocks of 40 trials each were performed for a total of 120 trials for each subject per modality. These 120 trials determined the threshold values in each condition. Thresholds were calculated converging on

82% correct, which determines the minimal duration difference a participant required to reliably detect a difference 82% of the time. Thresholds were determined for auditory, visual, 19 and audiovisual duration perception. Note that for the audiovisual duration threshold task, the standard stimulus was in the visual modality and the test stimulus was in the auditory modality. Participants were always presented with a flash that lasted 500 ms, and then were presented with beeps of varying durations. The setup of experiment 1 can be seen in Figure 1. 20

1450-1550 ms

Figure 1. Visual representation of experiment 1 design

Experiment 2 – Auditory Influence on Visual Duration Perception Next, the influence of non-target auditory information on visual duration perception was examined. Alternatively, whether non-target visual information can influence the perceived duration of auditory stimuli was also tested. Prior to the presentation, observers were notified whether their target stimulus was visual or auditory. The objective of notifying participants of the target stimulus was to draw attention to the modality being tested at that instance. Participants were instructed to focus their attention only on the target stimuli.

On each trial, two pairs of stimuli were presented. Within each pair, the target stimuli always co-occurred with the non-target stimuli of the other modality. The non-target stimuli’s purpose was to influence the perception of the target stimuli’s duration. In order to individualize this task based on the participant’s threshold, the target stimuli always had a duration of 500 ms +/- individual JND/2. The individualized JND allows to test whether participants perform at their 82% threshold level, or whether their duration perception of the target stimulus is influenced by the non-target stimulus.

In half of the trials, the non-target and target stimuli had the same duration (NT Same condition). The longer (500 ms + JND/2) and the shorter (500 ms – JND/2) target stimuli were each paired with non-target stimuli that had a duration of 500 ms. The order in which the longer and shorter target stimulus was presented was randomized.

In the other half of the trials, the non-target stimulus was either shorter or longer than its paired target stimulus (NT different condition). In one pair, the non-target stimulus had a duration of 400 ms and in the other pair, the non-target stimulus had a duration of 600 ms. In this condition, the 400 ms non-target stimulus was always paired with the longer target stimuli (500 ms + JND/2), and the 600 ms non-target stimuli was always paired with the 22 shorter target stimuli (500 ms – JND/2). After each trial, participants were asked to judge which of the two target stimuli was longer in duration. For each target modality, 2 blocks of

40 trials were conducted, for a total of 80 trials each. The experimental setup for this experiment can be seen in Figure 2.

1450-1550 ms 1450-1550 ms

Figure 2. Visual representation of experiment 2 design

Experiment 3 – Expansion and Compression Effects In the final experiment, the range of expansion and compression effects in older adults were measured. Not all of the participants from the previous two experiment participated in the final experiment. Thirteen young participants (18-23 ± 1.4 years old, mean

= 20.8 years old, 4 males and 9 females) and eight older adults participants (66-73 ± 2.2 years old, mean = 68.9 years old, 2 males and 6 females) completed the final experiment. The observers were asked to focus only on the visual stimuli. Similar to Experiment 2, two paired stimuli were presented. In the standard pair, both the visual and auditory stimuli had a duration of 500 ms. In the test pair, the visual stimulus was 500 ms while the auditory stimulus randomly varied between 100 and 900 ms at 50 ms increments.

Alignment of auditory stimuli to the paired visual stimulus was also assessed when the auditory stimulus was longer than the visual stimulus. Due to the fact that both front and center aligned paired stimuli have significant influence effects, these two conditions were tested to compare the strength of the influences from the different alignments. Auditory stimuli were either center aligned to their paired visual stimulus (meaning the midpoints of each duration were linked together), or front aligned to their paired visual stimulus (meaning that both stimuli started at the exact same time, regardless of the total durations).

Unfortunately, due to a technical error, for auditory test durations that were < 500 ms, the stimuli were only center aligned.

The participants were asked to determine whether the second visual stimulus they observed was perceived to be longer or shorter in duration than the first visual stimulus, even though they were physically the same duration (unknown to the participants). The order of 25 the standard and the test stimuli was randomized. This experiment had 3 blocks, with 85 trials in each block for a total of 255 trials. The proportion of responses determining the test visual stimulus as longer than the standard visual stimulus was calculated at each duration difference between the auditory and visual stimulus in the test pair. This allowed for an estimation of the effect of auditory stimuli on perceived duration of visual stimuli as a function of the duration difference. The experimental setup can be seen in Figure 3.

1450-1550 ms

550-900 ms

Figure 3. Visual representation of experiment 3 design

Results

Experiment 1 – Visual, Auditory, & Auditory-Visual JND Thresholds

Individual just-noticeable differences were measured for all three conditions for the two age groups. Figure 4 displays the thresholds converging on 82% correct for the different modalities. A mixed ANOVA confirmed there was not a significant effect of age on the ability to temporally discriminate the duration of visual, auditory, or AV stimuli, F(1,22) =

0.383, p = 0.542. There was a significant difference in the thresholds of the modalities across the age groups, F(2, 44) = 14.108, p < 0.001. No significant interaction was found between the two factors (age vs. modality), F(2,44) = 0.242, p = 0.786. The average thresholds of visual stimuli at a base of 500 ms for the young (n=14) and older adults (n=10) were 113.9 ms (SE = ± 10.2 ms) and 130.1 ms (SE = ± 22.8 ms), respectively. The average thresholds of auditory stimuli again for the young and older adults were 60.6 ms (SE = ± 5.2 ms) and 62.6 ms (SE = ± 8.0 ms), respectively. Finally, when comparing auditory stimuli to a 500 ms visual stimulus, the average thresholds for the young and older adults were 92.6 ms (SE = ±

13.7 ms) and 97.8 ms (SE = ±15.3 ms). These results demonstrate that age is not a significant contributor to the JND thresholds for any temporal detecting modality.

Games-Howell post-hoc tests confirmed the average means for auditory thresholds were significantly lower than both visual thresholds and AV thresholds. The means of auditory and visual thresholds were significantly different as expected, t(23) = 6.57, p<0.001.

The means of auditory and AV thresholds were also significantly different, t(23) = 3.59, p<0.01. Visual thresholds approached, but were not significantly different than AV thresholds, t(23) = 1.76, p = 0.07485. Here, it is clear that both age groups are much better 28

Figure 4. Mean thresholds at 82% for the visual, auditory, and audiovisual modalities. Using the QUEST staircase procedure, the JNDs across modalities were measured across age groups. The auditory modality proved to have a lower threshold than both the visual and the audiovisual modalities. No age differences were found.

able to distinguish durations of auditory stimuli than visual stimuli, as expected due to the dominance of the auditory system for temporal events.

Experiment 2 - Auditory Influence on Visual Duration Perception

Individual thresholds were used as parameters for each participant to determine whether auditory information could influence the duration perception of visual stimuli, or whether visual information could influence the duration perception of auditory stimuli.

Figure 5 displays the percent correctly identified longer target stimuli (both auditory (A) and 29

Figure 5. Modality influence on duration perception. Both younger and older adults were tested to determine whether visual information can influence auditory duration perception (A), and whether auditory information can influence a visual target’s duration perception (B). Age did not have an effect on temporal dominance; both age groups’ visual duration perception was influenced by auditory information. 30 visual (B)) when the non-targets had the same duration of 500 ms and when the non-targets had different durations of 400 ms and 600 ms. The factors analyzed here were age (between), target modality (within), and the duration of the non-target stimuli (within). A mixed

ANOVA showed that the effect of age on all non-target influences of duration perception approached but failed to reach significance, F(1,22) = 2.499, p = 0.128. The target modality did have a significant effect on the percent correctly identified longer targets, F(1,66) =

323.648, p < 0.001. Whether the non-target stimuli were the same or different durations as the target also proved to be significant in affecting the participants’ ability to correctly identify the longer target, F(1,66) = 100.516, p < 0.001. The interaction between age and target modality was insignificant, F(1,66) = 1.436, p = 0.235. No interaction was found between age and duration of non-target stimuli, as expected, F(1,66) = 0.012, p = 0.913.

Finally, a significant interaction was found between target modality and duration of non- target stimuli, F(1,66) = 79.483, p < 0.001. There was no interaction between all three factors, as expected, F(1,66) = 0.084, p = 0.773.

To analyze the simple effects of the significant interaction, two one way ANOVAS were performed to examine the effect of non-target duration separately for each target modality. Non-target duration had no effect on participant’s perception when the target modality was auditory, suggesting no visual influence, F(1,46) = 0.5795, p = 0.4504. Non- target duration did have an effect on perception when the target modality was visual, suggesting auditory information can influence visual duration perception, F(1,46) = 140.82, p

< 0.001.

When testing visual influence on auditory target duration perception, the mean correctly identified longer targets for the young and older adults when the non-target 31 durations were both 500 ms were 79.0% (SE = ± 2.7%) and 72.3% (SE = ± 3.3%), respectively. When the non-target durations were different, young and older adults performed at 76.9% (SE = ± 2.8%) and 69.5% (SE = ± 3.7%) correct, respectively. Each of these values were not significantly different than threshold at 82% at a corrected 훼 for 8 tests.

Significance would need to meet a p-value less than 0.00625. For the young and NT Same condition, t(13) = -1.1229, p = 0.2818; older adults and NT Same, t(9) = -2.9748, p =

0.01558; young and NT Different, t(13) = -1.8253, p = 0.09101; and older adults and NT

Different, t(9) = -3.4221, p = 0.007603. Both older adult conditions for the auditory target modality approached but failed to reach significance. These results conclude that visual information is unable to significantly influence auditory duration perception.

The mean correctly identified longer targets when testing auditory influence on visual target duration perception for young and older adults when non-targets had the same duration were 57.7% (SE = ± 2.7%) and 55.0% (SE = ± 2.7%) correct, respectively. Participants performance when the non-target durations were different was 16.0% (SE = ± 3.1%) for young and 15.1% (SE = ± 5.5%) for older adults. These values were all determined to be significantly different than 82% threshold level. For young and non-target same, t(13) = -

8.8919, p < 0.001; older adults and non-target same, t(9) = -9.9015, p < 0.001; young and non-target different, t(13) = -21.0467, p < 0.001; and older adults and non-target different, t(9) = -12.1965, p < 0.001. These results suggest that the auditory modality is still dominant for temporal perception throughout the aging process.

Experiment 3 - Expansion and Compression Effects

The extent of expansion and compression effects seen when a standard visual stimulus of 500 ms is paired with a longer and shorter auditory stimulus, respectively, was measured in both age groups. When the auditory stimulus was shorter than the standard visual stimulus, the stimuli were always aligned by their midpoints. A mixed ANOVA contrasting the between-subjects factor of age and within subject factor of auditory duration did not reveal a significant effect of age, F(1,185) = 0.822, p = 0.366. However, there was a significant effect of auditory duration, F(1,185) = 121.58, p < 0.001. There was no significant interaction, F(1,185) = 1.632, p = 0.203.

When the auditory stimulus was longer than the standard visual stimulus, the stimuli were front aligned for half of the trials and center aligned for the other half. The factors considered for the results of this experiment are age, alignment of test stimuli, and duration of the auditory test stimuli. A mixed ANOVA confirmed that only the between subjects factor, age, was not a significant factor that affects the perceptual compression and expansion of visual stimuli, F(1,328) = 0.286, p = 0.593. A surprising finding was that alignment of auditory stimuli to the test visual stimulus had a very significant effect on participants’ perception, F(1,328) = 151.102, p < 0.001. As expected, the duration of the auditory stimulus also had a significant effect, F(1,328) = 18.880, p < 0.001. These results are outlined in

Figure 6.

There was also a significant interaction between alignment and the duration of auditory stimuli, but not age, F(1,328) = 62.584, p < 0.001. In order to characterize the interaction, two separate one way ANOVAs were ran to determine if the alignment was dependent on the duration of the auditory stimulus. Front and centered alignment showed no 33

Figure 6. Expansion and compression effects of young and older adults. Comparing the effects of age and alignment for visual expansion and compression, only alignment has a significant effect. There was no difference between any duration difference between young and older adults.

effect on the responses when the auditory test stimuli were shorter than the visual test stimulus, F(1,334) = 0.2064, p = 0.6499. On the other hand, the alignment did have a significant effect on responses when the auditory test stimuli were longer than the visual test stimuli, F(1,334) = 122.64, p < 0.001.

Finally, in order to determine if the longer and shorter durations revealed a significant expansion and compression effect, multiple linear regression analysis was used to compare the effects of auditory duration, alignment, and age. The predictor, auditory duration, and the dependent variable, percentage of ‘test longer’ responses, were standardized by mean- centering prior to regression analysis. Because we only included alignment as a factor when auditory durations were longer than the standard visual stimulus, we created 2 separate models. The first model included auditory duration lengths between 100 and 500 ms and 34 included age as a factor (Figure 7A). The multiple linear regression generated an adjusted r2 of 0.392, F(3, 185) = 41.34, p < 0.0001. While age was not a significant predictor, β = 0.106, t(185) = 0.907, p = 0.366, duration length was significant, β = 0.720, t(185) = 7.81, p <

0.0001, indicating a significant compression effect occurred in both age groups.

The second model included auditory duration lengths between 550 and 900 ms and included both age and alignment as predictors (Figure 7B). The multiple linear regression generated an adjusted r2 of 0.405, F(7, 328) = 33.52, p < 0.0001. Again, age was not a significant predictor of expansion effects, β = -0.079, t(328) = -0.627, p = 0.531. However, both auditory duration length (β = -.468, t(328) = -4.397, p < 0.0001) and alignment were,

β = 0.933, t(328) = 6.621, p < 0.0001. These main effects were qualified by a significant interaction between alignment and auditory duration, β = .631, t(328) = 4.188, p < 0.0001. As can be viewed in Figure 7, when a longer auditory stimulus was front aligned with the visual test stimulus, an expansion effect occurred. However, when a longer auditory signal was center-aligned with the visual test stimulus, a compression effect was observed.

A B

Figure 7. Linear regression analysis for effect of alignment and age. The compression/expansion effects were analyzed separately depending on whether the auditory stimulus was either A) between 100- 500 ms, or B) between 550-900 ms. Age was not a significant contributor to both perceived compression and expansion. However, the alignment of stimuli was, as front aligned produced expansion effects and center aligned produced compression effects (B).

Discussion The main hypothesis of this project was that older adults will experience compression and expansion of visual duration perception over a wider range of auditory durations because they have a wider temporal binding window as compared to younger, normal hearing adults.

It was also expected that older individuals would have higher duration thresholds for the auditory and visual modalities. Surprisingly, across all three experiments, age had no significant effect on unimodal or crossmodal duration perception. These results failed to reject the null hypothesis that age did not play a role in crossmodal duration perception.

Experiment 1 - Visual, Auditory, & Auditory-Visual JND Thresholds

In experiment 1, the JND thresholds for auditory, visual, and audiovisual duration were measured. As expected, the auditory modality had a significantly smaller threshold than the visual threshold and the audiovisual threshold for both age groups (Fig. 4). This reflects that the auditory modality has a higher resolution for discriminating durations of sounds, and overall duration perception in general. These results were expected; however, the fact that age played no role in the threshold values for the tested modalities is surprising. Previous research has found significant differences in duration discrimination due to age (Fitzgibbons

& Gordon-Salant, 1994). The obtained results were unexpected; thresholds for younger and older adults were almost identical. Age also failed to cause an interaction between that factor and modality. If age did interact with modality for threshold determination, this would reveal that the visual system is dominant in duration discrimination as opposed to auditory dominant in older adults. This result was expected as the rest of the project was based on the 37 assumption that the auditory system is better suited to discriminate duration differences than the visual system across age groups.

Experiment 2 - Auditory Influence on Visual Duration Perception

In experiment 2, crossmodal influence was measured for both age groups. If visual information does not influence auditory duration perception, participants should be able to accurately determine which auditory stimuli was longer at threshold level (82%). As seen in

Figure 5, participants do perform at threshold level when the target modality was audition.

When the non-target flashes were both 500 ms and when the flashes were 400 ms and 600 ms, the participants were able to accurately determine which auditory stimulus lasted longer.

These results did not significantly deviate from threshold level, which means that non-target

(distractor) visual information did not significantly influence the perceived duration of auditory information. This finding extended to both the younger and older participants as expected. Older participants were still expected to perform above chance level (50%) as this would show that the visual modality does not have the capability to influence their perception of auditory modality.

The influence that auditory information has on visual duration perception was also tested. If auditory information is able to influence visual duration perception, then participants should perform much lower than threshold level. This is due to the longer visual target being paired with the shorter 400 ms non-target auditory stimulus, and the shorter visual target being paired with the longer 600 ms non-target auditory stimulus. Participants would incorrectly choose the target stimulus with the longer duration because they experience a perceptual expansion of the short target and a perceptual compression of the 38 longer target. This hypothetical result is exactly what was observed in the current project.

When analyzing results of the visual target and non-targets with different durations, the participants’ responses are significantly different from threshold level. This confirms that auditory information is able to influence visual duration perception. This also confirms that crossmodal influence on duration is a one-way effect: auditory information influence visual duration perception and not the other way around. These results prove not only that the auditory modality has a higher temporal resolution, it is also the dominant modality in crossmodal duration perception. Results for visual target and when the non-target auditory durations were both 500 ms were at roughly chance level. When participants view this condition, the two visual target stimuli, while physically different, appear to also have the same duration of 500 ms. Therefore, their response would be up to chance for which light stimulus they appeared to have a longer duration. When auditory is the target and the non- target durations are the same, responses are not up to chance because visual information does not influence auditory duration perception.

There was no effect of age on any of the conditions of this particular experiment as expected, which shows that the auditory modality can influence visual duration perception for both age groups. Any effects of age would mean that the auditory modality is not dominant to the same extent (or at all) for older adults like it is for the younger population.

Age did not have a significant effect on the percentage of correctly identified longer targets for any condition, proving that the auditory modality is dominant in influencing the duration perception of visual stimuli across age groups.

Experiment 3 - Expansion and Compression Effects

The purpose of experiment three was to assess the expansion and compression effects in the younger and older adults that occur when a standard visual stimulus of 500 ms is paired with longer and shorter auditory stimuli, respectively. There were 17 different auditory duration points that participants had to compare to a standard duration of 500 ms

(100 - 900 ms in 50 ms increments). In order for a significant compression effect to be seen, the visual stimulus paired with any auditory duration below 500 ms should very rarely be perceived as longer. This would mean that a compression effect was observed by the participant and they rarely perceived the visual stimulus paired with the test auditory stimulus to be longer than the visual stimulus paired with the standard auditory stimulus.

Alternatively, for a significant expansion effect to occur, the visual stimuli that is paired with any auditory duration above 500 ms should almost always be rated as the longer of the two stimuli in the trial.

An interesting finding was that perhaps the strongest effect for the third experiment was due to alignment of auditory stimuli to the paired visual stimuli. For both age groups, when the auditory stimuli were front aligned and > 500 ms, participants showed a preference to answer that visual stimuli were longer. However, when the auditory was center aligned and > 500 ms, participants showed a preference to answer that visual stimuli were shorter.

Both age groups perceived significant compression effects when the auditory stimuli were <

500 ms and center aligned. This means that when the auditory stimuli are center aligned and

> 500 ms, a compression effect occurs instead of an expansion. These results are contrary to the previous experiment that this thesis was based on. Klink et al. (2011) found significant expansion effects when the auditory stimuli was center aligned. The mechanism of this 40 surprising discovery is unknown. There were minor differences between the current project and Klink et al. (2011). Their test auditory stimuli had a much lower sound frequency than this experiment. Their test stimuli were presented at 200 Hz, while our auditory stimuli were presented at 1000 Hz. The other difference between the two projects was that Klink et al.

(2011) only had a paired visual/auditory stimulus for their test presentation; their standard stimulus was just a 500 ms flash without the paired beep. Whether these differences could be the potential reason for the discrepancies between the two projects will be tested in future studies.

To determine whether the initial main hypothesis of this project was supported, the idea of age as a responsible factor must be accounted for. Similar to the rest of the results of this project, age surprisingly had no effect on the perception of visually compressed or expanded stimuli. No significant difference was found due to age at any of the 17 durations for both alignment conditions. This finding suggests, that normal hearing young and older adults experience crossmodal effects on duration very similarly.

Conclusions

To conclude, age differences between normal hearing adults does not have an effect on any factor of crossmodal duration perception. The lack of age differences will have to be extensively tested in the future to determine whether it is accurate or whether there was a flaw in this project. There were a few limitations in my project that may have increased the variability in the data obtained. In order to schedule enough participants, some tests were conducted early in the morning (as early as 7:30am) and some were conducted later at night

(starting as late as 8:00pm) and the entire experiment often lasted up to three hours for elderly individuals. It is possible that those individuals that participated either early in the morning or late at night were susceptible to the auditory influences to a different degree than those participating in the middle of the day. Whether time of day and wakefulness is able to change a person’s crossmodal perception is unknown and should be controlled for during future applications of this research.

Another limitation was the low sample size for each age group. Again, as it is difficult to juggle schedules of everyone involved for a three-hour experiment, only 24 total people were recruited for this study. As seen by the results of experiment three, the standard error is fairly large for older adults’ responses. Only eight older individuals were tested in experiment three, compared to thirteen younger individuals. If more older individuals could have participated, it is likely that the standard error would have decreased significantly.

Finally, there was an error in the coded program for the third experiment that only allowed front aligned paired stimuli to be presented when the auditory stimulus was greater than 500 ms. The way the code was written disregarded the ability for two different alignment conditions to occur for auditory stimuli shorter than 500 ms. This error caused a 42 lack of data to be obtained for those shorter auditory durations. Future studies will need to fully examine the effect that different alignment of paired stimuli have on the perceived compression and expansion of visual stimuli by including frontal alignment of paired stimuli for both longer and shorter auditory durations.

The goal of this study was to illuminate perceptual declines due to aging. Countless real world experiences utilize crossmodal duration perception to garner an accurate representation of life: from speech perception to motion perception. While it has been proven that some older individuals have declines in their ability to effectively perceive speech and motion, this project is not currently able to attribute those declines to crossmodal duration perception and the extent to which these perceptual influences were studied. However, this project did find the importance of stimuli alignment for auditory information to influence visual duration perception, a previously unknown factor for crossmodal duration perception.

While no effects due to age were observed, this project did define the auditory and visual duration thresholds of older adults, and also showed that audition was the dominant modality in crossmodal perception that can influence visual duration perception. This project also found, contrary to initial expectations, that both young and older adults view compression and expansion effects similarly across the same duration differences. A surprising finding was that alignment had a significant effect on auditory durations greater than 500 ms. When auditory stimuli were front aligned, participants experienced expansions as expected. But when auditory stimuli are center aligned to the visual stimulus, a very strong compression effect is created.

Prior to this research, it was unknown based on previous studies that front and center alignment could have different influence effects when auditory stimuli are greater than 43 standard durations. Future research must combine these aligned stimuli in a single experiment to determine whether the results obtained in this project can be replicated.

Overall, it can be concluded that all adults with normal hearing should be considered for crossmodal duration perception research, no matter the age. While there are not implications for age influencing declines of crossmodal duration perception will seek to understand the mechanisms underlying crossmodal duration perception and why alignment of visual and auditory stimuli exerts such a strong and different influence effect.

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