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 by Dustin W. Dutcher Dr. Fang Jiang, Thesis Advisor May, 2018 i 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. ii 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. iii 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 iv 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 1 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