An Adaptation-Induced Repulsion Illusion in Tactile Spatial Perception

INVESTIGATION OF AN ADAPTATION-INDUCED TACTILE SPATIAL ILLUSION INVESTIGATION OF AN ADAPTATION-INDUCED TACTILE SPATIAL ILLUSION: PSYCHOPHYSICS AND BAYESIAN MODELING By LUXI LI, Hon. B.Sc. A Thesis Submitted to the School of Graduate Studies in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy McMaster University © Copyright by Luxi Li July 2017 Ph.D. Thesis – Li, L. McMaster University - Psychology McMaster University DOCTOR OF PHILOSOPHY (2017) Hamilton, Ontario (Psychology) TITLE: Investigation of an adaptation-induced tactile spatial illusion: psychophysics and Bayesian modeling AUTHOR: Luxi Li, Hon. B.Sc. (McMaster University) SUPERVISOR: Dr. Daniel Goldreich NUMBER OF PAGES: xiv, 128 ii Ph.D. Thesis – Li, L. McMaster University - Psychology Lay Abstract Sensory adaptation can shape how we perceive the world. In this thesis, we showed that the perception of space in touch is pliable and subject to the influence of adaptation. Psychophysical testing in human participants showed that vibratory adaptation induced an illusion that expanded the perceived distance between stimuli on the skin. This illusion provides clues into how information about space in touch is normally processed and interpreted by the brain. In addition, we developed a computational model that used a powerful statistical framework – Bayesian inference – to investigate touch on a theoretical basis. To the best of our knowledge, the present thesis provides the first combined psychophysical and computational study on the effects of adaptation on tactile spatial perception. Our findings suggest that touch shares some common information processing principles with vision and hearing, and adaptation plays a functionally similar role in mediating this process across the senses. iii Ph.D. Thesis – Li, L. McMaster University - Psychology Abstract Sensory adaptation is an important aspect of perception. A seemingly non-beneficial consequence of adaptation is that it produces perceptual illusions. For instance, following focal adaptation, the perceived separation between stimuli straddling the adapted attribute or region is often exaggerated. This type of illusion, known as perceptual repulsion, is both a consequence of and a clue to the brain’s coding strategies and how they are influenced by recent sensory events. Adaptation-induced perceptual repulsion has been well documented in vision (e.g. the tilt aftereffect) and to a lesser extent in audition, but rarely studied in touch. The present thesis investigated the effects of adaptation on tactile spatial perception using a combination of human psychophysics and computational modeling. In a two-interval forced choice task, participants compared the perceived separation between two point-stimuli applied on the forearms successively. The point of subjective equality was extracted as a measure of perceived two-point distance. We showed that tactile spatial perception is subject to an adaptation-induced repulsion illusion: vibrotactile adaptation focally reduced tactile sensitivity and significantly increased the perceived distance between points straddling the adapted skin site (Chapter 2). This repulsion illusion, however, was not observed when the intervening skin was desensitized with topical anesthesia instead of vibrotactile adaptation, suggesting that peripheral desensitization alone is insufficient to induce the illusion (Chapter 3). With Bayesian perceptual modeling, we showed that the illusion was consistent with the hypothesis that the brain decodes tactile spatial input without awareness of the adaptation state in the nervous system (Chapter 4). Together, the empirical and theoretical work furthers the understanding of dynamic tactile spatial coding as the somatosensory system adapts to the sensory environment. Its main findings are consistent with the adaptation- induced repulsion illusions reported in vision and audition, suggesting that perception in different sensory modalities shares common processing features and computational principles. iv Ph.D. Thesis – Li, L. McMaster University - Psychology Preface This thesis is composed of five chapters. Chapter 1 overviews the background literature in tactile perception, sensory adaptation, and perceptual illusions, and introduces the reader to Bayesian ideal observer analysis. Chapters 2 and 3 are empirical studies using psychophysical experimentation in human participants. Chapter 2 is published in the open-access journal Frontiers in Human Neuroscience 1, and is permitted for inclusion in the thesis under the terms of the Creative Commons Attribution License2. Chapter 4 is a computational modeling study exploring the empirical results described in Chapters 2 and 3. Chapter 5 discusses the findings and implications of these studies. The research detailed in this thesis was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant awarded to Dr. Daniel Goldreich. It was also supported through an annual graduate stipend from 2011 to 2016 by McMaster University. 1 Li, L., Chan, A., Iqbal, S. M., & Goldreich, D. (2007). An adaptation-induced repulsion illusion in tactile spatial perception. Front. Hum. Neurosci. 11: 331. doi: http://10.3389/fnhum.2017.00331 2 https://creativecommons.org/licenses/by/4.0/ v Ph.D. Thesis – Li, L. McMaster University - Psychology Declaration of Academic Achievement Chapter 2 I was involved in all aspects of this empirical research: experimental design, programming, data collection, statistical analysis, and writing. My graduate supervisor Dr. Goldreich made major contributions to the experimental design and programming. An undergraduate thesis student, Shah Mehran Iqbal, assisted in the data collection and statistical analysis for the pilot phase of the research (not included in this thesis). Another undergraduate thesis student, Arielle Chan, assisted in the data collection for the pilot phase and for Experiments 2 and 3. Several undergraduate laboratory study students also assisted in the data collection: Soumya Saini, Kyle Gauder, Vy Ngo, Faiza Shafaqat, Hiral Patel, Kaitlyn Gonsalves, and Cecelia Dai. Chapter 3 I was involved in all aspects of this empirical research: experimental design, programming, data collection, statistical analysis, and writing. Dr. Daniel Goldreich contributed to the experimental design and provided guidance at every stage of the research. An undergraduate thesis student, Jessica Webber, assisted in the data collection and statistical analysis. Several undergraduate laboratory study students also assisted in the data collection: Tyler Czaniecki, Cecelia Dai, Adam Alic, Jenin El-Sayes, Shirley Ong, and Claudia Turco. Chapter 4 I was involved in all aspects of this modeling research: conceptualizing, programming, running simulations, collecting data, performing statistical analysis, and writing. Dr. Daniel Goldreich provided guidance at every stage, and made major contributions to the conceptualizing and programming. An undergraduate thesis student, Michael Wan, assisted in running simulations and collecting data. vi Ph.D. Thesis – Li, L. McMaster University - Psychology Acknowledgements First and foremost, I would like to thank my graduate supervisor, Dr. Daniel Goldreich, for his guidance, support, and encouragement all these years. Dan is a wonderful mentor. His scientific enthusiasm is contagious. His devotion to research and education is inspiring. He is the type of researchers who find fulfillment in the purest pursuit of scientific discovery. He is also one of the nicest and most patient people I have met. I would like to extend my gratitude to my committee members, Drs. Deda Gillespie, Patrick Bennett, and David I. Shore, for their time, invaluable advice, and kindness that guide me through this rite of passage. I would also like to thank Dr. Jeffrey Min-in Yau, for his thoughtful feedback on this dissertation and his advice on finding the personal path in academia and science. Some of my happiest moments in grad school were thanks to the company of my former lab mates, Drs. Andy Bhattacharjee, Jonathan Tong, Ryan Peters, and particularly, Mike Wong. I miss our laughter and little adventures together. I would also like to thank my current lab mates, Arnav Bharadwaj, Kyle Gauder, Akash Deep, and Nina Prodribaba, for continuing the merry lab spirit and their helpful comments on my manuscript. My experimental work would not have been possible without the assistance of many undergraduate students over the years, to whom I am grateful: Arielle Chan, Jessica Webber, Tyler Czaniecki, Shah Mehran Iqbal, Michael Wan, Soumya Saini, Cecelia Dai, Vy Ngo, Faiza Shafaqat, Hiral Patel, Adam Alic, Jenin El-Sayes, Kaitlyn Gonsalves, Shirley Ong, and Claudia Turco. During my PhD and life journey in Canada, many friends have lent me an ear and perked me up when I felt down. Their emotional support helped me push through. In addition to my lab mates, I would like to give specific thanks to Savitri Jetoo and Alan Santinele Martino. There are too many other names to mention explicitly, but know that I thank you in my heart. In the past a few years, the person who has been the closest to me, sharing both joy and tears with me, is my partner Trevor Copp. Trevor, thank you for having my back. You make me a better person, and you make these all possible. After being a foreigner in Canada for 11 years, you are where I call home. I’ll extend my gratitude to Trevor’s lovely family: You are my family in Canada. I would like to dedicate this dissertation to

Load more