UNDERSTANDING AND IMPROVING DEPTH PERCEPTION FROM MOTION PARALLAX IN OLDER ADULTS A Dissertation Submitted to the Graduate Faculty of the North Dakota State University of Agriculture and Applied Science By Jessica Marie Holmin In Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Department: Psychology March 2016 Fargo, North Dakota North Dakota State University Graduate School Title Understanding and Improving Depth from Motion Parallax in Older Adults By Jessica Marie Holmin The Supervisory Committee certifies that this disquisition complies with North Dakota State University’s regulations and meets the accepted standards for the degree of DOCTOR OF PHILOSOPHY SUPERVISORY COMMITTEE: Mark Nawrot Chair Linda Langley Melissa O’Connor Michael Robinson Approved: 3/30/2016 James Council Date Department Chair ABSTRACT Successful navigation in the world requires effective visuospatial processing. Unfortunately, older adults have many visuospatial deficits, which can have severe real-world consequences. It is therefore crucial to understand and try to alleviate these deficits whenever possible. One visuospatial process, depth from motion parallax, has been largely unexplored in older adults. Depth from motion parallax requires retinal image motion processing and pursuit eye movements, both of which are affected by age. Given these deficits, it follows logically that sensitivity to motion parallax may be affected in older adults, but no one has yet investigated this possibility. The goals of the current study were to characterize depth from motion parallax in older adults, to explore the mechanisms by which age might affect depth from motion parallax, and to develop training programs that might alleviate the effects of age on motion parallax. In Experiment One, older and younger adults’ motion parallax depth thresholds were characterized. Motion thresholds and pursuit accuracies were also measured. The results of Experiment One revealed that older adults had higher MP depth thresholds than younger adults, and that these age changes were primarily driven by age changes in pursuit eye movements. In Experiment Two, older adults were provided with motion and pursuit training programs to use at home, following the logic that training in motion and pursuit would improve older adults’ depth thresholds. Improvements of performance at these training tasks were assessed. Depth thresholds, motion thresholds, and pursuit accuracy pre- and post-training were evaluated as well, using the same methods as in Experiment One. The results of Experiment Two revealed that motion and pursuit training did not affect observers’ performance throughout the course of training, and there were no effects of training on depth or motion thresholds or pursuit eye movements. The current study is the first to examine age changes in motion parallax depth thresholds, and to investigate the iii mechanisms of age changes in the perception of depth from motion parallax. Though the training programs in Experiment Two did not produce improvements of perceptual performance, this study was successful in implementing an easy-to-use, at-home training technique. iv ACKNOWLEDGEMENTS There are many people who were instrumental in the successful completion of this dissertation. First, I’d like to thank my two mentors, Dr. Mark Nawrot and Dr. Farley Norman, for teaching me pretty much everything I know about doing good science. I’d also like to thank my committee, Dr. Linda Langley, Dr. Melissa O’Connor, and Dr. Michael Robinson, for their valuable feedback on my dissertation proposal. Special thanks go to Dan Gu of the CVCN— without his formidable programming powers, I might have never succeeded in completing this project. Along with the people directly involved in the completion of this dissertation, there are also many people who provided me with the moral and social support I needed to succeed. To my father, stepmother, grandmother, and siblings: thank you for believing in me, and supporting my move to Fargo. I especially would like to thank my mother and my best friend Ashley, for their constant love and encouragement, and for showing a curiosity about my research that is rarely found outside of academia. I believe that, to succeed in graduate school, one needs to find support within the graduate school community. Shanda, Andrew, Andrea, and Christina have provided me with that support. We have commiserated in our downfalls and celebrated our accomplishments together, and provided valuable advice to one another. My graduate school experience would not have been the same without them. Lastly, I’d like to thank the people who made my transition from Kentucky, where I was born and raised, to Fargo, where I didn’t know a soul, more bearable: Deirdre, for being one of my first friends in Fargo; my book club friends, Amanda, Felix, Alyson, Little Amanda, and v Jamie, for giving me an excuse to do two of my favorite things (overeat and talk about books); and Mark and Lisa Nawrot, for welcoming me into their home for Thanksgiving every year. vi TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii ACKNOWLEDGMENTS .............................................................................................................. v LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ........................................................................................................................ x LIST OF ABBREVIATIONS ........................................................................................................ xi INTRODUCTION .......................................................................................................................... 1 Aging and the Visual System .............................................................................................. 2 Aging and Motion Processing ........................................................................................... 29 Aging and Pursuit Eye Movements .................................................................................. 42 EXPERIMENT ONE .................................................................................................................... 58 Aging and Motion Parallax ............................................................................................... 58 The Current Study ............................................................................................................. 71 Method .............................................................................................................................. 71 Results ............................................................................................................................... 78 Discussion ......................................................................................................................... 84 EXPERIMENT TWO ................................................................................................................... 87 Aging and Perceptual Learning ........................................................................................ 89 Eye Movement Training ................................................................................................. 103 The Current Study ........................................................................................................... 106 Method ............................................................................................................................ 107 Results ............................................................................................................................. 113 Discussion ....................................................................................................................... 120 vii GENERAL DISCUSSION ......................................................................................................... 124 REFERENCES ........................................................................................................................... 127 APPENDIX A. HEALTH QUESTIONNAIRE .......................................................................... 156 APPENDIX B. TRAINING INSTRUCTIONS .......................................................................... 157 APPENDIX C. EQUIPMENT AGREEMENT FORM .............................................................. 159 viii LIST OF TABLES Table Page 1. Demographic Characteristics of Experimental Groups .......................................................... 107 ix LIST OF FIGURES Figure Page 1. Parallel pathways in the visual system ...................................................................................... 18 2. Old neural model of the smooth pursuit eye movement system ............................................... 48 3. New neural model of the smooth pursuit eye movement system ............................................. 49 4. MP diagram ............................................................................................................................... 65 5. Schematic of the stimulus used in the depth threshold task ...................................................... 74 6. Threshold dθs for younger and older observers ........................................................................ 79 7. Depth thresholds (dθ/dα) for younger