A Functional Model for Primary Visual Cortex Nastaran Hesam Shariati A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy Discipline of Biomedical Science Faculty of Medicine The University of Sydney Acknowledgements My utmost gratitude goes to God, the Almighty, without whose mercy and blessing, this work would not have been possible. I would like to express my sincere gratitude to my supervisor Dr. Alan Freeman, for his invaluable guidance, many fruitful discussions and constant support in making this research possible over the years. I would like to thank my associate supervisor Dr. Aaron Camp for his guidance, and help during my thesis writing. My deep appreciation goes to my associate supervisor and friend Dr. Jin Huang for her continuous support, encouragement and advice during my stressful moment. I offer my regards to Prof. Fazlul Huq and Dr. Peter Knight for their valuable support and advices. My special appreciation is extended to my beloved husband who was given me the reason, encouragement and inspiration to continue my work during the most stressful time of my life. To whom he was patient with me and understands my moodiness, allowing me to cover the whole house with my papers and books. To you, I dedicate this thesis. I would like to express my respect and sincere gratitude to the lovely, and kind technical and admin staff at Bio – Felicia, Ruth, Ann, Gautham, Natasha, Helen and Tuyet – for creating a nice, helpful and supportive environment for students. I am in debt to my lab mates, Munira, Padma and Elaine, for making the laboratory such an enjoyable environment to work in. My special thanks to my best friend, Paul, for his friendship and his constant technical support. My heartfelt thanks are for my father and mother who keep supporting me from far by their precious encouragement. To my sisters and brother for their continuous support and encouragement throughout my study. I would like to thank my angel daughter, Helia, who understood that I am under pressure especially during my thesis writing and tried to encourage me with her heartfelt hugs. To whom she was the initial reason to step on this path. iii Brief Contents ACKNOWLEDGEMENTS ................................................................................................................ III BRIEF CONTENTS .............................................................................................................................. V DETAILED CONTENTS .................................................................................................................. VII SUMMARY ...........................................................................................................................................XI CHAPTER 1. BACKGROUND ........................................................................................................ 1 CHAPTER 2. AIMS ......................................................................................................................... 57 CHAPTER 3. METHODS ............................................................................................................... 61 CHAPTER 4. RECEPTIVE FIELDS AND ORIENTATION SELECTIVITY ......................... 67 CHAPTER 5. DIRECTION SELECTIVITY ................................................................................ 83 CHAPTER 6. SIMPLE AND COMPLEX CELLS ....................................................................... 99 CHAPTER 7. SPATIAL FREQUENCY SELECTIVITY .......................................................... 107 CHAPTER 8. DISCUSSION ......................................................................................................... 111 REFERENCES ................................................................................................................................... 119 APPENDIX A. EQUATIONS ............................................................................................................ 129 APPENDIX B. PARAMETER SETTINGS ..................................................................................... 139 APPENDIX C. PUBLICATIONS ..................................................................................................... 151 v Detailed Contents ACKNOWLEDGEMENTS ................................................................................................................ III BRIEF CONTENTS .............................................................................................................................. V DETAILED CONTENTS .................................................................................................................. VII SUMMARY ...........................................................................................................................................XI CHAPTER 1. BACKGROUND ........................................................................................................ 1 1.1. RETINA ................................................................................................................................... 3 1.2. LATERAL GENICULATE NUCLEUS............................................................................................ 6 1.3. RETINA TO GENICULATE CONNECTION ................................................................................... 6 1.4. SIMPLE AND COMPLEX CELLS IN THE PRIMARY VISUAL CORTEX ............................................. 7 1.4.1. Laminar location and synaptic connections ..................................................................... 9 1.4.2. Cortical responses .......................................................................................................... 10 1.4.3. Spatial receptive field ..................................................................................................... 13 1.4.4. Quantitative measurements............................................................................................. 16 1.4.5. Models ............................................................................................................................ 21 1.4.5.1. Feed-forward model ............................................................................................................ 22 1.4.5.2. Recurrent model .................................................................................................................. 24 1.5. ORIENTATION SELECTIVITY .................................................................................................. 26 1.5.1. Qualitative measurement ................................................................................................ 26 1.5.2. Quantative measurements ............................................................................................... 27 1.5.3. Orientation selectivity mechanism .................................................................................. 30 1.5.4. Orientation selectivity model .......................................................................................... 32 1.5.4.1. Feed-forward models .......................................................................................................... 32 1.5.4.2. Inhibitory models ................................................................................................................ 35 vii 1.5.4.3. Recurrent model .................................................................................................................. 37 1.5.4.4. Anisotropic LGN-driven recurrent model ........................................................................... 38 1.6. DIRECTION SELECTIVITY ...................................................................................................... 40 1.6.1. Qualitative measurement ................................................................................................ 40 1.6.2. Quantative measurements ............................................................................................... 42 1.6.3. Direction selectivity mechanism ..................................................................................... 43 1.6.4. Direction selectivity model ............................................................................................. 47 1.7. SPATIAL FREQUENCY SELECTIVITY ...................................................................................... 53 1.7.1. Spatial selectivity mechanism ......................................................................................... 55 CHAPTER 2. AIMS ......................................................................................................................... 57 2.1. OBJECTIVES OF THE RESEARCH ............................................................................................ 57 2.2. ORGANIZATION OF THE THESIS ............................................................................................. 58 CHAPTER 3. METHODS ............................................................................................................... 61 3.1. MODEL STRUCTURE.............................................................................................................. 61 3.2. STIMULI ............................................................................................................................... 64 3.3. IMPLEMENTATION ................................................................................................................ 64 CHAPTER 4. RECEPTIVE FIELDS AND ORIENTATION SELECTIVITY ......................... 67 4.1. AIM .....................................................................................................................................