An Introduction to the Visual System

Brain organisation 2 Why is the cerebral cortex a sheet? 4 Cortical origami 6 Does connectivity predict intelligence? 7 Analysis techniques: mapping the brain 8 Structural imaging 8 Functional imaging techniques: PET and fMRI 10 What is the relationship between blood flow and neural activity? 12 The resolution problem 13 Measuring brain activity in real time: MEG and EEG 14 Transcranial magnetic stimulation (TMS) 15 Summary of key points 16 2 The eye and forming the image 18 What is the eye for? 18 Light 18 The structure of the eye 19 Focusing the image 25 The development of myopia 26 Clouding of the lens (cataracts) 28 Photoreceptors 28 Transduction 30 The calcium feedback mechanism 31 Signal efficiency 32 The centre-surround organisation of the retina 33 Light adaptation 36 Duplicity theory of vision 37 Sensitivity, acuity and neural wiring 40 Summary of key points 41 3 Retinal colour vision 44 Why do we need more than one cone pigment? 44 Trichromacy 44 The genetics of visual pigments 47 The blue cone pigment 53 Rhodopsin and retinitis pigmentosa Making a complex process seem simple 62 The retina 63 The lateral geniculate nucleus (LGN) 63 The primary visual cortex (VI) 64 Visual area 2 (V2) 67 Visual area 4 (V4) 68 Visual areas 3 (V3) and 5 (V5) 69 The koniocellular pathway 69 The functional organisation 70 Perception vs. action 71 Blindsight 73 Summary of key points 76 5 Primary visual cortex 78 The visual equivalent of a sorting office? 78 Segregation of layer 4 inputs 79 Cortical receptive fields 79 Spatial frequency 81 Texture 82 Direction selectivity 82 Colour 84 Modular organisation 84 Summary of key points 87 6 Visual development: an activity-dependent process 89 Variations on a theme 89 Monocular or binocular deprivation 91 Image misalignment and binocularity 93 Image misalignment in humans 94 Selective rearing: manipulating the environment 96 Impoverished visual input in humans 98 The critical period 98 What we see, shapes how we see it 99 Summary of key points