Central Visual Processes

Anthony J Greene2 Central Visual Pathways I.Primary Visual Cortex Receptive Field Columns Hypercolumns II.Spatial Frequency III.Nerve or Cortical Damage IV.Higher Visual Areas

Anthony J Greene3 Occipital Lobe

Anthony J Greene4 Occipital Lobe: Calcarine Sulcus -- V1 -- Striate Cortex

Anthony J Greene5 Cells in V1

Anthony J Greene6 Single-Cell Recording (Hubel & Weisel, 1962) Attempted to discover what sorts of information cells in (cat) V1 respond to Accidentally discovered orientation specific cells organized into columns and hypercolumns V1

Anthony J Greene7

8 Cells In V1 Cells in V1 receive messages from certain ganglion cells such that they respond to stimuli of a certain orientation from a small portion of the retina - Orientation Specific ~ 200 Million Cells in V1 Inputs from Ganglion Cells

Anthony J Greene9 Cells In V1 One V1 cell receives inputs from many ganglion cells One ganglion cell may send inputs to numerous V1 cells Stimuli from every possible orientation, and from every position in the visual field are detected by different cells in V1 Simple Cells detect only orientation -- Complex Cells detect orientation and motion

Anthony J Greene10 How to Make a Complex Cell Orientation specific inputs from ganglion cells is similar to simple cells However, the receptive field is much larger and is designed to respond maximally when inputs from sub-fields are sequential

Anthony J Greene11 Cells in V1 Occular Dominance

Anthony J Greene12 Columns in V1

Anthony J Greene13 Organization of Cells in V1 Columns are sections of cortex which all respond to the same orientation from approximately the same region of cortex

Anthony J Greene14 Organization of Cells in V1 Hypercolumns are groups of columns, from both eyes, which are influenced by the same minute portion of the visual field

Anthony J Greene15 Organization of Cells in V1 What sort of information are these cells detecting? Is the information from any single cell in V1 informative?

Anthony J Greene16 Response Properties of Cells in V1 The extent to which columns will respond to stimuli with no interactions from other columns Orientation Column Position on Occular Dominance Slab Cellular Activity

Anthony J Greene17 Lateral Inhibition The column with the strongest response to a given stimuli will suppress the respondse of neighboring columns + -

Anthony J Greene18 Response Properties of Cells in V1 The extent to which columns will respond to stimuli with lateral inhibition from other columns Orientation Column Position on Occular Dominance Slab Cellular Activity

Anthony J Greene19 Processing at V1 Is Edge Detection

Anthony J Greene20 Edge Detection While lateral inhibition normally improves the accuracy of edge detection, in this case it creates the “Deli Wall Illusion”

Anthony J Greene21

Anthony J Greene22 Understanding Acuity: Spatial Frequency Analysis Measuring visual acuity: –Eye doctors use distance (e.g., 20/20) –Vision scientists use visual angle

Anthony J Greene23 Understanding Acuity: Spatial Frequency

Anthony J Greene24 Understanding Acuity: Spatial Frequency

Anthony J Greene25 Describing Processes in V1: Spatial Frequency Analysis

Anthony J Greene26 Describing Processes in V1: Spatial Frequency Analysis (cont.) Orientation Frequency Contrast Decreasing Contrast

Anthony J Greene27 Spatial Frequency Analysis (cont.) Fourier - French mathematician, came up with theory that one can create any complex wave through a summation of Sinusoids (or sub-parts, sub-waves) Fourier Analysis divides all orientation specific cells in V1 according to the width of their receptive fields or Spatial Frequency 1) Low 2) Medium 3) High

Anthony J Greene28 Spatial Frequency Analysis (cont.) Neurons can then be viewed as Spatial Filters which separately analyze differing levels of detail or scale Any scene can then be decomposed into images with varying spatial frequencies - low frequency images are blurry and only the most prominent features are represented - high frequency images exaggerate the fine details Construing form vision in terms of an emergent property of these different scales of receptors is referred to as the Multichannel Model

Anthony J Greene29 Spatial frequency Analysis (cont.)

Anthony J Greene30 Spatial frequency Analysis (cont.)

Anthony J Greene31 Spatial frequency Analysis (cont.) Once divided by width, cells can further be grouped according to their orientation specificity This allows a vastly simplified organization of neural activity - 3 major variables - Spatial Frequency, Orientation & Contrast Additionally, Fourier analysis helps explain how individual cells may contribute information to the aggregate

Anthony J Greene32 Spatial frequency Analysis (cont.)

Anthony J Greene33 Spatial frequency Analysis (cont.)

Anthony J Greene34 Spatial Frequency Analysis (cont.) 1f gives the fundamental waveform 2f... xf : are called harmonics - increasing details

Anthony J Greene35 Spatial Frequency Analysis (cont.)

Anthony J Greene36 Spatial Frequency Illusions

Anthony J Greene37 Spatial Frequency Illusions

Anthony J Greene38 Spatial Frequency Illusions

Anthony J Greene39 Spatial Frequency Illusions

Anthony J Greene40 Color at V1 Among cells selective for orientation are patches of cells selective for color (and not orientation), which are known as Blobs. Other cell (orientation specific cells) regions are known as interblobs.

Anthony J Greene41 Organization of V2 Thin Stripes receive information from Blobs and pass it to V4 Thick Stripes recieve information from complex cells and send it to V5 and V3 Interstripes recieve information from simple cells and send it to V3 and V4 Information at V2 is 3-D

Anthony J Greene42 Nerve or Cortical Damage 1) Retina / Optic Nerve 2) Optic Chiasm 3) Optic Tract 4) V1/V2

Anthony J Greene43 Nerve or Cortical Damage Retina/Optic Nerve: Monocular blindness

Anthony J Greene44 Nerve or Cortical Damage Optic Chiasm: Nasal field blindness

Anthony J Greene45 Nerve or Cortical Damage Optic Chiasm: Bitemporal field blindness

Anthony J Greene46 Nerve or Cortical Damage Optic Tract/LGN/Radiations: Homonymous Blindness

Anthony J Greene47 Nerve or Cortical Damage V1: Quadrantic blindness

Anthony J Greene48 Nerve or Cortical Damage V1/V2: Scotoma Complete blindness case of Blindsight

Anthony J Greene49 Higher Visual Areas V3: Form & Dynamic Form V4: Color V5: Motion IT: What System: Object Recognition –Lingual Gyrus of IT: Face Recognition PP: Where System: Object Location and Navigation

Anthony J Greene50 Simplified Functional Visual Anatomy

Anthony J Greene51 Simplified Flow Diagram of the Visual System LGN Parvo Magno Thalamus Occipital Lobe Temporal Lobe Parietal Lobe V1 V2 V3 V4 V5 or MT IT Optic Nerve PP

Anthony J Greene52 Summary } } }

Anthony J Greene53