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Sensation & Perception Ch. 4: The Visual Cortex and Beyond © Takashi Yamauchi (Dept. of Psychology, Texas A&M University) Main topics Spatial layout Columns, location, orientation & ocular dominance Pathways for what, where and how Modularity: faces, places & bodies Evolution and plasticity ch 4 1 Processing past the retina • LGN (lateral geniculate nucleus) • V1 (Primary visual cortex/striate cortex) ch 4 2 ch 4 3 General principles • Functional segregation • Divide and conquer ch 4 4 ch 4 5 Lateral Geniculate Nucleus Image courtesy of Dr. Paul Wellman ch 4 6 LGN • Input & output • Organization of LGN – 2 types – 6 layers in total • Retinotopic map ch 4 7 Input & output to and from LGN T: thalamus L: Other LGN neurons ch 4 8 The organization of LGN • LGN has 6 layers: ch 4 9 ch 4 10 LGN has 2 types of main layers: • Parvocellular layers • Magnocellular layers ch 4 11 Why different layers? • What distinguishes these layers? • Any guess? Functional differences: Magnocellular Layers: carry information necessary to detect motion Parvocellular Layers: carry information necessary to detect color, fine textures and patterns. ch 4 12 What does this tell? • The human brain perform many specialized tasks. • The human brain is organized functionally. ch 4 13 The Striate Cortex (V1) ch 4 14 V1 (Striate Cortex) Image courtesy of Dr. Paul Wellman ch 4 15 ch 4 16 V1 (Striate Cortex) • Main characteristics: – Functional specialization and columnar organization • What functions? Any guess? •Neurons in V1 are specialized to respond to specific aspects of stimuli. •Neurons in V1 can detect a line and its orientation. •Neurons in V1 are organized in columns. ch 4 17 Single cell recording ch 4 18 Detecting a line and its orientation? ch 4 19 Detecting a line and its orientation? A particular neuron(s) in V1 respond only when the line has a specific orientation. ch 4 20 Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the Wadsworth Group, a division of Thomson Learning Simple cortical cell receptive field ch 4 21 ch 4 22 • Video • Single Cell Recording – Hubel & Wiesel • http://www.youtube.com/watch?v=IOHayh06LJ4 &feature=related ch 4 23 Neurons in Striate Cortex - continued • Complex cells – Like simple cells • Respond to bars of light of a particular orientation – Unlike simple cells • Respond to movement of bars of light in specific direction ch 4 24 Neurons in Striate Cortex - continued • End-stopped cells – Respond to: • Moving lines of specific length • Moving corners or angles – No response to: • Stimuli that are too long ch 4 25 3 types of neurons in V1 • Simple cells – Detect lines and their orientations • Complex cells – Detect lines, their orientations and their movement • End-stopped cell – Fire to moving lines of a specific length ch 4 26 ch 4 27 V1 (Striate Cortex) Image courtesy of Dr. Paul Wellman ch 4 28 Representing spatial layout • Retinotopic map preserving the spatial layout of a stimulus • LGN and V1 (primary visual cortex) show a retinotopic map. ch 4 29 Cortical magnification factor • Fovea accounts for .01% of retina • Signals from fovea account for 8% to 10% of the visual cortex Retina V1 (primary visual cortex) fovea ch 4 30 ch 4 31 Fig. 2.11, p.53 Selective adaptation of neurons • Neurons are like specialized feature detectors. – They detect particular perceptual properties of stimuli • E.g., brightness, direction, color, size, orientation, • Neurons tuned to specific stimuli fatigue • Neuron’s firing rate decreases ch 4 • This causes a modification of perception. 32 Demonstration • Contrast sensitivity • Waterfall illusion ch 4 33 Selective adaptation to size ch 4 34 ch 4 35 ch 4 36 ch 4 37 Narrow-bar neurons wide-bar neurons ch 4 38 Narrow-bar neurons fatigued wide-bar neurons fatigued ch 4 39 ch 4 40 Selective adaptation to orientation ch 4 41 ch 4 42 ch 4 43 Organization of V1 • Columnar organization – Orientation columns – Location columns – hypercolumns ch 4 44 ch 4 45 V1 LGN ch 4 46 Ocular dominance columns Visual information from different eyes is stored in separate columns in an alternate manner ch 4 47 ch 4 48 Higher-level visual processing • The brain processes increasingly more complex visual information separately. • And then combine them together. ch 4 49 Pathways for what, where, and how ch 4 50 Two visual pathways (what & where/how systems) ch 4 Image from Neuroscience, 2nd Ed. (2000). 51 Two visual pathways • The information about “what” and the information about “where” & “how” is segregated. • Video clip: “The Brain: Vision & Motion” (1995) ch 4 52 Lesion studies • Removing a particular part of a brain. • Test what happens after the removal. ch 4 53 The monkey had to select the correct object to get the food reward Object discrimination task Landmark discrimination task ch 4 The monkey had to select the food well close to the 54 cylinder. Double dissociation ch 4 55 Object discrimination task Can’t do the object discrimination task but can do the landmark discrimination task Landmark discrimination task Can’t do the landmark discrimination task but can do the object discrimination task ch 4 56 Two visual pathways (where & what systems) ch 4 Image from Neuroscience, 2nd Ed. (2000). 57 Two visual pathways (how & what systems) ch 4 Image from Neuroscience, 2nd Ed. (2000). 58 Two visual pathways (how & what system) Patient D. F had bilateral damage to the ventral path. Carbon monoxide poisoning at age 35. ch 4 59 Two visual pathways (how & what system) D. F Control Matching task: match the orientation of the card to that of the slot. Posting task: The orientation of the slot was changed in each trial. Post the card into the slot. ch 4 60 • NPR: Blind man sees with subconscious eye (12/23/08); Interview and video record – http://www.npr.org/templates/story/story.ph p?storyId=98590831 • A blind man who damaged the occipital lobe can still navigate and walk without bumping into objects. ch 4 61 Modularity: structures for faces, places, and bodies ch 4 62 Feature detectors • Neurons that fire to specific features of a stimulus • Pathway away from retina shows neurons that fire to more complex stimuli • Cells that are feature detectors: – Simple cortical cell – Complex cortical cell – End-stopped cortical cell ch 4 63 Single cell recording of neurons in the temporal lobe An electrode is inserted here, and neural responses are measured when stimuli are changed gradually ch 4 64 ch 4 65 Neurons in this area respond to complex stimuli like those shown on the left. ch 4 66 Modularity: Structures for Faces, Places, and Bodies – Inferotemporal (IT) cortex in monkeys • One part responds best to faces while another responds best to heads • Results have led to proposal that IT cortex is a form perception module – Temporal lobe damage in humans results in prosopagnosia ch 4 67 Figure 4.18 (a) Monkey brain showing location of the inferotemporal cortex (IT) in the lower part of the temporal lobe. (b) Human brain showing location of the fusiform face area (FFA) in the fusiform gyrus, which is located under the temporal lobe. ch 4 68 Prosopagnosia • • • • Episode from “The man who mistook his wife for a hat” Video: Mind Eye Also see “The man who mistook his wife for a hat” by Oliber Sacks. ch 4 69 ch 4 70 Can copy them but can’t name them ch 4 71 ch 4 72 ch 4 73 Copies of the black (A) and the white (B) vertical contour. Copies of the black (A) and the white (B) diagonal contour. ch 4 74 Copies of the left subfigure (A) The right subfigure (B) And the central subfigure (C) ch 4 75 How do neurons become specialized? • Experience-dependent plasticity in humans – Experience causes changes in how neurons are tuned. ch 4 76 Figure 4.24 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Brain responses ch 4to Greebles and faces before and after 77 Greeble training.