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Lecture 8

PSC 131 Lecture 8: Objects and Faces

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PSC 131
Geng Joy

I. Lecture 8 – Objects and Faces (May 1, 2017) A. Class Summary 1. After V1: What vs Where Pathways a. Recognition vs Action 2. Object Recognition a. Templates and structural descriptions 3. The special case of faces 4. Scenes (end of Chapter 7) B. What vs Where/How Pathways 1. The main visual areas of the macaque monkey cortex a. Divergence of information along the ventral (lower, what pathway) and dorsal (higher, where pathway) 2. Object Recognition Retina (ganglion cells)  LGN (relay station of thalamus and V1)  V1 (bars of light)  path to V4, MT, TEO, TE (greater functional specialization) a. Different neurons in different areas of the brain perform different functions b. The cartoon is very clear and sparse 3. A partial “wiring” diagram for the main visual areas of the brain a. Massively complex in what info regions calculate and how their interacting with other regions 4. Ungerleider and Mishkin a. Lesion different parts of monkeys’ brains and have monkeys perform the same tasks i. Object discrimination (tell the difference between purple triangle and green prism ii. Pick the object that had distance relation to a landmark iii. Understanding what the object is they’re looking for OR where the object is relative to the food wells b. Double dissociation between lesion site (temporal or parietal cortex) and task performance (object or spatial discrimination i. Two different brain regions have one ability unaffected but another ability affected from the lesion c. Monkeys had intact visual systems; either discriminated what the object was OR where the object was, but not both i. Temporal lesions: Good spatial (where) , bad discrimination (what) ii. Parietal - good object discrimination (what) , bad spatial task (where) iii. Neither of these brain lesions are important for generally getting object, but shows area specialization 5. Visual Agnosia – failure to recognize objects in visual domain that cannot be attributed to a deficit in primary sensory processing; recognition can be made with other modalities such as audition or smell, or through other sources of information (e.g. actions) a. Can identify named objects, but cannot generate name to seen object (recognition) b. Frequently with bilateral occipitotemporal damage i. Perhaps some hemispheric differences for different sub-types c. Ex: Patient D.F. cannot recognize objects, but knows how to act on them [image] i. What something is and where and how to act on something in space ii. Had DF take a card and test if she knows how to match the mail slot iii. Explicit matching task – difficult for her to explain what it is to match it iv. Action task – told her to put the letter in the slot (she could do it fine, but she was not asked to recognize)  Motor skills easier to execute than describe/explain 6. Dissociation of Action with Recognition a. Language, ability to move, ability to see is intact – but has visual agnosia b. Has difficulty describing the object (clarinet) c. Uses tactile clues, uses his hands – verbal system drives motor system i. Verbal system is what he’s most aware of; motor system comes through and is more aware ii. Distinction : know what something is and knowing how to use something/where it is C. Object Recognition 1. Response of V4 Cells a. If a neuron fires more when there’s a stimulus, it doesn’t mean it prefers one stimulus over another b. People have tried to use different strategies, sometimes 2. An example of using a genetic algorithm to discover what a cell in the “what” pathway of the temporal lobe might respond to: a. They take the image and create versions of it to see what the neuron likes the most (process of deduction) 3. Selectivity – areas of the human visual cortex specialized for faces, places, body parts, and motion a. You find robust segregation and specialization for these different classes of objects b. Fusiform Face Area (heads, faces); Parahippocampal Place Area; Extrastriate Body Area (arms and legs), Middle Temporal (movement) 4. Templates a. Simplest model of recognition is that we have image-
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