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Beyond the Striate Cortex

Beyond the Striate Cortex . Extrastriate Pathways. Parallel processing of visual information from the striate cortex. Three pathways: Color processing – P blob cells, goes from V1 to V2, then V4, then inferior temporal cortex.

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Beyond the Striate Cortex

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  1. Beyond the Striate Cortex

  2. Extrastriate Pathways • Parallel processing of visual information from the striate cortex. • Three pathways: • Color processing – P blob cells, goes from V1 to V2, then V4, then inferior temporal cortex. • Shape processing, depth perception – P interblob cells, go from V1 to interior temporal cortex. • Motion & spatial relations – M cells, V1 to V2, then MT (V5), to parietal cortex.

  3. Equiluminance • Holding brightness constant permits the study of the contribution of color to perception. • Results: • Brightness, not color, is important to motion detection, perspective, relative sizes, depth perception, figure-ground relations, visual illusions. • Motion is a cue for distinguishing among objects. • Things that move together belong together.

  4. Complex Forms, Motion • Processing of form occurs outside the visual cortex – inferior temporal cortex. • Not organized retinotopically. • 10% selective for specific images (hands, faces). • Processing of motion occurs in middle temporal area (MT or V5), then parietal lobe. • Used for seeing moving objects, pursuit eye movements, guidance of bodily movement

  5. Visual Agnosias • Existence of distinct agnosias for aspects of perception suggests that these abilities are localized to areas selectively damaged. • Achromatopsia – good perception of form despite inability to distinguish hues. • Prosopagnosia – inability to recognize faces as particular people (identity). Can recognize that it is a face, and tell the parts.

  6. Visual Illusions • Vision is not simply the processing of inputs from the retina. • Interpretation of visual input is learned. • Infants and depth perception • Visual illusions demonstrate that experience and expectations also influence the percept. • Attention can determine what we see – gestalt reversals.

  7. Binding Mechanisms • How is information from the separate, parallel pathways brought together and associated? • Cells may identify patterns of synchronous activity. • Treisman & Julesz – combination requires attention. • A pre-attentive process detects the major outline of an object. • An attentive process notices, selects & highlights combinations of features.

  8. Development of the Visual System • Pathways are developed before birth. • Fovea develops in the first four months after birth – ability to see detail. • Connections between layers in visual cortex develop with experience, after birth. • Visual acuity becomes adult-like by 12 months.

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