S&P 070305 - Singh 301 LEC 10 Classes of cells Simple...

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Singh / 301 LEC 10 Classes of cells: Simple cells: Respond to edges and bars of specific orientations. Elongated RFs with clearly-demarcated ON and OFF regions Require exact positioning of edge or bar within RF Complex cells: Also orientation selective However RFs do not have clearly-defined ON and OFF regions. Exact positioning of edge or bar within RF is not needed. "Hypercomplex cells": Respond to specific orientation and specific bar lengths 'End-stopped' versions of simple and complex cells Sensitive to sharp corners and points of high curvature along contours 2., Selectivity for direction of motion Given a bar of the optimal orientation, a cell will respond more strongly to a particular direction of motion through the RF (but cannot distinguish between object motion and eye/head motion) 3. Binocularity First site of binocular cells (have two RFs -- one in each eye) Exhibit ocular dominance (slightly stronger response to one eye) Sensitive to small positional differences between the two eyes (basis for stereovision) 4. Size selectivity Variation in RF size: depends on distance from fovea (preference for bars of different widths) End-stopped cells: tuned to specific bar lengths 5. Color Blob cells (inputs from LGN parvo layers); weaker orientation selectivity Exhibit color opponency Columns and Hypercolumns Results of measuring orientation preference with orhogonal and tangential penetration with a microelectrode Orthogonal: no change in preferred orientation Tangential: systematic variation in preferred orientation Ice-cube Model Columns -- combination of orientation preference and ocular dominance Orientation slabs (columns representing different orientations) Ocular dominance slabs (columns exhibiting left-eye and right-eye dominance) Hypercolumns LEC 11 Beyond V1 Visual information is processed along two separate pathways or streams
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  • Spring '07
  • Singh,M.
  • difference threshold, stimulus intensity, Gustav Fechner, order Difference Threshold, stimulus Absolute Threshold

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S&P 070305 - Singh 301 LEC 10 Classes of cells Simple...

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