The architecture of the visual system: What is the grand design? April 12, 2010

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The architecture of the visual system: What is the grand design?

  • April 12, 2010

Goals of the visual system

  • Create a meaningful representation of the 3D world

  • Recognize objects

  • Detect motion, color, edges

  • Reconstruct 3D depth

  • Create representation of world useful for action

  • Store visual memories

  • Distinguish shadows from real edges

  • Suppress vision during saccades

  • How are all these different functions organized?

Mapping different visual areas

Mapping different visual areas

The What and Where Pathways

The Ungerleider & Mishkin (1982) Experiment

  • Task 1:

  • Object discrimination

    • study an object
    • select the familiar object (reward)

Challenges to What/Where

Milner and Goodale: “The A brain-damaged patient (D.F.) …has a profound inability to recognize objects, places and people, in large part because of her inability to make perceptual discriminations of size, shape or orientation, despite having good visual acuity.Yet she is able to perform skilled actions that depend on that very same size, shape and orientation information that is missing from her perceptual awareness.”

Konen and Kastner, “Two hierarchically organized neural systems for object information in human visual cortex” 2008

  • evidence from functional brain imaging in humans demonstrates that object representations are not confined to the ventral pathway, but can also be found in several areas along the dorsal pathway.

  • In both streams, areas at intermediate processing stages in extrastriate cortex (V4, V3A, MT and V7) showed object-selective but viewpoint- and size-specific responses.

  • In contrast, higher-order areas in lateral occipital and posterior parietal cortex (LOC, IPS1 and IPS2) responded selectively to objects independent of image transformations

We know very little about interactions between areas (lawrence…)

Interactions between areas

  • Functional connectivity (determine networks with significantly increased correlated activity; using seed-based and ICA techniques)

  • Granger causality (determine whether a lagged time course from area X can predict another time course from area Y)

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