Beyond the Striate Cortex

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.