Perception

Psy391h - Classes 7-9

(This page last updated 31 Jan 2006.)
 

Stages of the Visual System

Most of the information below comes from studies of macaque visual cortex.

Retina

• photoreceptors
  • density decreases toward peripher
  • rods vs. cones
  • color coding in cones
    • 3 types, additive color mixture
• retinal ganglion cells
  • center surround organization

Lateral Geniculate Nucleus

• 6 layers
  • 2 magnocellular
    • faster responses
  • 4 parvocellular
    • includes color
  • segregated by eye

Primary Visual Cortex (V1, area 17)

• inputs in layer 4C
  • magnocellular 4C alpha, and then to 4B
  • parvocellular 4C beta, and then to 2 and 3
• ocular dominance
• orientation selectivity
• blobs in layers 2 and 3
  • responsive to color

Area V2

• magnocellular input to thick stripes
• input from blobs to thin stripes
• input from interblob regions to interstripes

Summary of Pathways

• magnocellular
  • LGN layers 1 & 2
  • V1 input 4C alpha, then to 4B
  • V2 thick stripes
  • on to dorsal pathway
  • carries information about motion
• parvocellular
  • LGN layers 3-6
  • V1 input 4C beta, then to layers 2 and 3
  • splits into blobs and interblob regions
  • blobs
    • color info
    • V2 thin stripes
  • interblob regions
    • orientation and form info
    • V2 interstripes
  • on to ventral pathway

Mapping Visual Areas in Human Cortex with fMRI

• Stimuli shifting position approx every 8 seconds
• Track wave of activity moving across cortex
• Similar layout to macaque cortex, but important differences

Specialization of Visual Areas

• Motion in area MT/V5
  • Damage can produce akinetopsia
• Color in area V4 in macaque, area V8 in humans
  • Damage can produce achromotopsia
• Separation of functions across different visual areas and pathways not that clean
  • Described as "concurrent processing"

   

More primitive pathway from retina through superior colliculus

• responsive to location and motion
• no color info
• may be responsible for blindsight

Auditory System

From Ear to Cortex

• cochlea
• auditory nerve
• midbrain structures, including inferior colliculus
• medial geniculate nucleus
• primary auditory cortex.

In these early stages, cell responses are driven by frequency.

• Primary auditory cortex is arranged according to frequency.

Determining location is more indirect in audition, depending on both the timing and the relative intensity of sounds arriving at the two ears.

next: Object Recognition

Psych 391h: Cognitive Neuroscience Kyle Cave Psychology Dept. U. Mass.