Psy315 - Classes 7-9: The Visual System

(This page last updated 27 January, 2009.)


Properties of Individual Neurons


  • Inputs received at dendrites
  • Can be either excitatory (positive) or inhibitory (negative)
  • Inputs from many different synapses on dedrites are combined to determine output


  • All or none: fires only after input reaches threshold
  • Action potential travels full length of axon without losing strength
  • When it reaches end of axon, triggers release of neurostransmitters


The Eye


Pathway from Eye to Cortex


Primary Visual Cortex (area V1)


Cortical Visual Areas Beyond V1


Perception seems effortless to us, but our perceptual systems must work hard to impose an interpretation on the pereptual input.


  • completion of missing contours
  • ambiguous figures
    • Necker cube
    • Rubin's vase
    • duck/rabbit
    • etc.
  • effect of context on identification of ambiguous letters
  • low-quality figures that cannot be recognized at first
    • Once interpretation is known and in memory, it cannot be avoided.

All of these figures are ambiguous at first, but eventually your visual system is able to go beyond the information given to come up with a good interpretation.


next class: Word Recognition

Visual Illusion Web sites you may find interesting:

Psych 315: Cognitive Psychology Kyle Cave Psychology Dept. U. Mass.