Perceptual Experience

Psy391D - Class 7

(This page last updated 4 October, 2004.)

Perceptual Filling In

• What causes the blind spot?
  • Neurons from retinal ganglion cells all leave the eye at one point.
  • No photoreceptors at that point.
• How do you perceive stimuli that cross the blind spot region?
• Does the visual system actively fill in the blind spot area?
  • "Yes!" says Ramachandran
    • He claims that examples from assignment demonstrate that the visual system fills in simple patterns across the blind spot area before the stimulus is perceived.
    • Can fill in lines across blind spot.
    • Lines that are not aligned may be perceived as aligned.
    • More complex patterns are not reproduced across blind spot.
  • "No!" says Dennett
    • Why should filling-in be necessary? Who would view the filled in stimulus?
    • Once the visual system determines that there is a continuous line that passes through the blind spot, why would it need to draw in the missing portion?
    • Each level of representation is used to build the next level. Once a higher level has been constructed, no need to revise the lower level.
• Patients with scotomas also experience perceptual filling-in.

Next class: Attention and Consciousness

Psych 391D: Consciousness Kyle Cave Psychology Dept. U. Mass.