PSYB51H3 Chapter Notes - Chapter 7: Motion Perception

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12 May 2011
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Chapter 7: Motion Perception
We need something that quickly detects motion for survival
Motion After Effect (MAE): After seeing a moving object for 15+ seconds, we see
still objects as moving in the opposite direction
MAE is caused by opponent process for motion detection
oLike how colour after effect is caused color opponent process
Computation of Visual Motion
Simple motion detector Fig. 7.3c
oD delays transmission and stops firing if light stays on A
oX is multiplication cell, fires only when B&D are active
oHuman motion detection is elaboration of this
oM wont respond to large bug b/c it is in both receptive fields
oOnly works for one direction
oToo fast/slow causes B&D to be out of sync
oMore realistic is w/ more detectors joined
Apparent Motion
If an object appears in As RF disappears, then re-appears in Bs RF It will be
detected as motion
Apparent Motion: illusion of motion from fast changes in position of objects
oe.g. Cartoons
The Correspondence and Aperture Problems
Aperture: Opening that allows partial view of object
If limit our view of something, it inhibits our ability to detect correct motion
oAperture problem: When moving object is seen through aperture, perceived
direction of motion may differ from if we saw the whole object
Correspondence Problem (motion): Motion detection system doesnt know which
feature in 2nd frame belongs to 1st frame
oe.g. Fig 7.5
Each neuron in V1 (primary visual cortex) has limited RF, so is like aperture
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A separate set of neurons listen to the V1 cells to figure out which direction is the
most agreed upon. (This is the direction we perceive)
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