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Chapter 7

Chapter 7 - Study notes

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University of Toronto Scarborough
Matthias Niemeier

CHAPTER 7: MOTION PERCEPTION COMPUTATION OF VISUAL MOTION -motion is a low level perceptual phenomenon. Many cells in V1 selectively respond to motion in one particular direction Motion aftereffect (MAE) = illusion of motion of a stationary object that occurs after prolonged exposure to a moving object. Similar to color aftereffect, just as it is caused by opponent processes for color vision. MAE is caused by opponent processes for motion detection. If fixate on falling object then watch stationary object that object seems to be moving up Motion = change in distance over time. To build a motion detector start with 2 adjacent receptors pt A and B, neuron A and B, separated by a fixed distance. A bug moving from left to right would first pass through neuron As receptive field then a short time later would enter receptor Bs receptive field. Thus a 3 cell (M-motion detection cell) that listens to neurons A and B should be able to detect this movement M cant just add up excitatory inputs form A and B. M would fire in response to the moving bug, but it would also respond to a large stationary bug that covered both receptive fields. Thus we have 2 additional components in neural circuit. First new cell = D receives input form A and delays transmission of this input for a short period of time. D also has a first adaptation rate, it fires when cell A initially detects light, but quickly stops firing if the light remains shining on As receptive field. B and D are then connected to neuronX, a multiplication cell. This multiplication cell will fire only when both cells B and D are active. By delaying receptors As response (D) and then multiplying it by receptor Bs response X, we can create a mechanism that is sensitive to motion. This mechanism would be direction- selective. It respond well to motion from left to right but not from right to left. This mechanism also tuned to velocity cuz when bug is moving at just right speed (if bug moves to fast it not work), delayed response from receptor A and direct response from receptor B occur at the same time and thus reinforce each other AND gate cell X fires if and only if BOTH itz inputs (B and D) are firing simultaneously, and it passes this message on to the motion detection cell M. This concept is not correct. A better concept is based on linear filters that delay, sum and then are followed by nonlinearities APPARENT MOTION Neural circuit not require continuous motion in order to fire. Apparent motion = illusory, impression of smooth motion resulting from the rapid alternation of objects that appear in www.notesolution.com
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