lecture4-08 - What is vision used to catch a ball? What can...

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What is vision used to catch a ball? What can we tell from the eye movements?
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Types of Eye Movement Information Gathering Stabilizing Voluntary (attention) Reflexive Saccades vestibular ocular reflex (vor) new location, high velocity, ballistic body movements Smooth pursuit optokinetic nystagmus (okn) object moves, velocity, slow  whole field image motion Vergence change point of fixation in depth slow, disjunctive  (eyes rotate in opposite directions) (all others are conjunctive ) Fixation:  period when eye is relatively stationary between saccades.
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Catching: Gaze Patterns Catcher Thrower saccade X X smooth pursuit X Terminology:  saccadic eye movement
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Catching: Gaze   Anticipation Catcher Thrower X X X 61 ms - 53 ms Timing of departure and arrival linked to critical events Saccade reaction time = 200ms
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What is the significance of prediction? Brain must learn the way ball moves etc and program movement for an expected state of world. Not reacting simply to  current visual information. Stimulus          Response   
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Photoreceptors         ganglion cells        LGN Primary visual cortex        other cortical areas mid-brain         brain stem        muscles Why is prediction necessary? Analysis of visual signals takes a lot of time! Round trip from eye to brain to muscles takes a minumum of 200 msec. Cricket ball only takes about 600 msec. Prediction gets around the problem of sensory delays.  
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20 deg Accuracy of Fixations near Bounce 2D elevation Subjects fixate above the bounce point bounce point How good is prediction?
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YUV420 codec decompressor are needed to see this picture. Poor tracking when ball is unexpectedly bouncy
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lecture4-08 - What is vision used to catch a ball? What can...

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