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class+12+lecture_posted (1) - Sensation and Perception...

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Sensation and Perception Class XI: Space & Motion Perception
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Computation of Visual Motion How would you build a motion detector? Motion is just a change in position over time Start with two adjacent receptors § Registers change in position Incorporate a delay § Accounts for change in time
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Figure 7.3 Constructing a neural circuit for the detection of rightward motion (Part 1)
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Figure 7.3 Constructing a neural circuit for the detection of rightward motion (Part 2)
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Notes about this circuit: It’s directional… why ? It’s velocity-dependent… why ? It could work for edges if the inputs are spatially filtered.
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Computation of Visual Motion Apparent motion : The (illusory) impression of smooth motion resulting from the rapid alternation of objects appearing in different locations in rapid succession First demonstrated by Sigmund Exner in 1875 Motion detector circuit does not need real motion in order to fire Simply switching position at the right speed will produce the illusion of continuous motion This is the basis of ANIMATION…but That’s Not All, Folks!
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Computation of Visual Motion Aperture : An opening that allows only a partial view of an object Correspondence problem (motion): The problem faced by the motion detection system of knowing which feature in frame 2 corresponds to a particular feature in frame 1 Aperture problem : The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of the object may be ambiguous
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Figure 7.5 Movies illustrating the aperture and correspondence problems
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Figure 7.6 Building a global-motion detector
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Computation of Visual Motion We can say something about where global-motion detectors are: Lesions in magnocellular layers of LGN impair perception of large, rapidly moving objects Middle temporal lobe (Area MT) a brain region that plays an important role in motion perception. § The vast majority of neurons in MT are selective for motion in a particular direction
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Figure 7.7 The middle temporal lobe and other regions of the cortex involved in motion perception
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Computation of Visual Motion Newsome and Pare (1988) conducted a study on motion perception in monkeys Trained monkeys to respond to correlated dot motion displays The MT area of the monkeys was lesioned Result: Monkeys needed about ten times as many dots to correctly identify direction of motion
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Figure 7.8 The Newsome and Pare paradigm
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Computation of Visual Motion Disadvantages of using lesion studies to study motion: Invasive Lesions may be incomplete or may influence other
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class+12+lecture_posted (1) - Sensation and Perception...

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