Section_4_Notes

Section_4_Notes - Cognitive Neuroscience Section 4...

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Cognitive Neuroscience Section 4 Perceptual categorization Perception, attention, and memory are all interrelated. From the perspective of memory, perception is seen as the updating of memory by new sensory experience. Perception involves sensory analysis within the framework of previous experience as stored in memory. The perceptual categorization of sensory input is guided by previously established memory. For perception to be guided implies that it is an active, not a passive, process. But this implication is not universally accepted. For the case of vision, we will consider whether it is more appropriate to view perception as being passive or active.
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The argument for passive visual perception: 1) The visual stimulus operates like a stamp or imprint. 2) All the information needed for visual perception is presented to the retina from the external world. 3) Visual perception depends only on feedforward processes. 4) Low-level visual features are detected in V1, and progressively more elaborate features are detected in higher visual areas. 5) Visual recognition occurs when high-level symbolic features are compared with features stored in memory. Evidence for this view: a) The topographic projection of the retina to V1 and higher visual areas suggests a faithful reproduction of light patterns impinging on the retina. b) Lesions along path from retina to V1 produce blindness for the part of the visual field corresponding to the lesioned cells. c) Lesions in visual areas outside of V1 produce "mind-blindness" -- lack of visual comprehension.
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The argument for active visual perception: 1) The visual stimulus is highly variable and indeterminate. 2) Much of the information needed for perception is supplied by the brain. 3) Visual perception depends on feedback as well as feedforward processes. 4) Low-level activity patterns in V1 undergo progressive elaboration through an iterative feedforward-feedback cycle involving higher visual areas. 5) Visual recognition occurs when high-level visual areas produce patterns from memory representing hypotheses that are consistent with low-level activity patterns. Evidence for this view: a) Because the visual sensorium is constantly changing, retinal activity does not specify what constitutes a light pattern to be perceived. b) Top-down inputs to V1 are more prevalent than bottom-up inputs. c) Visual perception can occur with visual input, as in imagery .
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The Adaptive Resonance Theory (ART) of Grossberg is a class of models that captures some of the cardinal features of active visual perception.
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The ART search cycle : 1. an input pattern I registers itself as a short-term memory activity pattern x in area F1 (frame a) 2. Pattern x is transformed into a compressed pattern T in area F2 (frame a) 3. Competition occurs among nodes in F2 for the strongest match with T (frame a) 4. Activation of memory trace y occurs at the node in F2 having the strongest match (frame a) 5. Memory trace y is treated as a hypothesis to be tested by matching its top-
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Section_4_Notes - Cognitive Neuroscience Section 4...

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