read this article for next week: a neural basis for visual search in inferior temporal cortex...
TRANSCRIPT
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Read this article for next week:
A Neural Basis for Visual Search in Inferior Temporal Cortex
Leonardo Chelazzi et al. (1993) Nature
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How are you doing on your projects?
By now you should have sorted out:The theory is that:
The prediction is that:
The best technique to test the prediction is:
oThe experimental would work like this:
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Attention Orienting System and Associated Disorders
Neglect, Extinction and Balint’s Syndrome
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What system orients attention through space
• Attention is sometimes compared to a “mental spotlight”
• What system(s) control the spotlight?
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What system orients attention through space
• Corbetta et al. (1993)
– Subjects oriented attention according to a light moving in the visual field
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Orienting Spatial Attention
• Results:
– Parietal and Pre-motor areas were activated by attention tracking task
– Hemisphere of activation depended somewhat on which visual field attention was being shifted in
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Orienting Attention
• Posner Cue - Target Paradigm:
Subject presses a button as soon as x appears
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
X
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
That was a validly cued trial because the x appeared in the box that flashed
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
X
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Orienting Attention
• Posner Cue - Target Paradigm:
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Orienting Attention
• Posner Cue - Target Paradigm:
That was an invalidly cued trial because the x appeared in the box that didn’t flash
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Paradigms Used To Study Attention
• Posner Cue - Target Paradigm:
Attention Effect = Valid RT - Invalid RT
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Orienting Spatial Attention
• Corbetta et al (1993) confounded stimulus w/ orienting
• Hopfinger et al. (2000) used event-related fMRI to identify top-down orienting processes (distinct from stimulus-driven processes)– Cue-target paradigm using
arrows
– What is the brain activity caused by the cue?
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Orienting Spatial Attention• Result:
– Cue-related activations indicate a distributed network that mediates voluntary orienting
– Network includes mainly frontal and parietal structures, mainly on the left side (keep this in mind for discussing neglect)
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Hemispatial Neglect
• Unilateral lesion to Parietal or Temporo-Parietal Junction
• Patients present with vision problems, but are not “blind”– Rather, they fail to
apprehend (and interact appropriately with) stimuli in the contralesional field
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Hemispatial Neglect• E.g. line bisection
task
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Hemispatial Neglect• E.g. reproducing visual forms
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Investigation of Neglect with Cue-Target Paradigm
• Posner et al. (late 1970s) used a cue-target paradigm
• Parietal Lobe patients are profoundly impaired only when invalidly cued to attend to the ipsilesional (good) side
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Attention as Information Selection
– Visual search
– auditory “Cocktail Party” problem
– somatosensory “I don’t feel my socks” problem
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Early Selection
• Early Selection model postulated that attention acted as a strict gate at the lowest levels of sensory processing
• Based on concept of a limited capacity bottleneck
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Late Selection
• Late Selection models postulated that attention acted on later processing stages (not sensory)
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Late vs. Early
• Various hybrid models have been proposed– Early attenuation of non-attended input
– Late enhancement of attended input
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Electrophysiological Investigations of Attention
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Modulation of Auditory Pathways• Hillyard et al. (1960s)
showed attention effects in human auditory pathway using ERP
• Selective listening task using headphones
– Every few minutes the attended side was reversed
– Thus they could measure the brain response to identical stimuli when attended or unattended
beep beep beep beep boop beep
beep beep beep boop beep beep
attending LEFTIgnoring RIGHT
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Modulation of Auditory Pathways
• Result: ERP elicited by attended and unattended stimuli diverges by about 90ms post stimulus– Long before response is made
– Probably in primary or nearby auditory cortex