pre-attentive visual processing: what does attention do? what don’t we need it for?
Post on 19-Dec-2015
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Pre-attentive Visual Processing: What does Attention do? What
don’t we need it for?
Parts vs. Wholes
• Simple features form boundaries
Parts vs. Wholes
• Simple features form boundaries
Illusory Conjunctions
Q 4
Visual Search
• Search Slope: How long per item?
Visual Search
• Search Slope: How long per item?
Visual Search
• Serial Search - linear increase in search time with number of distractors
Search Slope
0
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0 10 20 30 40 50 60
Distractors
Response Time (ms)
Visual Search
• Parallel search - search time is independent of distracter number
Search Slope
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 10 20 30 40 50 60
Distractors
Response Time (ms)
Visual Search
• Search Slopes can be flat for targets defined by:– color– orientation– curvature– motion– depth
• What does this imply about these features ?
Visual Search
• But there are some caveats:– What is a search asymmetry?
Search Asymmetry
Search Asymmetry
Search Asymmetry
• But it’s the same discrimination…gaps vs. non-gaps !?
• What model does Treisman propose to explain search asymmetry along with other aspects of visual search?
Feature Integration Theory•Early visual system parses scene into features represented in “feature maps”
•“Attention Spotlight” can be moved across an overlay of these feature maps to bind features together
Feature Integration Theory
• What term does Treisman use to describe the bundle of features at a specific location?
Feature Integration Theory
• Object Files are mental (neural?) representations of the features associated with an object– whenever an object is selected by attention its
features are bound and an object file is opened– when the features of that object change, the
object file is updated
Feature Integration Theory
• How did Treisman et al. test whether the visual system uses object files?
Feature Integration Theory
• Priming: observers are faster to respond to something they’ve just seen
Feature Integration Theory
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Feature Integration Theory
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G
N
Feature Integration Theory
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Feature Integration Theory
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Feature Integration Theory
+G
Feature Integration Theory
What Letter?
Feature Integration Theory
• What was the result?
Feature Integration Theory
• What was the result?– Naming was faster if the prime occurred in the
same box, even though the object had moved
Feature Integration Theory
• What was the result?– Naming was faster if the prime occurred in the
same box, even though the object had moved
• Interpretation?
Feature Integration Theory
• What was the result?– Naming was faster if the prime occurred in the
same box, even though the object had moved
• Interpretation?– visual system establishes object files (e.g. a box
with a G in it) and updates them as the location and features of the object change
The Physiology of Attention
Physiology of Attention
• Neural systems involved in orienting
• Neural correlates of selection
Disorders of Orienting
• Lesions to parietal cortex can produce some strange behavioural consequences
ParietalLobe
Disorders of Orienting
• Lesions to parietal cortex can produce some strange behavioural consequences
– patients fail to notice events on the contralesional side
– Patients behave as if they are blind in the contralesional hemifield
Disorders of Orienting
• Lesions to parietal cortex can produce some strange behavioural consequences
– patients fail to notice events on the contralesional side
– Patients behave as if they are blind in the contralesional hemifield but they are not blind
• Called Hemispatial Neglect
Disorders of Orienting
• Patients will often “neglect” half of their visual field
Disorders of Orienting
• Hypothesis: Parietal cortex somehow involved in orienting attention into contralesional space