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Experiments for Extra Credit
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• Read article by Anne Treisman
Information Theory
• Donald Broadbent - earliest systematic investigations of selective attention
•First principle of human information processing: capacity is limited
Information Theory
• Donald Broadbent - earliest systematic investigations of selective attention
Second principle of human information processing: information sources can be selected
Shadowing
• Many early studies employed variations on a paradigm called “shadowing”
“Four score and seven years ago…”
“It was the best of times, it was the worst of times…”
“Four score and seven years ago…”
Stages of Selection
• Broadbent: Early Selection - a bottleneck exists early in the course of sensory processing that filters out all but the attended channel
• Alternative theory: Late Selection - the bottleneck exists not at the lowest stages, but at the highest - such as response planning, memory and consciousness
Stages of Selection
Stages of Selection
• Testing Early Selection Theory - what prediction can be made?
Stages of Selection
• Testing Early Selection Theory - what prediction can be made?
• Information (such as words) in unattended channel shouldn’t be processed for meaning
Stages of Selection
• Testing Early Selection Theory - what prediction can be made?
• Information (such as words) in unattended channel shouldn’t be processed for meaning
• Demonstrates that Early Selection Theory is not entirely correct
Stages of Selection
• Testing Early Selection Theory - what is another prediction that can be made?
Stages of Selection
• Testing Early Selection Theory - what is another prediction that can be made?
• Should be able to find differences in brain activity in primary sensory areas (A1, V1)
Stages of Selection
• Electrical activity recorded at scalp (EEG) shows differences between attended and unattended stimuli in A1 within 90 ms
Hansen & Hillyard (1980)
Stages of Selection
• Evidence exists for both early and late selection mechanisms
– One interpretation: early reduction in “sensory gain” followed by late suppression of unselected information
Capacity Limitations in Vision
• A limit on the amount of information you can process at once shows up in visual perception
• “Cluttered” or dense scenes
• Visual Search: finding a single item in a cluttered visual scene
Visual Search
• Visual Search: finding a single item in a cluttered visual scene
Visual Search
• Is there a green square?
Visual Search
• Is there a green square?
Visual Search
• Parallel search: like many independent spotlights
Visual Search
• Serial search: each item is selected until target is found
Visual Search
• Serial search: each item is selected until target is found
Visual Search
• Serial search: each item is selected until target is found
Visual Search
• Serial search: each item is selected until target is found
Visual Search
• How could you test which kind of search was happening?
Visual Search
• Search Slope: How long per item?
Visual Search
• Search Slope: How long per item?
Visual Search
• Search Slope: How long per item?
Visual Search
• Parallel search - search time is independent of distracter number
Search Slope
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Distractors
Response Time (ms)
Visual Search
• Conjunction search: NOT FLAT!
Visual Search
• Serial Search - linear increase in search time with number of distractors
Search Slope
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Distractors
Response Time (ms)
Visual Search
• Search slope for shape singletons is flat. What does this tell us about shape and attention?
Visual Search
• Search slope for color singletons is flat. What does this tell us about color and attention?
Visual Search
• Search Slopes can be flat for targets defined by:– color– orientation– curvature– motion– depth
• What does this imply about these features ?• What does it tell us about conjunctions of features ?
