Experiments for Extra Credit

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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

0200400600800

100012001400160018002000

0 10 20 30 40 50 60Distractors

Response Time (ms)

Visual Search

• Conjunction search: NOT FLAT!

Visual Search

• Serial Search - linear increase in search time with number of distractors

Search Slope

0200400600800

100012001400160018002000

0 10 20 30 40 50 60Distractors

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 ?