Experiments for Extra Credit
• Still available
• Go to www.tatalab.ca to sign up
Next Tuesday
• 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…”
“Four score
and seven
years
ago…”
“It was the
best of
times, it was
the worst of
times…”
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
2000
Response Time (ms)
1800
1600
1400
1200
1000
800
600
400
200
0
0
10
20
30
Distractors
40
50
60
Visual Search
• Conjunction search: NOT FLAT!
Visual Search
• Serial Search - linear increase in search time with
number of distractors
Search Slope
2000
Response Time (ms)
1800
1600
1400
1200
1000
800
600
400
200
0
0
10
20
30
Distractors
40
50
60
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 ?