Download 2320Lecture19 - U of L Class Index

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Visual Search: finding a single item in a cluttered visual scene
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
• Parallel search: like many independent spotlights
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
• 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
• Conjunction search: NOT FLAT!
Illusory Conjunctions
Q
4
Illusory Conjunctions
• Illusory conjunction - when perceived combination of
attributes was not present
• Supports notion that primitive features are processed
independently and then bound together to form
objects
• This binding process is thought to require attention
focused on the location of the object to be bound
Treisman’s 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
•Focused attention is
required to “bind”
features together into
objects
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
• Prediction: if visual system is “object oriented” then
priming effect should be attached to objects even
when they move around
Feature Integration Theory
+
Feature Integration Theory
G
+
N
Feature Integration Theory
+
Feature Integration Theory
+
Feature Integration Theory
G
+
Feature Integration Theory
What Letter?
Feature Integration Theory
• Compare “primed” box with “unprimed” box. 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
– Priming isn’t locked to the location of the prime itself
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
– It is faster to make small changes than large changes
Attention and Consciousness
• Sensory information must be attended for it to be
entered into awareness
Attention and Consciousness
• We’ve seen how orienting and selection interact to
enable enhanced perception
• Enhanced perception includes awareness
• Thus attentional selection is the gateway to
consciousness
Attention and Consciousness
• The attention orienting mechanism can be confused
leading to something called “change blindness”
Attention and Consciousness
• Change blindness
– Change blindness shows us that the feeling of being in a
detailed visual environment is really just an illusion
– We only have access to the parts of the scene to which we
have attended
Attention and Consciousness
• Change blindness
– Change blindness shows us that the feeling of being in a
detailed visual environment is really just an illusion
– We only have access to the parts of the scene to which we
have attended
– And that is often not very much!