Transcript 2320Lecture18.pptx

Upcoming Stuff:
• Finish attention lectures this week
• No class Tuesday next week
– What should you do instead?
• Start memory Thursday next week
– Read Oliver Sacks – The Lost Mariner for Thursday
(26th)
– Read Elizabeth Loftus (For the following week)
Features and Objects in Visual
Processing
The Visual World is an Arrangement of
Features
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Color
Motion
Form
Depth
Orientation
Pre-attentive vs. Attentive Processing
• Pre-attentive processing
– Does the visual system register some basic
features automatically (without attention)
– if so, what features?
– How would you know?
Pre-attentive vs. Attentive Processing
• Indicators of Pre-attentive processing
– 1. processing precedes orienting - if you shift your
attention to something or someplace because of
some processing you did on the information there,
you must have done that processing without
attending
Pre-attentive vs. Attentive Processing
• Indicators of Pre-attentive processing
– 2. processing done in parallel - if you can process
features of several objects simultaneously, you
must have done that processing without attention
Parts vs. Wholes
– We see wholes, but the visual system initially sees
parts (i.e. features) of objects
Parts vs. Wholes
• For example:
We see two rectangles, but the visual pathways initially detects small lines with some
orientation
Parts vs. Wholes
• Simple features form boundaries
We see two rectangles, but the visual pathways initially detects small circles with some
color
Parts vs. Wholes
• Conjunctions don’t form boundaries
We see only one rectangle (at least initially) because the boundaries of the inner one
are made of conjunctions – these require attention to be perceived
“Early parsing of the visual field is
mediated by separate properties,
not by particular combinations of
properties”
What does Treisman conclude from
this observation?
• “Analysis of properties and parts precedes
their synthesis”
• What is the “strong prediction” Treisman
makes?
Illusory Conjunctions
• “errors of synthesis”
Illusory Conjunctions
• Identify the letter on the left of the screen and
the digit on the right
Illusory Conjunctions
Q
4
Illusory Conjunctions
What colored shapes did you see?
Illusory Conjunctions
• Illusory conjunction - when perceived
combination of attributes was not present
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 is thought to require attention focused on
the location of the object to be bound
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
• 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
• Search slope for color singletons is flat. What
does this tell us about color and attention?
Visual Search
• Search slope for shape singletons is flat. What
does this tell us about shape and attention?
Visual Search
• Conjunction search: NOT FLAT!
Visual Search
• Search Slopes can be flat for targets defined by:
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color
orientation
curvature
motion
depth
• What does this imply about these features ?
• What does it tell us about conjunctions of
features ?
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
Feature Integration Theory
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Feature Integration Theory
G
+
N
Feature Integration Theory
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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
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