Visual attention

Sensation
& Perception
ch 6 1
FARVARDIN NEURO-COGNITIVE TRAINING GROUP

ch 6 2
Sensation & Perception
Visual Attention
Main topics
Binding problem
Feature integration theory
Synchrony hypothesis
The physiology of attention

“neuroenhancing drugs”
 http://www.newyorker.com/reporting/2009/04/27/090
427fa_fact_talbot
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 A young man I’ll call Alex recently graduated
from Harvard. As a history major, Alex wrote
about a dozen papers a semester. He also ran a
student organization, for which he often worked
more than forty hours a week; when he wasn’t
on the job, he had classes. Weeknights were
devoted to all the schoolwork that he couldn’t
finish during the day, and weekend nights were
spent drinking with friends and going to dance
parties. “Trite as it sounds,” he told me, it
seemed important to “maybe appreciate my own
youth.” Since, in essence, this life was
impossible, Alex began taking Adderall to make
it possible.
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Adderall, a stimulant composed of mixed amphetamine
salts, is commonly prescribed for children and adults
who have been given a diagnosis of attention-deficit
hyperactivity disorder. But in recent years Adderall
and Ritalin, another stimulant, have been adopted
as cognitive enhancers: drugs that high-functioning,
overcommitted people take to become higher-
functioning and more overcommitted.
During his college years, Alex took fifteen milligrams of
Adderall most evenings, usually after dinner,
guaranteeing that he would maintain intense focus
while losing “any ability to sleep for
approximately eight to ten hours.”ch 6 5

 Change blindness
 http://viscog.beckman.illinois.edu/flashmovie/11.php
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What is attention for?
 Selecting information
 Enhancing information
 Combining information
What role does attention play in
combining/integrating information?
What physiological mechanism underlie
the integrative process?
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Selecting information
 The retina receives so much information.
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 Attention helps select information.
 This is necessarily because of the way the eye is
structured.
 Most cones reside at the fovea.
 To get accurate information about a scene, we need to select carefully particular
parts of a scene.
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Visual Attention
 Visual attention and eye movement
 Eye tracker
 Eye tracking machine and demo
 http://www.youtube.com/watch?v=lGehsY7pcrc
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Attention also enhances
perception
 If we don’t attend, we lose information.
 If we attend, we understand better.
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Attention helps integrate
information
 Binding problem
 Feature integration theory
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Binding problem
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Two visual pathways (what & where/how
systems)
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Image from Neuroscience, 2nd
Ed. (2000).

Columnar organization
 Neurons that respond to
the same orientation are
packed in the same
column
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Image courtesy of Dr. Paul Wellman and Neuroscience, 2nd
Ed. (2000).

Distributed coding
  Combining input
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Binding problem
 The modular organization of the brain poses an
essential problem.
 How does the brain combine information?
 How does it bind features that are processed
separately?
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 Feature integration theory
 by Treisman & Gelade
Attention plays a central role in
solving the binding problem.
Attention helps organize
information.
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Attention and Figure-ground segregation
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Depending on where you look at, the figure and the ground
switch rapidly.
 Attention plays some role in determining the
figure and the ground.

Attention and 3D structure
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Depending on where to
look at, you get different
kinds of 3D perception.

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Damage to the parietal lobe creates
binding errors.
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Copies of the black (A) and
the white (B) vertical
contour.
Copies of the black (A)
and
the white (B) diagonal
contour.

Feature integration theory
 Attention combines the information from the what and where
systems.
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What can you predict from
this theory?
 If you can’t attend, you can’t combine information.
  Illusionary conjunction
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Demonstration
 I will show you a scene quickly.
 Report first the black numbers.
 Report what you see at each of the 4 locations.
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+++

 Report first the black numbers.
 Report what you saw at each of the 4 locations.
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+++++
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Illusionary conjunctions
 We tend to put different features from different objects together.
 brain damaged patients (parietal lobe) show illusionary conjunctions
even when they view the stimuli for 10 seconds.
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Visual search experiments
 Feature search
 You look for a single feature.
  you don’t need attention
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• Conjunction search
– You need to combine two or
more features (color and
orientation)
  you need attention
• Looking for the target

Visual search experiments
Color Orientation
T: green horizontal
D: green vertical
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• Looking for the target
Color Orientation
T: green horizontal
D1: green vertical
D2: red horizontal

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Find
Which is more difficult?

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Find
Which is more difficult?

Feature binding and attention
(Treisman, 1988)
Experiments:
Task:
Given a stimulus frame containing
visual items, subjects were asked to
indicate whether or not a target
item was present in the frame.
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Feature search vs.
conjunction search
 Feature search
The target item has a unique feature.
 Conjunction search
need to combine features  need
attention.
Because you can attend only one item
at a time, the conjunction search
becomes more difficult when more
items are in the stimulus frame.
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Generality of the results:
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Feature search Conjunction search

Experiments:
 Measure accuracy and response times (conjunction
cases vs. non-conjunction cases)
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Response time
# of
distractors
1000
ms
500ms

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Response
time
# of
distracters
1000
ms
500ms

 Patients with damage to the parietal lobe have
difficulty with conjunction searches.
 (Ambridge et al., 1999)
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Some problems with FIT
 Distinctiveness of features can also create the pop-out phenomenon.
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The physiology of attention
 How do you combine features?
 Synchrony hypothesis
When neurons in different parts of the cortex
are firing to the same object, the pattern of
firing is synchronized (they fire at the same
time, and in the same manner).
So when neurons are firing in synchrony, the
corresponding features are bound together.
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 Separate neurons
respond to color,
contours, textures, so
on.
 Synchrony hypothesis:
 When the features come from the
same object, these neurons fire at
the same time in the same manner.
 This synchronicity of firing binds
features.
 Attention increases
synchronych 6 50

Binding problem and schizophrenia
 People suffering from schizophrenia often experience
hallucination.
 An EEG study shows that brain waves of schizophrenic patients
are not synchronous compared to normal control subjects.
 Spencer, et al (2005). Neural synchrony indexes disordered
perception and cognition in schizophrenia. Proceedings of
National Academy of Sciences, 101, 17288-17293.
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Attention and Autism
 Impaired social interaction and
communication
 Often fail to understand what other people
think.
 Far more autistic boys than autistic girls
(4:1)
 Overrepresented in children whose
parents / grand parents are engineers
 (Baron-Cohen et al.; Autism, 1997, 1, 153-163)
 substantial genetic component
ch 6 52

 Video clip
 Invisible wall
 Autism and symptoms (3:56)
 http://www.youtube.com/watch?v=FuWWie1DlJY
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Attention and Autism
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Eye movement:
normal (white
markers) vs. autistic
viewers (black
markers)

Visual attention

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