chapter6

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Chapter 6:
Visual Attention
Scanning a Scene
• Visual scanning – looking from place to place
– Fixation
– Saccadic eye movement
• Overt attention involves looking directly at the
attended object
• Covert attention is attention without looking
Figure 6-1 p128
Figure 6-2 p129
Figure 6-3 p129
What Directs Our Attention?
• Characteristics of the scene:
– Stimulus salience - areas of stimuli that
attract attention due to their properties
• Color, contrast, and orientation are
relevant properties.
• Saliency maps show fixations are
related to such properties in the initial
scanning process.
Figure 6-4 p130
Figure 6-5 p131
Selection Based on Cognitive Factors
• Picture meaning and observer knowledge
– Scene schema - prior knowledge about
what is found in typical scenes
• Fixations are influenced by this
knowledge
Selection Based on Cognitive
Factors - continued
• Experiment by Shinoda et al.
– Observers’ fixations were measured
during computer simulated driving.
– They were more likely to detect stop signs
when they were at intersections.
– People have learned that this is where stop
signs are typically placed.
Figure 6-6 p131
Task Demands
• Influence of the observer’s task
– Task demands override stimulus saliency.
– Eye movements and fixations are closely
linked to the action the person is about to
take.
– Dynamic environment experiment,
Jovancevic-Misic and Hayhoe (2009)
Figure 6-7 p132
What Happens When We Attend?
• Attention to specific locations is called spatial
attention
• Experiment by Posner (1978) et al.
– Observers looked at a fixation point.
– Precueing with an arrow indicated on
which side a stimulus was likely to appear.
– Stimuli appeared that were consistent
(valid trial) or inconsistent (invalid trial) with
the cue.
– Task was to push button when a target
square was seen.
What Happens When We Attend? continued
• Results showed that observers responded
fastest on valid trials.
• Posner believed these results showed that
information processing is most efficient where
attention is directed.
Figure 6-8 p133
Figure 6-9 p133
What Happens When We Attend? continued
• Experiment by Egly et al.
– Observer views two rectangles.
– Cue signals where target may appear.
– Task was to press button when target
appeared.
– Results show:
• Fastest reaction time at targeted position
• “Enhancement” effect for non-target
within the target rectangle
Figure 6-10 p134
Figure 6-11 p134
Attention Can Influence Appearance
• Experiment by Carrasco et al.
– Observers saw two grating stimuli with
either similar or different contrast between
the bars.
– Task was to fixate on center point between
gratings and indicate orientation of bars
with higher contrast.
– Small dot was flashed very quickly on one
side before gratings appeared.
Attention Can Influence Appearance. continued
• Experiment by Carrasco et al.
• Results showed that:
– when there was a large difference in
contrast, the dot had no effect.
– when the contrast was the same,
observers were more likely to report that
the grating preceded by the dot had higher
contrast.
– Thus the shift of attention led to an effect
on perception
Figure 6-12 p135
Attention Can Influence Physiological
Responding
• O’Craven (1999) – Subject attended to the
house or face show that attending to the
moving or stationary face caused enhanced
activity in the FFA and attending to the
moving or stationary house caused enhanced
activity in the PPA
Figure 6-13 p135
Attention Can Influence Physiological
Responding - continued
• Datta and DeYoe (2009)
– Attention maps show directing attention to
a specific area of space activates a specific
area of the brain.
• Womelsdorf (2006) – showed that attention
can cause a monkey’s receptive field to shift
toward the place where the attention is
directed.
Figure 6-14 p136
Figure 6-15 p137
What Happened When We Don’t Attend?
• Inattentional blindness - a stimulus is not
perceived even when the person is looking
directly at it
– Experiment by Simons and Chabris (1999)
• Observers are shown short film of teams
passing a basketball.
• Task is to count number of passes.
• Either a woman with an umbrella or a
person in gorilla suit walks through the
teams.
• 46% of observers fail to report the
woman or gorilla.
Figure 6-16 p138
Figure 6-17 p138
Change Detection
• Change blindness
– Observers were shown a picture with and
without a missing element in an alternating
fashion with a blank screen.
– Results showed that the pictures had to
alternate a number of times before the
change was detected.
– When a cue is added to show where to
attend, observers noticed change more
quickly.
Change Detection - continued
• Change blindness also occurs for film shots.
• People are “blind” to the fact that they
experience change blindness.
• Real objects in the environment change with
some type of movement, which is why we
normally don’t experience change blindness.
Video: Change Blindness
Figure 6-18 p139
Figure 6-19 p139
IS Attention Necessary for Perceiving
Scenes?
• Experiment by Li et al (2002)
– Observers performed one of three tasks
• Central task - determine whether letters
flashed in the center of the screen are
the same
• Peripheral task - determine whether
faces flashed to the side of the screen
are male or female
• Dual task - do the same as the
peripheral task and determine the color
of a disc
Figure 6-20 p140
Figure 6-21 p140
The Distracting Effects of TaskIrrelevant Stimuli
• Task-irrelevant stimuli are stimuli that do not
provide information relevant to the task
• Foster and Lavie (2008)
– Load theory of attention
– Perceptual capacity
– Perceptual load
– Low-load tasks
Figure 6-22 p141
Figure 6-23 p142
Attention and Experiencing a Coherent
World
• Binding - process by which features are
combined to create perception of coherent
objects
• Binding problem - features of objects are
processed separately in different areas of the
brain
• So, how does binding occur?
Figure 6-24 p142
Feature Integration Theory
– Preattentive stage - features of objects are
separated
– Focused attention stage - features are
bound into a coherent perception
Figure 6-25 p143
Feature Integration Theory - continued
• Illusory Conjunctions - features that should be
associated with an object become incorrectly
associated with another.
• Experiment by Triesman & Schmidt
– Stimulus was four shapes flanked by two
numbers.
– Display flashed briefly, followed by a mask.
– Task was to report numbers first followed
by shapes at four locations.
Figure 6-26 p143
Figure 6-27 p144
Feature Integration Theory - continued
• Triesman & Schmidt results showed that:
– incorrect associations of features with
objects occurred 18% of the time.
– asking observers to focus on the target
objects eliminated this effect.
• Balint’s syndrome - patients with parietal
lobe damage show lack of focused attention
results in incorrect combinations of features
Figure 6-28 p144
Visual Search
• Conjunction search - finding target with two or
more features
– Patients with parietal lobe damage cannot
perform conjunction searches well
compared to people without such damage.
– Parietal lobe is the destination for the
where stream.
Figure 6-29 p145
Attention and Autism
• A major symptom of autism is withdrawal from
contact with people.
• People with autism can solve reasoning
problems about social situations, but cannot
function when placed in these situations.
• Experiment by Klin et al.
– Participants were autistic and nonautistic
people.
– Watched movie while eye fixations were
tracked
Attention and Autism - continued
• Experiment by Klin et al. results for nonautistic
observers showed:
• Looked at eyes of actors to determine
emotional state
• Looked in the direction a person pointed
and then at the face of the person who
should reply
• Autistic observers look at socially irrelevant
stimuli in these situations.
• Thus, where autistic individuals pay attention in
a social situation may lead to perceiving the
world differently.
Figure 6-30 p145
Figure 6-31 p146
Attention and Autism - continued
• Experiment by Pelphrey et al.
– Measured responses in the STS
– Nonautistic and autistic participants
watched an animated character that:
• moved eyes toward a checkerboard
(congruent condition).
• moved eyes away from a checkerboard
(incongruent condition).
Attention and Autism - continued
• Observers pressed a button when they saw
the character’s eyes move.
– All participants performed at 99% accuracy.
– But, activation of the STS for nonautistic
people was higher in the incongruent
condition.
– Autistic people showed equal activation in
both conditions.
• Results suggest that autistic people cannot
read intentions of others.
Figure 6-32 p146
Attention and Perceptual Completion
• Perceptual completion is the perception of an
object as extending behind occluding objects
• Habituation – one stimuli is presented to an
infant repeatedly and the infant’s looking
time is measures
– Dishabituation is an increase in looking time when
a stimulus is changed
Figure 6-33 p147
Figure 6-34 p148
Figure 6-35 p148
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