Transcript Visual Attention

Chapter 6:
Visual Attention
Taking a dip at the mall
 http://gawker.com/5733870/girl-falls-into-mall-fountain-while-
texting
Watch out for colliding texters
 Many pedestrians are so distracted by texting that they will
step into the path of an oncoming vehicle while crossing
the street; even when walkers have the right of way,
inattentiveness can be a factor in pedestrian crosswalk
accidents. Texters can collide with street signs and similar
objects, bicyclists or even other pedestrians. And, the
potential for falls is enormous (there have been recorded
instances of pedestrians disappearing into open manholes
while perusing their mobile devices).
 Source: sdinjury.com
Texters make good targets
 California police officers have even recorded a significant
uptick in crime aimed at text-messaging pedestrians: not
only does a nice cell phone present a tempting target for a
mugger, walkers who are texting are not paying attention to
their surroundings. Thieves have found that victims who are
texting are easier to surprise and have a harder time
identifying perpetrators in police lineups.
 Source: personal injury law firm (sdinjury.com)
Attention and Perceiving the Environment
 Divided attention - paying attention to more
than one thing at one time
 Driving a car- have to pay attention to many
things.

This ability is limited, which has an impact on how much
we can process at once

Shifting attention between impt stimuli
 Selective attention - focusing on specific
objects and filtering out others
Why is Selective Attention Necessary?
 Some aspects of the environment are more
important and interesting than others.
 The visual system has evolved to operate in
this fashion

There is too much incoming stimulation at the retina to
process everything.

Selection is achieved partially through use of the fovea.
How is Selective Attention Achieved?
 Scanning a scene - eye movements can take in
different parts of a scene

Measuring eye movements - camera-based eye trackers
show:
Saccades
- small, rapid eye movements
Fixations - pauses in eye movements that
indicate where a person is attending
Approximately three fixations per second
Figure 6.3 A person looking at a stimulus picture in a
camera-based eye tracker.
Location of Fixations
 Characteristics of the scene:

Stimulus salience – (what stands out) 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.
Characteristics of the Scene
 Picture meaning and observer knowledge

Scene schema - prior knowledge about what is found in
typical scenes
Fixations
are influenced by this knowledge
 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.
Figure 6.6 Sequence of fixations of a person making a
peanut butter sandwich.
Effects of Past Experience
 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.
Perception without Focused Attention
 Experiment by Reddy et al.

Observers performed one of three tasks
1.
Central task - determine whether letters
flashed in the center of the screen are the
same

A face or a circle is presented in periphery but not part of
the task
All letters the same?
RRR
R RR
R T R
or
Reddy experiment (continued)
 Experiment by Reddy et al.
Peripheral task – Subject asked to look
at letters but not part of task. Instead must
determine whether faces flashed to the
side of the screen are male or female (of
disc is red or green)
3. Dual task – asked to both tasks.
Tell if letters are the same (central task)
and do the peripheral task as well
(male/female or red/green)
2.
All letters the same and is circle red or green?
RRR
R RR
R T R
3. Dual task
or
Experiment by Reddy: Conclusion
 Performance on central and perihperal
conditions was 80 to 90%.
 Performance in the dual task condition was
90% for faces, and 54% for the discs.
 Results show that the gender of a face can be
determined without focused attention while
the disc identification could not be made.
 Faces have meaning and are perceived as
whole objects.
Inattentional blindness
 Inattentional blindness - a stimulus is not
perceived even when the person is looking
directly at it.
http://theinvisiblegorilla.com/gorilla_experiment.html
Inattentional blindness
 Invisible Gorilla

Experiment by Simons and Chabris
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.
Change Blindness
 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.
VL6 5-11
When Is Attention Necessary for Perception? continued
 Change blindness also occurs for film shots.
 http://www.youtube.com/watch?v=owH54AiCheg
 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.
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
Experiment by Klin et al. - continued
 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 6.27 Where people look when viewing this image from the film Whose Afraid of Virginia Woolf?
Nonautisitic viewers: white crosses; autistic viewers: black crosses. From “The Enactive Mind, or From
Actions to Cognition: Lessons from Autism,” by A. Klin, W. Jones, R. Schultz, & F. Wolkmar, Philosophical
Transactions of the Royal Society of London B, pp. 345-360. Copyright 2003. The Royal Society. Published
online.
Figure 6.28 Scan paths for nonautistic viewers (white
path) and autistic viewers (black path) in response to the
picture and dialogue while viewing this shot from Whose
Afraid of Virginia Woolf
Neglect Syndrome
 unilateral visual inattention is a
neuropsychological condition in which, after damage
to right parietal lobe of the brain is sustained, a
deficit in attention to and awareness of the left side
of space is observed. It is defined by the inability of a
person to process and perceive stimuli on left side of
the body or environment that is not due to a lack of
sensation.
Question: What’s in this picture?
Response: A cat.
Neglect 2
 For example, a stroke affecting the right parietal lobe
of the brain can lead to neglect for the left side of the
visual field, causing a patient with neglect to behave
as if the left side of sensory space is nonexistent.
Neglect 3
 In an extreme case, a patient with
neglect might fail to eat the food on
the left half of their plate, even
though they complain of being
hungry.
 If someone with neglect is asked to
draw a clock, their drawing might
show only numbers 12 to 6, or all 12
numbers on one half of the clock
face, the other side being distorted or
left blank.
Neglect 4
 Neglect patients may also ignore the left side of their
body, shaving or adding make-up only to the nonneglected side. These patients may frequently collide
with objects or structures such as door frames on the
side being neglected.
Raderscheit Self-portraits
Neglect
2 mo
6 mo
3.5 mo
9 months
after
right
parietal
stroke