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 knowledgeInfluence 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?

R

R

R

R

T

R

R

R

R

or

Reddy experiment (continued)

Experiment by Reddy et al. 2. 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)

All letters the same and is circle red or green?

R

R

R

R

T

R

R

R

R

or3. Dual task

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

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.

Neglect Syndrome

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 non-neglected side. These patients may frequently collide with objects or structures such as door frames on the side being neglected.

Raderscheit Self-portraits

2 mo

6 mo

3.5 mo

9 months after right parietal stroke

Neglect