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Computational Vision

CSCI 363, Fall 2012Lecture 36

Attention and Change Blindness(why you shouldn't text while driving)

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Visual Attention

•Only the region in the center of the retinal image is seen in detail.•Visual attention limits the region of the scene processed.

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Where's Waldo?If we are looking for something in the scene, we must shift our attention around the scene to find it.

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Visual Search Experiments

We can study how people move their attention around using visual search experiments.

•Subjects are asked to look for a target figure among distractors.

•They must respond as quickly as possible saying whether or not the target is present.

•Their reaction time is measured.

•The number of items in the scene is varied.

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Example 1: Find the Blue Square

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Example 1: Find the Blue Square

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Example 2: Find the B

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Example 2: Find the B

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Example 3: Find the O

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Example 4: Find the Orange Square

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Two types of search

Efficient Search: As the number of distractors increases, the reaction time stays the same. (e.g. blue square among red squares).

Inefficient Search: As the number of distractors increases, the reaction time increases.

Reactiontime

Number of items

Efficient

Inefficient

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What this tells us•Inefficient searches show that we are not aware of everything in the entire scene at the same time.

•We constantly shift our gaze and our attention to look at different parts of the scene and examine them in detail.

•We think we see the scene in detail, but we don't.

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Change Blindness during Eye movements

•We are constantly making rapid eye movements, known as saccades, as we scan a scene.

•Vision is suppressed during saccades.

•People fail to notice large changes in the scene if the change occurs during a saccade. (McConkie, Grimes, Ballard and others).

•People also fail to notice large changes in the scene if they occur during a brief disruption (e.g. short blank period).

•This is known as change blindness. (Rensink et al., 1996)

•Demo (view with Firefox): http://www2.psych.ubc.ca/~rensink/flicker/download/

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Movie Cuts can also cause Change Blindness

Can you detect the changes? Conversation MovieOnly 1 in 10 people detected a change.

A cut between scenes can also induce change blindness.

Simons and Levin showed this in a series of experiments.

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Change Blindness for Attended Objects

Change blindness occurs even for objects that are the center of attention:Demo: Person answering phoneOnly 33% of 40 people noticed the main change.

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Change Blindness in Real Life Situations

Disruptions in real life can also lead to change blindness:The door study

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What's Going On?

What causes change blindness?

1) We don't see the entire scene in detail.

2) Only attended regions get into short term memory.

3) Attention is not enough.a) We must intentionally process details in order to detect

the changes.

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Limits of attention

Task: Count the number of passes made by the white team:Counting basketball passes

73% of subjects failed to notice the obvious.This is known as inattentional blindness.

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Cell Phone Use Makes it Worse

Scholl, B. J., Noles, N. S., Pasheva, V., & Sussman, R. (2003) Journal of Vision

Task: Count the number of times a disk crosses the white line.Event: Large item slowly drifts across the field during one of the trials. (Visible for 5 seconds).

Result (no cell phone): 30% fail to notice the cross.

Result (with cell phone): 90% fail to notice the cross.

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Other Effects of Cell phone use

People talking on cell phones while driving...• are more likely to miss traffic signals.• react more slowly to traffic signals when they see them.• don't detect changes in real world traffic scenes as well.• react more slowly to vehicles braking in front of them.

These are all equally true for hands-free devices.

Listening to the radio does not have the same effect.

Sources: Strayer & Johnston (2001) Psychological ScienceStrayer et al. (2003) J. Exp. Psych. Applied

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Don't even think about texting while driving!

Boston Globe, Sunday July 5, 2009Car and Driver conducted a test of texting while driving.

Condition RT (35 mph) RT(70 mph)Sober and attentive 0.51 sec 0.48 secDrunk (BAC .08) 0.55 sec 0.55 secReading a Text 1.00 sec 0.71 secWriting a Text 0.94 sec 0.86 sec

In the texting condition at 70 mph, the car traveled an average of 40 extra feet before the driver hit the brake pedal.

Texting while driving is significantly worse than driving while drunk.

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Thank you for your attention!