Visual attention

What is attention?

the ability to process some parts of a stimulus at the expense of others

Why is attention needed?

the perceptual system has a limited capacity

What is the difference between overt and covert attention?

Overt= looking directly at an object

Covert = looking at one object but attending to another

What is a fixation?

When a person is looking at an object

What is a saccade

A rapid movement of the eye between fixation points

What directs our attention?

Initial involuntary process (mediated by attentional capture), followed by a voluntary process (guided by your goals and expectations)

What is attentional capture determined by?

the salience (noticeability) of an image

What captures our attention?

Contrast

- colour/luminance

- size

- orientation

- motion/flicker

Fixations are not only determined by goals...

they are also determined by expectations, if an object is unexpected, you will fixate on it

What are the effects of attention?

speed of responses (posner), can influence appearance (carrasco), can influence physiological responding (neurons in the brain respond stronger to attended stimuli)

what is the binding problem?

the issue of how an object's individual features are bound to create a coherent percept

why is the binding problem an issue?

different aspects of a stimulus are processed independently, often in separate brain areas

Feature integration theory (FIT)

the theory that the binding problem is solved by attending to only one location at a time

Illusory conjunctions

A prediction of FIT - if attention is inhibited, features from different objects will be incorrectly bound together

What did Treisman and Schmidt show?

That illusory conjunctions occur, Character strings were presented briefly followed by noise mask, Observers had to report the numbers and letters, often associating the wrong colour with the wrong letter or number

Balint's syndrome

A condition caused by damage to the parietal lobe, Involves difficulty focusing attention on a single object, prone to illusory conjunctions

What do conjunction searches require?

Binding and are predicted to be slow

What do feature searches require?

do not require binding and are predicted to be fast

What is change blindness?

failing to notice changes in the environment

Why doesn't change blindness occur all the time?

Because changes usually generate motion transients that draw attention to the location change, thereby making it easy to spot the change.

When and who showed that attention can make objects appear to have a higher contrast?

Carrasco et al. in 2004

When and who showed that attention can impact speed responses?

Posner in 1978

What is a conjunction search?

If a target differs from distractors by its particular conjunction of features

What is a visual search?

If a target differs from distractors by one feature that the distractors do not have

What does FIT predict?

That if attention is inhibited, features from different objects will be incorrectly bound together