Visual search and feature binding

Question 1

What are the two types of visual search?

Answer 1

• Feature search: The target object/stimulus does not share any features with distractors, so ‘pops out’.
• Conjunction search: Target stimulus does share one or more stimulus with distractors, making search more difficult.

Question 2

What does the Feature Integration theory suggest?

Answer 2

That there is a difference in the way we process basic features of an object (which are processed in parallel) and the whole, overall object, which is processed serially and so requires focused attention.

Conjunction searches require serial processing while feature searches only require parallel processing.

Question 3

What does FIT suggest about the stages of visual search?

Answer 3

1. Rapid initial parallel processing to identify features.

2. Slower, serial process to form objects from the combining features.

Question 4

What is parallel processing?

Answer 4

The processing of all objects in an array at once that doesn’t require focused attention.

Question 5

What is serial processing?

Answer 5

Attending to and processing one item in the scene at a time.

Question 6

What are illusory conjunctions?

Answer 6

Occur when features from two different objects are incorrectly combined.

Question 7

When might illusory conjunctions occur?

Answer 7

• When focused attention is absent
• When stored knowledge is absent
• When attention is diverted elsewhere in the display.
• Display/object is in the PPS’ periphery.

Question 8

Prior knowledge can decrease chances of making an illusory conjunction. What does this show about top down influences on feature integration?

Answer 8

Suggests that early stages of feature binding may be subject to top down knowledge.

Question 9

What is the evidence against FIT?

Answer 9

• Rotated letters (Duncan & Humphreys, 1989)

- Negative priming (Tipper, 1985)

Question 10

Describe what Duncan & Humphreys (1989) found against FIT.

Answer 10

Data can be explained in terms of:

• how similar targets are to distractors
• how similar distractors are to each other.

They showed that processing of more than just basic features occurs before attention is applied. (some feature binding occurs rapidly and without attention, which contradicts a basic assumption of FIT.

Question 11

Why does negative priming contradict FIT?

Answer 11

Negative priming tasks show evidence for semantic processing of unattended stimuli. FIT suggests that attention is required for this.

Question 12

What is strength of FIT?

Answer 12

Important contribution to our knowledge on attention.

Question 13

What are two weaknesses of FIT?

Answer 13

• Conjunction searches are faster than predicted.

- The similarity of distractors is influential

Question 14

What did Wolfe’s (1998) Guided Search Theory find about visual search?

Answer 14

We produce an ‘activation map’ in which each item in the display has it’s own level of activation (doesn’t require attention).

Objects with the most activation are attended first.

Suggests initial mix of parallel and serial processing, rather than strictly parallel first and serial second.

Question 15

What condition might you have if you have deficits in feature binding?

Answer 15

Balint’s Syndrome

Question 16

What is Balint’s Syndrome?

Answer 16

A condition that causes:

• optic ataxia (unable to reach objects held out by experimenter)
• simultagnosia (unable to focus attention on more than one object at a time)
• oculomotor apraxia (inability to voluntarily control the eyes)

Is caused by damage to parietal lobe damage.

Question 17

Treisman (1999) studied a patient (RM) who had large areas of damage in the occipito-parietal cortex. What symptoms did he show?

Answer 17

• Simultagnosia

- Had difficulties with combining features of a stimulus. (made many conjunction errors, even after 10 seconds)

Question 18

Which region, other than the parietal lobe, is associated with impairments in feature binding?

Answer 18

Thalamas

Question 19

What did Corbetta et al (1995) find about where feature binding might be based?

Answer 19

Increased activation in the posterior temporal cortex and parietal cortex during conjunction searches.

Question 20

Shafritz et al. (2002) investigated the claim that the parietal lobe is just involved in more difficult attention tasks. What did they find?

Answer 20

The claim was wrong - parietal areas are more active during conjunction search than during feature searches. They varied task difficulty with different conditions of what PPS had to attend to - as well as the number of different features they were instructed to attend to.

Question 21

What did Walsh et al’s (1995) TMS study find about the parietal lobe?

Answer 21

Used TMS to stimulate the parietal lobe and then tested reaction times on conjunction and feature searches.

Found a disruption in RTs for conjunction but not feature searches.

Question 22

What did Esterman et al (2007) find out about TMS and illusory conjunctions?

Answer 22

They used TMS to stimulate the intraparietal sulcus and found that the number of illusory conjunctions decreased when doing so.