Visual Search

Question 1

Give 4 examples of real world visual search

Answer 1

Scanning airport baggage, searching for tumours in body scans, searching for prey or food in the forest, searching for food on the supermarket shelves

Question 2

What makes baggage search different to searches in the lab?

Answer 2

In the airport your don’t know exactly what you’re looking for

Question 3

How do we keep visual search operators alert?

Answer 3

By including false targets now and again

Question 4

What were Treisman & Gelade’s (1980) main findings re: visual search for features vs. conjunctions & the presence vs. absence of stimuli?

Answer 4

1) Feature search RTs were unaffected by display size
2) Conjunction search RTs were affected by display size
3) Finding stimuli took 2x as long as concluding stimuli were not present because the former can usually end by the time that 1/2 of stimuli have been checked

Question 5

The premise of FIT theory is that….

Answer 5

Selective attention and so serial processing is required to integrate features. Otherwise, inattentive, parallel processing can perform the job of detection

Question 6

What sort of maps can be found in FIT theory?

Answer 6

Feature maps e.g. colour or orientation maps which specify the presence of these features. Master maps of space which bind together features present at a particular location

Question 7

In terms of searching for the presence vs. absence of a feature e.g. Qs vs. Os, FIT fails to convincingly explain why…

Answer 7

Searching for an O amongst Qs takes longer than searching for the presence of a feature I.e. the line across the O I.e. a Q

Question 8

Name 3 ways in which feature may be bound to form objects according to FIT

Answer 8

1) By attending to a location. Attention is a binding glue
2) By using stored knowledge if the object is familiar and so has characteristic features e.g. a carrot
3) By randomly combining features which may be correct sometimes but may also result in “illusory conjunctions”

Question 9

When are illusory conjunctions most likely to occur? How did Treisman (1982) conclude this?

Answer 9

When attention is overloaded. Participants were shown from left to right a “number, 3 different coloured letters and another number” for a brief time. Their job was to recall the numbers and then the letters. The shorter the presentation time, the greater the P(of Pps reporting illusory conjunctions between letters & numbers)

Question 10

The illusory conjunction evidence suggests that when attention is not available random conjunctions must be made. Why might we not trust it?

Answer 10

Because participants may not have perceived the illusory conjunctions but simply have guessed what they were from memory

Question 11

What was the deficit of patient RM (Friedman-Hill, 1995)? How was this confirmed? What brain damage had he incurred?

Answer 11

An inability to correctly combine features using attention = a dysfunctional master map, resulting in the perception of illusory conjunctions. Was shown 2 objects & then asked to recall the shape & colour of the 1st. Parietal-occipital lesion

Question 12

Name a style of presentation and external spotlight which could be used to improve patient RM’s performance. Has the finding been replicated by rTMS studies?

Answer 12

Successive rather than simultaneous presentation. A cardboard tube. Yes

Question 13

Name the 3 pieces of evidence covered which are in support of FIT

Answer 13

1) The serial vs. parallel processing effects in display size
2) Illusory conjunctions
3) Neurophysiological plausibility

Question 14

According to Van der Burg (2008) auditory cues can facilitate target detection (reduce RTs) by drawing attention to the target’s characteristics. How was this demonstrated?

Answer 14

By playing a tone, the pitch of which alternated at the same rate as the green/ red colour of the target

Question 15

Nakayama & Silverman (1986) presented Pps with a target defined by a conjunction of features which popped out, which is against the predictions of FIT. What was the conjunction? Why might this not really be a conjunction? A second e.g. was presented by McLeod (1988) - what was it & can it be trusted?

Answer 15

1) A conjunction of stereoscopic depth and colour e.g. respond to the white object in the far display. Because Pps may have fully ignored the near plane. 2) A conjunction of movement & form (shape). Pps may have moved their eyes in line with stimulus motion but the effect remains even after ensuring Pps fixate

Question 16

Kim & Cave (1995) found an e.g. of single feature search which was serial. What was it?

Answer 16

The same reduction in the % of letters recalled correctly was found when this unspeeded task was performed after making a speeded response to a target defined by a feature or conjunction. This suggests attention is allocated to the target’s location even in single feature search

Question 17

Mack & Rock (1998) found another e.g. in which a target defined by a single feature did not pop out without attention - what was it?

Answer 17

Pps were asked which of 2 lines were longer. Between the lines were green circles & 1 pink circle. The unique colour stimulus didn’t pop out during inattentional blindness for 44% of Pps= the pop out effect requires the target to be predefined (which it is not in luggage scanning) & so involves attention

Question 18

The pop out effect also fails when the target is defined by a single feature but remains…or….(Duncan & Humphreys, 1989) This is not accounted for by FIT & suggests that search task difficulty lies on a ___ I.e. search is not categorically either ___ or ___ & we do not look categorically for either features or conjunctions

Answer 18

1) Very similar to the distractors e.g. the target may be shorter than distractors but only by a marginal amount or 2) the distractors are not uniform & so cannot be grouped e.g. the target may be shorter than distractors but by differing amounts for each distractor. Continuum. Serial or parallel

Question 19

A flat search slope (RT or accuracy against display size) indicates ___ search. A steeper search slope may indicate…or…

Answer 19

Parallel. Serial search or a noisy parallel search

Question 20

Wolfe (1989) found that a triple conjunction search was ___ than a standard conjunction search. This supports the ___ ___ model: search can be guided to specific locations in the ___ map by info in the ___ map

Answer 20

Easier. Guided search model. Master map. Feature map

Question 21

Give 4 previously discussed pieces of evidence against FIT

Answer 21

1) some conjunctions are detected by parallel search
2) attention is sometimes requires for feature search
3) the serial/ parallel distinction is unclear
4) illusory contours may be a product of memory rather than perception

Question 22

Name 2 pop out effects which suggest that visual search mechanisms have evolved to aid survival

Answer 22

1) The stare-in-the-crowd effect (eyes staring at us) stand out from other eyes looking elsewhere
2) A dead (upside-down) elephant pops out from live (upright) elephant distractors but not vv

Question 23

Describe the Kaniza figure and bump pop out effects. What do the crowd, elephant and bump pop out effects suggest about what does not tend to pop out? Can the elephant and bump pop out effects be explained by FIT?

Answer 23

1) A Kaniza square pops out from non-Kaniza arranged
2) Finding the bumps amongst unbumps is easy vs. finding the unbumps amongst bumps is hard. Regular or familiar objects. No

Question 24

Real-word visual search differs in 3 ways from lab visual search. What are these 3 ways?

Answer 24

1) The target is not predefined. 2) The target does not appear on 50% of trials, instead it appears very rarely: the less often a targets appears, the more likely it is to be missed when it does appear. Software-implanted targets must be varied. 3) Targets overlap with distractors

Question 25

Desynchronised neural activity in response to…may explain why serial search is inherently poorer & slower

Answer 25

Different parts or features of the same object

Question 26

Neisser (1964) made 3 findings re: visual search for letters in columns of lines of jumbled text. What were they?

Answer 26

1) Pps are faster to search for a letter than for the absence of a letter because presence detection takes on average half the time. 2) The lower the position of the target, the longer search takes. 3) Finding a target (e.g. z) is quicker when surrounded by distractors which are very different to the target (e.g. non-angular letters)