L7: Visual Search And Feature Binding

Question 1

What is the binding problem?

Answer 1

-in the visual system info is processed modularly. But we see/
PeReceive things as whole then?

Question 2

Outline feature integration theory

Answer 2

• all perceptual features of objects are separable from the object itself and are encoded in parallel, prior to attention
• if an object has a unique perceptual feature, it will just ‘pop out’, and there will be no need for attention
• however if an object shares features with other objects it cannot be detected from a single perceptual feature and spatial attention is needed to search all the candidates serially
• evidence shows that illusionary conjunctions can occur (e.g. Quick flash of a red square and a green circle and the individual may report seeing a red circle and a green square, or combine the two). People less likely to make an illusionary conjunction when using prior knowledge to make decision (top-down influences) e.g. Carrot lake experiment

Question 3

What is a feature search?

Answer 3

When the target does not share any perceptual features with the distractors (the item “pops out”)

Question 4

What is a conjunction search?

Answer 4

The target shares one or several features with the distractors. Therefore the target cannot be detected by inspecting only colour, or only shape (etc etc). So we need to take into account a conjunction of the two features

Question 5

What effect does increasing the number of distractors have on the search time for both single feature searches and conjunction searches

Answer 5

-single feature searches: no effect

Conjunction searchers: positive correlation

Question 6

Outline evidence against FIT (feature integration theory)

Answer 6

• easier to identify something when you can group all the distractors together and exclude them all at once
• Ts and Ls thing
• negative priming tasks:

Question 7

Evaluate FIT

Answer 7

Strengths

• an important attempt to explain what is happening within the attentional spotlight
• it has influenced thinking on a variety of topics from early sensory encoding to later attentional control

Weaknesses

• conjunction searches are faster than predicted
• similarity of distractors is influential
• neglect/extinction patients have problems with both conjunctive and single feature targets

Question 8

Outline guided search theory/dual path model

Answer 8

• in reality, people usually have expectations of when to find things and so things can be found quicker than expected (prior knowledge makes searching more efficient
• suggests that a mix of serial and parallel processing strategies are used for visual search (FIT on the other hand suggests initial parallel processing and the serial )
• early pre-attentive processes produce an activation map, where each item in the display has its own level of activation (according to how “promising” it is). The object with the greatest activation receives attention first and target features receive greatest activation
• suggests there is a selective (serial) pathway with an attentional bottleneck
• there however is also a non-selective parallel pathway that allows observers to take in the gist of a scene, and to activate prior knowledge

Question 9

(Spatial attention):Outline Posner’s attentional systems (based off posners covert attention experiment: endogenous cues - arrows; and exogenous cues-square)

Answer 9

-we have two systems, an endogenous system and an exogenous system (parietal lobes it seems)

Endogenous:

• top down and goal driven
• controlled by the individuals intentions and expectations
• involved when informative, central cues are presented

Exogenous:

• bottom-up stimulus driven
• automatically shifts attention
• involved when uninformative peripheral cues are presented
• stimuli that are salient or that differ from other stimuli are most likely to be attended.

-posner said attention was like a spotlight: a small area is illuminated
, everything else is not, the spotlight can be moved around the visual field

Question 10

Outline Balints syndrome

Answer 10

• involves damage to the bilateral occipital-parietal cortex
• was unable to focus attention in more than one object at a time (simultanagnosia)
• particular problems when combining features of a stimulus. Made conjunction errors when seeing objects for 10 seconds

Question 11

Outline the role of the parietal lobe in feature binding

Answer 11

• activation of parietal lobe in conjunction tasks
• appears to play a major role in binding together all visual features of objects (colour, lines, concavities etc) and allows us to perceive them as a whole
• however it has been suggested that the parietal lobe might just be involved in difficult attention tasks (activation shown in the parietal lobe during conjunction tasks, but conjunction tasks are hard, may just be that instead of playing a role in feature binding). There is evidence against this theory however
• just about concluded that the parietal lobe does care a little bit about difficult but mostly about binding features in space. Also TMS on the parietal lobe affects feature binding across space, and can vary the level of illusory conjunctions
• seems it is a top-down parietal lobe system (you see what the parietal lobe tells you to see)

Question 12

(Spatial attention):Outline zoom-lens model for explaining attention

Answer 12

• attention is a flexible lens
• scope is expandable at will

Supported by LaBerge study: participants showed 5 letters of the scree, told to either lay attention to all of the, or just the middle letter. Every now and then a letter will be replaced by a number and they were told to press a button when something strange happened

Results: those paying attention to whole word, reaction time the same no matter where a outa in the word the number was shown

Those paying attention to just middle letter, reaction time considerably better when replacing number is in the middle