week 7 attention in space and time Flashcards
The psychological function of spatial attention:
- To assign limited capacity processing resources to relevant stimuli in the environment.
-To do this, we must locate stimuli among distractors and process (identify) them
-We can measure visual search in terms of mean RT as a function of display size
Pop out effect
-some search target can be easily found from the background; other need attention to find
some feature that lead to pop out effect
-unique color
-unique orientation
parallel search for feature
® Mean RT doesn’t increase with display size. This suggests that we are doing this search in parallel
® We compare the contents of each display location with our mental representation of the target at the same time.
Conjunction targets
® Conjunction targets are those defined by a conjunction of features – a combination of colour and orientation
® For these targets, RT increases linearly with display size.
® The slope is twice as steep for target absent as target present trials
® This suggests evidence for serial search – we seem to need to focus our attention on the target to detect it – we need to focus our attention on each item in turn (serial search).
® Constant scanning rate predicts linear RT/display size function.
Evidence For Serial Search
® we seem to need to focus our attention on the target to detect it – we need to focus our attention on each item in turn (serial search).
® Constant scanning rate predicts linear RT/display size function.
Self-Terminating Serial Search
Stop when target is found
On average, search half the display on target present trials, all of the display on target-absent trials
Constant scanning rate predicts 2:1 slope ratio
Pop-out effects with letter stimuli
® Pop-out targets can be identified by a single feature (e.g. straight lines amongst curves, or vice versa).
® There is no pop-out when targets can’t be identified by a single feature (e.g. straight lines amongst strait lines, or curves among curves).
Feature integration theory: Triesman & Gelade, 1980:
Role of attention is to bind features into perceptual compounds
Each feature (lines, colours etc.) registered in its own feature map
Without attention features are free-floating, may lead to illusory conjunctions
Feature intergration model on conjuction and parallel search
® Conjunction targets require feature binding, so need focused attention – which leads to serial search.
® Feature targets don’t require feature binding, and therefore don’t need focused attention – which leads to parallel search
Problems With FIT
Pop out sometimes depends on complex object properties, not just simple features (Enns & Rensink, 1990)
- High-level, not low-level properties predict pop out.
Inconsistent with idea that pop out only occurs at level of simple features
Efficient vs inefficient search
® Many tasks show an intermediate pattern – don’t provide clear evidence of either serial or parallel search. Wolfe suggested that this is better described as inefficient or efficient search.
® There is no evidence of dichotomous population of search slopes – parallel and serial functions look like the ends of a continuum ranging from efficient (parallel search) to inefficient (serial search). It is unclear how feature integration theory would account for this
Guided search theory (Wolfe, 1989):
® Suggests that search is carried out not just in parallel or just serially – but in a twostage process.
® The initial parallel stage provides a candidate list of potential targets. The second serial stage checks the candidate list for targets.
® Search efficiency depends on the similarity of the target and distractors. Similar targets and distractors lead to a large candidate list & inefficient search. Dissimilar targets and distractors lead to a small candidate list & efficient search.
® There is an initial parallel processing of sensory features, which guides the allocation of a limited capacity channel.
Failures of Focused Attention
Visual search looks at costs of divided (distributed) attention: performance decline with increasing display size is evidence of capacity limitations
Some situations where there is a benefit not to divide attention: avoid processing distractor stimuli
Limitations of focused attention and involuntary processing of irrelevant stimuli
The Stroop Effect (Stroop, 1935)
® Participants were required to indicate the colour of a word presented as fast as possible.
® 3 different types of stimuli were shown (compatible (e.g. ‘red’ written in red ink), neutral (‘rain’ written in blue ink) and incompatible stimuli (e.g. ‘blue’ written in yellow ink).
® RT was fastest with compatible stimuli, intermediate with neutral stimuli and slowest with incompatible stimuli
