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
implication of stroop effect
® This tells us that there is parallel processing of colour naming and word reading.
® Word reading is fast and involuntary, with the name of the word being available before the name of the colour (colour naming is slow and controlled). This creates an output interference (known as the Stroop effect)
® These processes are asymmetrical – there is no interference of ink colour on word naming (because word naming in the faster process)
® Automaticity
Learned stimulus-response associations make a process automatic. For a process to be automatic, it must be fast, carried out in parallel, effortless and not require capacity/allocation of attention. Automaticity forms the basis for skill acquisition (e.g. reading, driving, playing a musical instrument)
Controlled and automatic processing (Shiffrin & Schneider, 1977)
Search for digit targets in arrays of distractor letters in rapid sequences (or vice versa)
® Involved searching for digit targets in arrays of distractor letters in rapid sequences (or vice versa). In the consistent mapping (CM) condition, target and distractor sets were distinct. In the varied mapping condition, targets on some trials were distractors on others
Result of Controlled and automatic processing (Shiffrin & Schneider, 1977)
Performance under CM became automatic with practice (>90%)
Became independent of memory set and display size
Subjectively effortless, spontaneous pop-out of targets from text
Never became automatic under VM
Requires consistency of target set membership
Consistent with capacity-free, effortless encoding account
The Eriksen Flanker Task
-Shows a failure of focused attention – the involuntary processing of flankers even when attempting to ignore them.
Is the central character an E or an F? – measure RT
RT(compatible) < RT(neutral) < RT(incompatible)
Involuntary processing of flankers even when attempting to ignore them
Implication of flanker task
Implies some parallel processing of conjunction stimuli
Failure of focused attention
Decreases with spatial separation, disappears at 1-1.5
degrees
Provides estimate of size of focus of attention (“spotlight”)
Stimuli falling within spotlight processed automatically
Attention in Time: The Attentional Blink
Rapid serial visual presentation (RSVP) task
100 ms exposure per item; each item masked by following item
Two targets: report the white letter, detect whether there was an “X” present
Result of Attention in Time: The Attentional Blink
Plot second target (T2) performance as a function of the time (lag) since the first target (T1)
T2 performance declines and then recovers – “attentional blink”
Implication of attention blink
Only find it if T1 is processed; if T1 ignored no attention blink
Depends on T1 processing
Worst performance not immediately after T1 but some time later (Lag 1 sparing)
Effect takes time to build up, but relatively long lasting (up to 600 ms)
