Week 7: Attention in Space and Time Flashcards
what are the Psychological Function of Spatial Attention? (2)
To assign limited-capacity processing resources to relevant stimuli in environment
Must locate stimuli among distractors and process (identify) them
Visual Search: Finding relevant stimuli among distractors:
Char
Objective
Display of no. of letters:
1) small display
2) large display
Identify a letter: is M present in the display.
Objective:
DV: RT of finding the letter
IV: Display size
Measure mean RT as a func of display size
Effects that account for easy VS difficult search tasks.
Pop-out effects:
Colour, orientations and form
Task 1:
Parallel Search for Feature Targets: Experiment and outcome
(Ed for Parallel Search)
Given an target to search
(vertical bar/red bar)
Look at display and respond yes or no to the presence of target.
Findings:
Mean RT doesn’t increase with display size (gradient = 0, amount of lines) for both presence/absence of target
Suggest:
We are able to compare contents of each display location with mental representation of target at the same time – parallel search.
Thus unaffected by amount of display.
Task 2:
Conjunction Targets Do Not Pop Out: Experiment and outcome
(Ed for Serial Search)
Target defined by combination of colour and orientation (with similar (1 aspect) as distractor; S11)
Findings:
RT increases linearly with display size -> we have to search for the through the display
Slope twice as steep for target absent as target present trials
Suggest:
1) Need to focus attention on target to detect it – focus attention on each item (color/orientation) in turn.
2) Constant scanning rate predicts linear RT/display size function
3) Stop when target is found
4) On average, search half the display on target-present trials, all of the display on target-absent trials
5) Constant scanning rate predicts 2:1 slope ratio
Task 3:
Pop-Out Effects With Letter Stimuli (properties)
1) Pop out when targets can be identified by a single features (straight lines among curves or vice versa) T among C & S
2) No pop out when targets can’t be identified by a single feature (straight lines among straight lines or curves among curves) T among L and F
* Although target stimuli compose of multiple features, one can identify them via a unique feature (straight among curves)
Feature Integration Theory
(Treisman & Gelade, 1980)
claims:
(S15)
1) Role of spatial attention is to bind features into perceptual compounds (a whole)
2) Each feature registered in its own feature map
3) Without attention features are free-floating, may lead to illusory conjunctions
Feature Integration Theory
(Treisman & Gelade, 1980)
Explanation of Parallel vs Serial Search
1) Parallel search
there is red map (1 feature). Therefore, we only need retinal image (no need to bind features) -> fast.
2) Serial Search
need additional step (spatial attention: to shine the spotlight on the stimulus) need to bring the maps together.
Feature Integration Theory:
Experiment:
Feature VS Conjunction Search
1) Conjunction targets require feature binding, so need focused attention – leads to serial search (linear increase)
2) Feature targets don’t require feature binding, don’t need focused attention – leads to parallel search (almost flat line for absent and present trials)
Feature Integration Theory:
Problems (limitations and faults)
1) Pop out sometimes depends on complex (compound or conjunction) object properties, not just simple features (Enns & Rensink, 1990)
a) rebuttals -> they create a new feature (depth) maybe tts y its can be identified.
2) High-level, not low-level properties predict pop out.
3) even in the original paper, the so called straight line may not be as linear as they would think.
Inconsistent with idea that pop out only occurs at level of simple features
Feature Integration Theory:
Problems (limitations and faults)
Efficient vs. Inefficient Search
Efficient vs. Inefficient Search:
1) Many tasks show intermediate pattern, don’t provide clear evidence of either serial or parallel search (between serial/parallel)
2) Wolfe: better described as inefficient or efficient search
3) No evidence of dichotomous population of search slopes; parallel and serial functions look like ends of continuum
Another Theory:
Guided Search Theory (Wolfe, 1989)
Description (S19)
1) Two-stage theory
2) Initial parallel stage provides a candidate list of possible targets
3) Second serial stage checks candidate list for targets
4) Search efficiency depends on similarity of target and distractors
5) Similar targets and distractors lead to large candidate list -> inefficient search
6) Dissimilar targets and distractors lead to small candidate list -> efficient search
*similar to eye movement and suggests:
Pre attentive processing -> stimulation tat can be extracted pre attentively to guide our attention.
Gaps/Failures of Visual Spatial Attentions:
Failures of Focused Attention
1) Visual search looks at costs of divided (distributed) attention: performance decline with increasing display size is evidence of capacity limitations
2) Some situations where there is a benefit not to divide attention: avoid processing distractor stimuli
3) Limitations of focused attention and involuntary processing of irrelevant stimuli
Failures of Focused attention:
The Stroop Effect (Stroop, 1935)
Name the colour of the ink in which the word is written; measure RT
fastest (compatible: red for ink n word)
Intermediate (neutral: word not related to color)
Slow (incompatible: dif color meaning for word n color)
failure of our attention, inhibiting the conflict between the given info.
The Stroop Effect (Stroop, 1935):
Parallel processing of colour naming and word reading: incompatible
1) Word reading: “fast and automatic”
2) Colour naming: “slow and controlled”
creates output interference
=> reason its hard: the fast one is the irrelavent one
Asymmetrical: no interference of ink colour on word naming
What makes a process automatic?
Fast, parallel, effortless, doesn’t require capacity
( Learned S-R associations)
Automaticity basis for skill acquisition (reading, driving, playing a musical instrument, etc.)
Is practice enough?
Controlled and Automatic Processing: Shiffrin & Schneider (1977) => practice is not enough Details S25
1) Search for digit targets in arrays of distractor letters in rapid sequences (or vice versa)
2) Vary size of target (memory) set: 1-4 items => difficulty
3)Vary size of stimulus displays: 1-4 items
(Masking stimuli, very fast)
4) Consistent mapping (CM): target and distractor sets were distinct (always digits or numbers as targets)
5) Varied mapping (VM): targets on some trials were distractors on others
Controlled and Automatic Processing:
Shiffrin & Schneider (1977)
results
did the task become automatic?
1) Performance under CM became automatic with practice (>90%)
2) Became independent of memory set and display size
3) Subjectively effortless, spontaneous pop-out of targets from text
4) Never became automatic under VM
5) Requires consistency of target set membership
6) Consistent with capacity-free, effortless encoding account
The Eriksen Flanker Task
congruent vs incongruent tasks
rationale and procedures.
Is the central character an E or an F? – measure RT
RT(compatible) < RT(neutral) < RT(incompatible)
Involuntary processing of flankers (side letters) even when attempting to ignore them
The Eriksen Flanker Task
congruent vs incongruent tasks
results, significants
Implies some parallel processing of conjunction stimuli (similar features)
Failure of focused attention (even through we know where to focus, we still process the irrelavent ones)
Decreases with spatial separation, disappears at 1-1.5 degrees
Provides estimate of size of focus of attention (“spotlight” and central vision (?) are well matched)
Stimuli falling within spotlight processed automatically
Attention in Time: The Attentional Blink
Defination and Precedure
Attentional Blink: the 2nd target cannot be detected or identified when it appears close in time to the first.
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
Attention in Time: The Attentional Blink (AB)
Findings
s30,31
Plot second target (T2) performance as a function of the time (lag) since the first target (T1)
T2 performance declines (lowest @ position 3) and then recovers (7)– “attentional blink”
Only find it if T1 is processed; if T1 ignored no AB
Depends on T1 processing
Worst performance not immediately after T1 but some time later (Lag 1 sparing)
AB Effect takes time to build up, but relatively long lasting (up to 600 ms)
Where is the Attentional Bottleneck?
1) Translating perception into action od stimuli
Must distinguish relevant from irrelevant stimuli
Good at monitoring for relevant stimuli, rejecting irrelevant stimuli preattentatively if they are not perceptually confusable
Forming representations of relevant stimuli and making decisions about them makes us insensitive to new stimuli for 500-1000 ms (double-target deficit, AB)
limitation between processes intervening betw the stimulus and response
Single-channel theory (Welford, 1959)
Can only make one decision at a time
Single-channel theory suggest that brain’s information processing system has a filter that is used to take in necessary information and block out the rest.
