Week 7 Flashcards
Limitations in visual attention under time pressure :
RSVP
• RSVP = rapid serial visual presentation
• Only one location, but time-pressured
• Letters, digits, words, etc visually displayed, in a single
location, one after the other at a rapid rate.
• Typically about 100 ms per item
• Ps may be asked to look out for certain targets; asked at
the end of list about items (around 15 items).
• Conceptual processing even at this fast rate of
presentation
• Post-target intrusions common
Q X Y Ps report that the X was blue
Two-target RSVP - The attentional blink (AB)
Ps ignore the digital distractors and report the letters.
The Attentional Blink - 2 targets
• If Ps must detect 2 targets in the RSVP stream,
there is a decrement in reporting T2 when it
occurs a few hundred ms after T1
• Blink extends out to about T1 + 6
• Blink is not typically observed for the T1 + 1 item
(Lag-1-sparing)
• T1 & T2 processed as one event when T2 occurs
immediately after T1?
Attentional blink and the ‘lag effect’
The time taken with the probability of getting T2 correct, given T1 correct
The Attentional Blink
• AB is found if T1 and T2 defined in the same way ( 2 digits) or differently (red letter vs. digit)
• Making T1 easier to identify/report reduces the AB
• AB reflects demands of selecting & identifying T1
• But: AB occurs if Ps have to merely detect T1 without
reporting its identity
• AB not just a recall problem: Interference is observed when a recognition test of targets is used.
• AB is strongly influenced by whether or not items precede and follow T1 and T2
• or T2 is extremely brief
• Adjacent items serve as pattern masks that curtail processing of the targets
• Pattern masks compete with targets to engage perceptual processing
• They are commonly used to ensure that brief stimuli do not reach awareness
• Ps say they didn’t see the masked word, but it may be processed sufficiently
to affect responses in tasks
The AB - putting it all together
• Multiple sources of the AB? No account explains all results (Dux & Marois, 2009)
• Evidence for “resource depletion” – capacity/structural limitations on the
number of targets identified
• Effects of T1 difficulty (more difficult à bigger AB)
• Attentional control mechanisms for selecting targets and rejecting
distractors have a role
• Discriminability of targets and distractors important
• Debate continues about role of distractors in the AB
Attentional limitations under time pressure
• Effects under time pressure = stress testing the system to find
its limits (what aspects of the task are challenging under time pressure?)
• The AB evidence suggests that consolidation of targets in WM is an
operation that can’t be done for more than one target (or target chunk) at a time
• And it may be associated with competitive or inhibitory effects for other stimuli
From RSVP to task switching
• The AB (as an example) is thought to show a “hard limit” on human
cognitive capacities
• But we have seen that issues of task control are important
• how people stop responding to RSVP distractors
• how Ps switch between demands to remember targets and ignore
distractors
• Many researchers interested in task control in its own right – the
task switching paradigm
• Domain called attentional control (also EXECUTIVE control)
Task switching
• Ps incur a time (and perhaps error) cost when they switch from
one simple task to another
• Switching is an executive control operation
• Contributes to dual task performance (e.g., Attentional Blink)
• Task set: Preparation to perform one task rather than another
• Involves selecting, linking, enabling “modules” for task
components (e.g., perception, response selection).
• Links to irrelevant modules must be disabled.
• Switch costs arise in establishing the appropriate task set &
disengaging an inappropriate set
Task-switching costs are not a new thing…
• The basis for Henry Ford’s Highland Park, Michigan plant: • Model T Ford - durable and affordable • Moving assembly line • Interchangeable parts • Workers at specific locations in the line • Still the approach used today
Task switching paradigm
• Arthur T. Jersild (1927): block of trials with only a repeated
task, block of trials where two tasks are alternated, latter
takes longer.
• Typical procedure involves AABB, AAABBB, and so on.
• Task practice, fatigue, are matched over switch trials and
same-task trials
• Usually simple responses to digits or letters
• Observe a severe “switch cost” of up to several hundred ms
when the task changes
• Even though the task changes are regular and thus
predictable
The task switching phenomenon
• Same vs. different stimuli (Jersild, 1927, & later research):
• Small switch costs if both stimuli and responses different –
e.g., number task alternating with word task
• Major cost incurred when Ps change the task and thus the
response selection rule for a common stimulus configuration
• Trivial accounts of switch costs:
• Do Ps occasionally forget what task is next?
• No. Don’t see evidence of occasional slow trials
• Instead a general slowing over the RT distribution (Fagot
1994)
Basic findings in task switching
• Rogers & Monsell, 1995, AABB paradigm:
• Stimuli – digit-letter pair, e.g., G7, B2
• A Digit task – right button for odd digit, left for even
• B Letter task – right button for vowel, left for
consonant
• Task cue: Stimulus appears in one of 4 boxes. Perform
letter task for top boxes, number task for lower boxes.
Rogers and Monsell paradigm
Letter task
Vowel (R) or consonant (L)?
Digit task
Odd (R) or even (L)?
Task alternation: Letter Letter Digit Digit Letter Letter Digit Digit
Switch trial? N Y N Y N Y N
Switch trials can be predicted; sequence is regular.
Record accuracy and latency (Reaction Time) for responses for switch vs. non-switch
trials
Classic results of Rogers & Monsell
Mean RTs for 2 days, about 880 trials per day
• Large improvement on day 2, especially switch trials
• Large switch cost (even though task switches were predictable)
• Similar performance for letter and digit tasks (similar difficulty)
Practice and task difficulty effects
• Practice
• Costs are reduced but not eliminated with practice of separate tasks &
switching tasks
• Task difficulty:
• Switching TO the easier task incurs the greater cost
• e.g., from colour naming to word naming in Stroop (Allport et al, 1994).
BLUE RED GREEN YELLOW red yellow green yellow
TASK SWITCH
• What does this result suggest about the roles of relevant task
engagement vs. irrelevant task disengagement in switch costs?
Easier to switch to the more difficult task
• Suggests that DISENGAGING from the prior
task is a major factor!
• The difficult task requires effort and
concentration, so it’s difficult to disengage
from a difficult task to engage in another task
Causes of task switching effects?
• Rogers & Monsell, 1995. Emphasis on Task Set Re-configuration
(TSR) prior to the switched task
• Can maintain 2 task sets for different tasks & stimuli.
• But with different responses for the same stimuli, need to change task
set when task changes
• Supported by manipulations of preparation time:
Task-cuing paradigm (Sudevan & Taylor, 1987).
• Odd-even judgments (task 1) and greater than/less than 5 judgments (task 2)
• P is informed by a cue before the trial which task to perform.
• Cue to digit interval varied (400 to 4000 ms).
• Switch cost decreased as interval increased to 2-3 sec.
Rogers & Monsell- switching
• Large switch cost (even though task switches were predictable)
• Cuing reduces task-switch costs but does not
eliminate them
Causes of task switching effects
• But is it preparation time or delay from the last trial that
reduces the switch cost?
• These factors were confounded in initial studies
• Meiran (1996): Varied cue-to-next-stimulus interval and last-responseto-cue interval.
• A short cue-to-stimulus interval led to a large switch cost even if there
was a long delay from the last trial.
• Implicates active preparation, not just decay of effects of prior
trial
• Involving both disengaging the past task and engaging the coming task
