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Task Switching Rogers Monsell 1995 Monsell 2003

Overarching Cause.

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Task Switching Rogers Monsell 1995 Monsell 2003

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    1. Task Switching Rogers & Monsell (1995) Monsell (2003)

    2. Overarching Cause “Cognitive processes require control processes to organize them, but these ‘executive’ mechanisms are – to put it mildly – poorly understood.” (Rogers & Monsell, 1995, p. 207) The task-switching paradigm tries to directly tap into these executive mechanisms

    3. PRP = doing two tasks on each trial Task Switching = doing one of two tasks on each trial Switching tasks causes our responses to be: Slower Less Accurate Is this true even when given sufficient time to prepare for the change in task?

    4. Task-Set Definition: the set of processes and responses that are necessary to complete the current task

    5. Task-Set Definition: the set of processes and responses that are necessary to complete the current task Task-sets can be activated by: the stimulus e.g. Stroop task GREEN BLUE = endogenous

    6. Task-Set Definition: the set of processes and responses that are necessary to complete the current task Task-sets can be activated by: the stimulus e.g. Stroop task GREEN BLUE = endogenous or by intentional / voluntary control e.g. 100m sprinter = exogenous

    7. Clinical Implications Frontal lobe damage can result in: Mild – once rewarded for responding to a particular stimulus attribute, the patient is unable to stop responding in that way Severe (utilization behavior) – unable to stop complete action patterns triggered by everyday stimuli, e.g. scissors, light-switches, etc.

    8. History - Jerslid (1929) Present P w/ a list of items P repeats same task for all items or alternates on each item Some alternations had no effect Add 3 to a #, Write antonym, Add 3, Antonym Others had large effects Add 3, Subtract 6, Add 3, Subtract 6 Not much other research until mid ’90s

    9. Modern Paradigm Train Ps on 2 simple tasks Then, do a block in which Ps sometimes alternates tasks, sometimes repeats tasks Task normally determined by: Alternating runs: n trials of each task n = 2: A A B B A A B B A A Task-cuing: cue appears before or w/ stimulus Switch & non-switch trials in same block

    10. Switch – non-switch = switch cost Predictions: long enough R-S interval & predictable task sequence ? no switch cost

    15. Method R-S interval: 150, 300, 450, 600, 1200ms R-S interval random (unblocked) in Exp’t 2, blocked in Exp’t 3 & 4. Practice: 200 trials on each task individually Experimental: ? 2,000 trials (in 2 sessions)

    16. Crosstalk

    19. Conclusions Task-set needs to be reconfigured when changing tasks, which takes time. Only ? 1/3 of the switch cost eliminated by preparation. “Participants’ inability to use a preparatory interval to get themselves into the state they would have been in had they just performed the same task appears to be a robust phenomenon.” (Rogers & Monsell, 2003, p. 223)

    20. Explanation Stimulus cue completion hypothesis: “Completion of the reconfiguration is trigerred only by, and must wait upon, the presentation of a task-associated stimulus” (Rogers & Monsell, 1995, p. 224) Endogenous processes can do some of the work, but exogenous processes needed to complete it.

    21. Experiment 6 Alternate tasks after 4 repetitions: A A A A B B B B A A A A B B B B

    23. Overall Effects Switch cost / task-repetition benefit RTs longer on switch trials than on repetition trials (˜200ms), and error rate higher Preparation effect Switch cost reduced if P has advance knowledge of task Residual cost Preparation effect levels off at ˜600ms of prep’ time without the switch cost ever entirely disappearing Mixing cost Even after many repetitions of one task, RT is still slower than in one-task situation

    24. Switch Cost Sources Task-set reconfiguration (TSR) = mental gear changing. Can include: Shifting attention b/w attributes Retrieving S-R mappings Adjusting response criteria Inhibit prior task-set

    25. Language Goschke (2000): saying an irrelevant word in preparation interval eliminated preparation effect relative to naming the next task or saying nothing Others found repeating irrelevant word throughout task hurts more on switch trials Language effects may disappear w/ practice as representation of task instruction become procedural rather than verbal

    26. Discussion Switching between tasks obviously has consistent and robust effects These costs should be considered in human-machine interface design (e.g. ATC)

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