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Limits on Ability to Perform Different Tasks Simultaneously Two basic issues:

Limits on Ability to Perform Different Tasks Simultaneously Two basic issues:. 1. Task- Specific Resources. 2. Task- Independent Resources. Interferes. Interferes. Verbal Judgments. Spatial Judgments. OK!. Verbal Responding. Spatial Responding. Task-General Resources.

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Limits on Ability to Perform Different Tasks Simultaneously Two basic issues:

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  1. Limits on Ability to Perform Different Tasks Simultaneously Two basic issues: 1. Task-Specific Resources 2. Task-Independent Resources

  2. Interferes Interferes Verbal Judgments Spatial Judgments OK! Verbal Responding Spatial Responding

  3. Task-General Resources Reaction Time Tasks • Simple Reaction Time (~200 msec) • Choice Reaction Time (300 msec ++) Present Stimulus Subject Responds Reaction Time

  4. stimulus stimulus stimulus 1 2 3 Task 1 button1 button2 button3 stimulus stimulus stimulus A B C Task 2 button1 button2 button3

  5. Perceptual Processing Response Production Processing Stages in Choice RT Tasks Present Stimulus Subject Responds Reaction Time Decision/ Response Selection Question: Can people do two tasks this simple at one time?

  6. Response 2 Present Stimulus 2 Reaction Time 2 Delay Psychological Refractory Period experiment (Telford, 1931) Present Stimulus 1 Response 1 Reaction Time 1

  7. There is dual-task interference! Reaction Time Reaction Time 2 Reaction Time 1 (Same results for almost all task pairs, whether similar or not.) Delay from S1 to S2 PRP effect “Psychological Refractory Period”

  8. Stimulus 1 Response 1 Reaction Time 1 Response 2 Stimulus 2 Reaction Time 2 Total Time for both task Delay Total Time < (Task1 + Task2)

  9. Response Prod. Response Prod. Perceptual Processing Response Selection Perceptual Processing Response Selection Delay Response Selection Bottleneck Model • All task elements can occur in parallel except for response selection …”slack”... Response selection for Task 2 has to wait until response selection for task 1 is completed (e.g. Pashler, 1991)

  10. stimulus stimulus stimulus A B C Task 2 easy mapping button1 button2 button3 stimulus stimulus stimulus A B C Task 2 hard mapping button1 button2 button3

  11. EasyResponse Selection Perc. Resp. Sel. Resp. Perc. Resp. Sel. Resp. Delay Perc. Resp. Sel. Resp. Perc. Resp. Sel. Resp. Delay HardResponse Selection

  12. Reaction Time 1 Delay from S1 to S2 Reaction Time 2 Delay from S1 to S2

  13. Reaction Time 1 Hard task 2 response selection = Easy task 2 response selection Delay Reaction Time 2 Hard response task 2 selection Easy task 2 response selection Delay

  14. EasyTask-2 Perception Perc. Resp. Sel. Resp. Perc. Resp. Sel. Resp. Delay Perc. Resp. Sel. Resp. Resp. Sel. Resp. Perc. Delay Hard Task-2 Perception The increased perceptual difficulty gets absorbed in the slack time, with no extra-cost for the secondary task

  15. Reaction Time 1 Delay from S1 to S2 Reaction Time 2 Delay from S1 to S2

  16. Reaction Time 1 Hard task 2 percept. = Easy task 2 percept. Delay Reaction Time 2 Hard task 2 percept. Easy task 2 percept. “Absorption into slack” Delay

  17. With no response selection bottleneck… EasyResponse Selection Perc. Resp. Sel. Resp. Perc. Resp. Sel. Resp. Delay HardResponse Selection Perc. Resp. Sel. Resp. Perc. Resp. Sel. Resp. Delay

  18. Reaction Time 1 Hard task 2 response selection = Easy task 2 response selection Delay Reaction Time 2 Hard response task 2 selection Easy task 2 response selection Delay If there is absolutely no bottleneck…then there will be a constant difference between easy and hard task 2 RT across all delays…in addition, there should be no rise in RT at even the shortest delays...

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