1. Effects of Foreknowledge and Foreperiod on Task-Switching Cost
Myeong-Ho Sohn John R. Anderson Carnegie-Mellon University
ACT-R Workshop 1999

2. Introduction Two Types of Control Task Switching Paradigm
Executive (e.g., foreknowledge, expectation)
Automatic (e.g., priming, utilization behavior)
Task Switching Paradigm
Two task sets
Two aspects of stimulus
Two responses mapped on to the same key
Two steps
ACT-R Workshop 1999

3. G 7
A 4
Letter
Digit
Consonant
Vowel
Even
Odd Z /
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4. Task Repetition Task Switch READY 2 sec READY 1 sec G 7 G 7 RSI 1 sec
feedback
feedback
time
ACT-R Workshop 1999

5. Switching tasks takes longer than repeating task.
Switch cost
Switch cost
Switching tasks takes longer than repeating task.
Switch cost decreases as RSI increases.
Switch cost does not disappear.
What is the switch cost about?
Repetition priming?
Less than perfect preparation for switch?
ACT-R Workshop 1999

6. Rogers & Monsell (1995, EXP 3)
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7. Two mechanisms of control
Executive control
Depends on foreknowledge
Responsible for preparation
Extent of control increases over time
Apply for both repetition and switch
Automatic control
Depends on persisting activation of the just-performed task
Responsible for repetition priming
Extent of priming decreases over time
Apply only for repetition, regardless of foreknowledge
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8. Overview of experiments
Design
Transition : repeat or switch
Foreknowledge : blocked or random transition
RSI : 200 ms, 600 ms, or 1500 ms
Emphasis
Experiment 1 : emphasis on STEP 1
Experiment 2 : emphasis on STEP 2
ACT-R Workshop 1999

9. Foreknowledge manipulation
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10. Prediction
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11. Experiment 1 STEP 2 Latency
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12. Experiment 2 STEP 2 Latency
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13. Blocked Repetition : no effect of RSI
Summary of results
Blocked Repetition : no effect of RSI
Blocked Switch : faster as RSI increases
Random Repetition : slower as RSI increases
Random Switch : no effect of RSI
Emphasis did not really have any effects.
ACT-R Workshop 1999

14. Probabilistic preparation Conflict resolution Only with foreknowledge
ACT-R model
Probabilistic preparation
Conflict resolution
Only with foreknowledge
The longer the RSI, the more likely to be prepared.
Compensates decreasing priming benefit.
Persisting activation of instruction
Base level activation
With or without foreknowledge
Effective when the instruction is repeated
The longer the RSI, the less likely to be primed.
ACT-R Workshop 1999

15. Model STEP 2 Latency
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16. ACT-R can do task switching. Questions
Conclusion
Repetition effect and foreknowledge effect are independent to each other.
Residual switch cost does not seem to be under the control of executive mechanism.
ACT-R can do task switching.
Questions
What is the process that provides the repetition benefit?
Stimulus encoding? S-R mapping rules?
Preparation for a switch can be perfect, then?
ACT-R Workshop 1999