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Effects of Foreknowledge and Foreperiod on Task-Switching Cost Myeong-Ho Sohn John R. Anderson Carnegie-Mellon University ACT-R Workshop 1999 Introduction • Two Types of Control – 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 Consonant G7 A4 Letter Digit Vowel Even Z / ACT-R Workshop 1999 Odd Task Repetition Task Switch READY 2 sec READY G7 1 sec G7 RSI A4 1 sec A4 feedback 2 sec feedback time ACT-R Workshop 1999 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 Rogers & Monsell (1995, EXP 3) ACT-R Workshop 1999 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 ACT-R Workshop 1999 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 Foreknowledge manipulation Foreknowledge Condition Type o f Block STEP 1 STEP 2 Letter Letter Digit Digit Letter Digit Digit Letter Letter Letter Letter Digit Digit Letter Digit Digit Repetition Blocked Transition Switch Random Transition Mixed ACT-R Workshop 1999 Prediction RSI Condition Source of Benefit 200 Blocked priming +++ Repetition preparation + Blocked Switch priming … preparation + Random priming +++ Repetition preparation … Random Switch priming … preparation … 600 1500 ++ ++ + +++ … ++ … +++ ++ … + … … … … … ACT-R Workshop 1999 Experiment 1 STEP 2 Latency ACT-R Workshop 1999 Experiment 2 STEP 2 Latency ACT-R Workshop 1999 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 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 Model STEP 2 Latency ACT-R Workshop 1999 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