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1 The Task Switching Paradigm

2 Overview Executive functions Task switching paradigms Simple phenomena Complex phenomena

3 Executive Control Executive processes deal with the control of action, thought, and emotional responses. Control is required when there is a need to change the course of action, the thought or the emotion or when there is a need to act in a manner discordant with habit. Task switching Stroop Stop Signal / Go-NoGo Control failures may have devastating consequences in human-machine interactions and are implicated in many forms of psychopathology. Miyake et al. (2000) suggested a taxonomy of executive control processes including WM updating (updating and maintaining the goal state) Shifting (flexibility) Inhibition (impulsivity) Dual-Task Coordination (?) Conflict/Error Monitoring (?)

4 Task switching paradigms How are the task instructed? From memory External cues Task cues Switch cues Self selected When are the task instructed? Before the block Before the run Before the trial How many steps the tasks have? Single-step Multi-step What are the tasks Perceptual Semantic Episodic Motor (task sequences, go-nogo, pro vs anti-saccade)

5 The VERTICAL-HORIZONTAL paradigm

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7

8 SHAPE-SIZE Paradigm SIZE Square/Big Circle/Small

9 SHAPE Square/Big Circle/Small

10 SHAPE Square/Big Circle/Small

11 Simple phenomena Correct performance among normal subjects Preparation related benefits Task switching cost and task mixing cost Task rule congruency effects Backward Inhibition

12 Frontal sub-cortical circuits (Alexander et al., 1986; Cummings, 1993) PFC Posterior C (Nearly) error free performance among normal young adults BG DM- Thalamus From Yehene, Meiran & Soroker (under revision)

13 When told to respond quickly, most of the errors committed by normal young adults (and those most strongly affected by switching and preparation) are task-errors (Meiran & Daichman, in press)

14 Task switching cost and mixing cost In the cuing paradigm, the tasks (e.g., Horizontal/Vertical) are ordered randomly, e.g., VVHVHHHV. In this sequence, some trials involve a task repetition (VVHVHHHV) and others involve a task switch (VVHVHHHV) Switching cost = performance decrement in SWITCH relative to REPEAT Mixing Cost = performance decrement in REPEAT relative to blocks without task switching (SINGLE- TASK)

15 Evidence for intention to switch Task Alternation Cost Yehene, Meiran, & Soroker, 2005

16 Rule Congruency Effect (Sudevan & Taylor, 1987) Congruent RT < Incongruent RT L Square/Big Circle/Small R SHAPE SIZE

17 Backward inhibition (Mayr & Keele, 2000) CBA ABA

18 Complex phenomena Switch asymmetry Reduction in switching cost and mixing cost by preparation Reduction in switching cost by dissipation Reversal of the response repetition effect by switching Within-run slowing Stimulus-set binding The dependence of switch cost on explicit task representation Task grouping effects Cue switch effects Instruction type Individual differences

19 All neutral: Read: GREEN Name color: XXXXX Switch asymmetry Color neutral: Read: GREEN Name color: XXXXX All Stroop Read: GREEN Name color: GREEN From Wylie & Allport, 2000

20 Reduction of switching cost and mixing cost by preparation Switching cost Mixing cost Cue-Target Interval

21 Reduction of switching cost by dissipation Group 1: 50% switch trials, RCI blocked Group 2: 50% switch trials, RCI random Group 3: 33% switch trials, RCI blocked Cost (ms) Group1 Group2 Group RCI (ms) Switching cost is reduced by increasing RCI. The effect seems relatively passive non-strategic Meiran, Chorev, & Sapir, 2000

22 RT (ms) No-Switch Group1 Group2 Group RCI (ms) Evidence for set dissipation with increasing RCI Non-switch RT increases Switch RT and switching cost decrease

23 Reversal of the response repetition effect in switch trials From Meiran, 2005

24 Altmann & Gray, 2002 Within-run slowing Monsell, Sumner & Waters, 2002

25 Stimulus-set binding (Waszak et al., 2003)

26 The task switching cost is found only when subjects know that they switch between categorical tasks (words describing living or nonliving things or beginning with a vowel or consonant, depending on the word colour). It is not found when subjects believe they are tested for their memory regarding which stimulus goes with which response. (Dreisbach et al., 2006)

27 Lien & Ruthruff, 2004 Switching cost depends on how tasks are subjectively perceived Exp1: baseline Exp2: temporal grouping Exp3:Temporal+presenting the ensemble quadrants only Exp4:When the ensemble switched, there was a switch in the presented quadrants Tasks: Large-Small (than 5) and Odd-Even

28 Mayr and Kliegl (2000) Two cue types: Spatial cue Switch costs depend on the type of task information provided by the task cue Living Colour Lion S-R cue: Living Non-Living Lion

29 Episodic SC > Semantic SC only when preparation time is short and there is a need to retrieve the task rules. Conclusion: Task control involves retrieving the task rules from episodic memory

30 Logan & Bundesen (2003) separating cue switch effects from task switch effects

31 Kray & Lindenberger, 2000 Switching cost and mixing cost represent different abilities. Mixing cost but not switching cost is related to aging.

32 Friedman & Miyake (2004): switch cost reflects inhibitory deficits

33 The Task Switching Paradigm Overview Executive functions Task switching paradigms Simple phenomena Complex phenomena Executive Control Executive processes deal with the control of action, thought, and emotional responses. Control is required when there is a need to change the course of action, the thought or the emotion or when there is a need to act in a manner discordant with habit. Task switching Stroop Stop Signal / Go-NoGo Control failures may have devastating consequences in human-machine interactions and are implicated in many forms of psychopathology. Miyake et al. (2000) suggested a taxonomy of executive control processes including WM updating (updating and maintaining the goal state) Shifting (flexibility) Inhibition (impulsivity) Dual-Task Coordination (?) Conflict/Error Monitoring (?) 1

34 Task switching paradigms How are the task instructed? From memory External cues Task cues Switch cues Self selected When are the task instructed? Before the block Before the run Before the trial How many steps the tasks have? Single-step Multi-step What are the tasks Perceptual Semantic Episodic Motor (task sequences, go-nogo, pro vs anti-saccade) The VERTICAL-HORIZONTAL paradigm 2

35 SHAPE-SIZE Paradigm SIZE Square/Big Circle/Small SHAPE Square/Big Circle/Small 3

36 SHAPE Square/Big Circle/Small Simple phenomena Correct performance among normal subjects Preparation related benefits Task switching cost and task mixing cost Task rule congruency effects Backward Inhibition Frontal sub-cortical circuits (Alexander et al., 1986; Cummings, 1993) PFC Posterior C (Nearly) error free performance among normal young adults BG DM- Thalamus From Yehene, Meiran & Soroker (under revision) 4

37 When told to respond quickly, most of the errors committed by normal young adults (and those most strongly affected by switching and preparation) are task-errors (Meiran & Daichman, in press) Task switching cost and mixing cost In the cuing paradigm, the tasks (e.g., Horizontal/Vertical) are ordered randomly, e.g., VVHVHHHV. In this sequence, some trials involve a task repetition (VVHVHHHV) and others involve a task switch (VVHVHHHV) Switching cost = performance decrement in SWITCH relative to REPEAT Mixing Cost = performance decrement in REPEAT relative to blocks without task switching (SINGLE- TASK) Evidence for intention to switch Task Alternation Cost Yehene, Meiran, & Soroker,

38 Rule Congruency Effect (Sudevan & Taylor, 1987) Congruent RT < Incongruent RT L Square/Big Circle/Small R SHAPE SIZE Backward inhibition (Mayr & Keele, 2000) CBA ABA Complex phenomena Switch asymmetry Reduction in switching cost and mixing cost by preparation Reduction in switching cost by dissipation Reversal of the response repetition effect by switching Within-run slowing Stimulus-set binding The dependence of switch cost on explicit task representation Task grouping effects Cue switch effects Instruction type Individual differences 6

39 All neutral: Read: GREEN Name color: XXXXX Switch asymmetry Color neutral: Read: GREEN Name color: XXXXX All Stroop Read: GREEN Name color: GREEN From Wylie & Allport, 2000 Reduction of switching cost and mixing cost by preparation Switching cost Mixing cost Cue-Target Interval Reduction of switching cost by dissipation Group 1: 50% switch trials, RCI blocked Group 2: 50% switch trials, RCI random Group 3: 33% switch trials, RCI blocked Cost (ms) RCI (ms) Group1 Group2 Group3 Switching cost is reduced by increasing RCI. The effect seems relatively passive non-strategic Meiran, Chorev, & Sapir,

40 RT (ms) Group1 No-Switch Group2 950 Group RCI (ms) Evidence for set dissipation with increasing RCI Non-switch RT increases Switch RT and switching cost decrease Reversal of the response repetition effect in switch trials From Meiran, 2005 Altmann & Gray, 2002 Within-run slowing Monsell, Sumner & Waters,

41 Stimulus-set binding (Waszaket al., 2003) The task switching cost is found only when subjects know that they switch between categorical tasks (words describing living or nonliving things or beginning with a vowel or consonant, depending on the word colour). It is not found when subjects believe they are tested for their memory regarding which stimulus goes with which response. (Dreisbach et al., 2006) Lien & Ruthruff, 2004 Switching cost depends on how tasks are subjectively perceived Exp1: baseline Exp2: temporal grouping Exp3:Temporal+presenting the ensemble quadrants only Exp4:When the ensemble switched, there was a switch in the presented quadrants Tasks: Large-Small (than 5) and Odd-Even 9

42 Mayr and Kliegl (2000) Two cue types: Spatial cue Switch costs depend on the type of task information provided by the task cue Living Colour Lion S-R cue: Living Lion Non-Living Episodic SC > Semantic SC only when preparation time is short and there is a need to retrieve the task rules. Conclusion: Task control involves retrieving the task rules from episodic memory Logan & Bundesen (2003) separating cue switch effects from task switch effects 10

43 Kray & Lindenberger, 2000 Switching cost and mixing cost represent different abilities. Mixing cost but not switching cost is related to aging. Friedman & Miyake (2004): switch cost reflects inhibitory deficits 11