How do we switch between tasks? In everyday life, numerous cognitive tasks occur simultaneously which require us to implement in parallel, or in prompt alternation (Hallowell, 2007).

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                      How do we switch between tasks?

In everyday life, numerous cognitive tasks occur simultaneously which require us to implement in parallel, or in prompt alternation (Hallowell, 2007). The ability to rapidly switch between two or more cognitive tasks is known as task switching (Allport, Styles & Hsieh, 1994). For the last century, various of task switching paradigms have been established in the laboratory setting and uncover relevant function of executive control processes: executing new or partially learned tasks (Shiffrin & Schneider, 1977), prohibiting unwanted overlearned responses to Stroop stimuli (Monsell, 1996) and in shifting from competing one task to another ( Allport, Styles, & Hseih, 1994; Rogers &Monsell, 1995); These paradigms usually require subjects to accomplish a set of simple tasks in a repeating or alternating sequence(e.g., Jersild, 1927). Many task-switching paradigm studies (e.g. Monsell, 2003; Allport, Styles & Hsieh, 1994) found there are some consistently basic phenomena of task switching revealed as longer reaction time (RT) and more error-prone performances when subjects respond to switching (AB/BA) than repetition trials(AA/BB).These deficits in latencies of RT and accuracy are known as the ‘switch cost’ (Sohn , Ursu , Anderson, Stenger & Carter, 2000),which can be reduced by preparing upcoming tasks (‘preparation effect’) but cannot be abolished (‘residual cost’) (Monsell, 2003); even when performing repeat trials after a switch (e.g.,ABAA), the reaction time remains longer than when just performing one task throughout the block (e.g.,AAAA) (‘mixing cost’) (Monsell, 2003;Rubin & Meiran, 2005). These phenomena generate a question that where are the sources of these costs. An acknowledge conception of switching costs is that subjects must operate control processes to allow them to shift between performing tasks, but that the same switching control processes are not required on repeat (non-switch) trails (Wylie & Allport, 2000). So the RT(or error) switch cost can be ascribed to the cost of performing these switching control processes and RT switch cost measure the time needed to operate this mental “gear changing” (Monsell, 2003, p.135).

Many researchers have tried to elaborate on the sources of switch costs to expose the mechanisms underlying task switching implement (Monsell, 2003). Primarily, there are three theoretical explanations of origins of switch cost are appeared as: ‘task-set reconfiguration’ (TSR) processes, Transient task-set inertia (TSI) processes and task-set priming (TSP) or association retrieval (AR) processes. Are they all fundamental processes to make switch happen? If so, how do they implement in the brain? The viewpoint of this paper is that there is not ‘pure process’ but integrated processes(TSR,TSI & TSP)are contribute to switch cost and involved in the different stage of task switching performance to make shift happen. To support this thesis, firstly, the evidences of the existence of the comprehensive model in task switching will be displayed and evaluated. Then their functioning interval in task switching will be presented. Finally, the unsolved problems will be illustrated.

There is not a ‘pure process’ can fully explain the reasons of switch costs

     The three theories reveal different aspects of the task switching mechanism by partially explain the origins of switch cost. The TSR model emphasizes on the processes for reconfiguring new task-set which contributes to RT switch cost (Monsell, 2003); while the TSI model emphasizes on the passive dissipation of the prior task-set activation (carryover effect) which delays the RT (Allport & Wylie, 2000); and the TSP model underlines the delay RT is caused by the long-term priming effect which contributes by bivalent stimulus that triggering associative retrieval of task-sets (Allport & Wylie, 2000).

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A better theoretical explanation of task switching may need to contain all three sources of switch costs (an integrated model). With regards to the TSR model (Monsell, 2003),it suggested that RT switch costs reflect the time needed by performing task-set reconfiguration .It claims a task per se demands its own ‘task-set’ (Rogers & Monsell, 1995) or ‘recipe’ ( Allport, Styles, & Hseih, 1994), comprising the regulations of the task and stimulus-response (S-R) mapping (e.g. searching for targets in one position, suppressing interference in another position; if color red appears press right lever, if green press another)  (Brand,2007). To change tasks, a ...

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