What Processes Occur During Preparation For A Task-switch?

What Processes Occur during Preparation for a Task-switch?

Introduction When you move from one task to another, performance is worse than if you were to continue at the original task, this is known as the 'switch cost' (Rogers & Monsell, 1995). This cost has been investigated using the task-switching paradigm, where participants quickly switch between carrying out two tasks. This research has produced behavioural evidence of the 'switch cost', in the form of increased errors and longer response times (Rogers & Monsell, 1995). Additionally, it has been found that this cost can be reduced when time is given for preparation of the specific task (Meiran, 1996). It has been suggested that this preparation allows task-set reconfiguration (TSR) processes to occur before the task is performed (Rogers & Monsell, 1995; Meiran, 1996). However, there is some disagreement as to what these processes are, when they are occurring and whether they can be endogenously controlled. Therefore, this study aims to investigate the nature of these cognitive processes occurring during preparation. Behavioural Phenomena in Task Switching One influential theory suggested to explain the switch cost is that these costs represent time taken for 'task-set reconfiguration' (TSR) (Rogers & Monsell, 1995). When switching tasks the required 'task-set' (the appropriate actions, processes and responses needed to perform a task) needs to be activated, or brought into working memory (Rogers & Monsell, 1995; Mayr & Kliegl, 2000). The reduction in switch cost (RISC effect) with preparation suggests that these TSR processes can occur in anticipation of the stimulus (Rogers & Monsell, 1995). This has been investigated by varying the cue-stimulus interval (CSI), the time between the presentation of a cue informing which task to perform and the presentation of the stimulus (Meiran, 1996). However, the preparation effect does not completely eliminate the switch cost; instead a 'residual cost' remains (Rogers & Monsell, 1995; Meiran, 1996). This remaining cost has been consistently found, even when a much longer time is given for preparation (Rogers & Monsell, 1995. One explanation for this enduring cost is that it represents elements of task-set reconfiguration which can only occur in response to the stimulus (Yeung & Monsell, 2003). This may represent a distinction between 'strategic' and 'automatic' processes, with perhaps strategic processes, or those under endogenous control, occurring during preparation (Wylie & Allport, 2000). The later exogenous processes may only occur following the presentation of the stimulus (Monsell, Yeung, & Azuma, 2000). Another explanation is that task-set reconfiguration could be an 'all-or-none' process and therefore the residual cost represents a percentage of trials where this preparation fails (De Jong, 2000). What processes constitute Task-Set Reconfiguration? There is, therefore, behavioural evidence which suggests TSR processes can occur in anticipation of the stimulus. Consequently, research has considered the nature of these processes. Cognitive experiments generally involve quite simple tasks, often stimuli are the same for both tasks and the same set of responses are used (Monsell, 2003). Therefore, the differences in task-set which would need to be adjusted can be inferred fairly easily. For example, Meiran (2000) proposes that task-set can be decomposed into stimulus set and response set components. Tasks therefore differ in the features of the stimulus that are relevant and the appropriate stimulus-response mappings (Altmann, 2004), both of which would need to be reconfigured. Kiesel et al., (2010) conclude that theoretical accounts tend to agree with this judgement - that preparation includes a strengthening of task-relevant features and retrieval of stimulus-response rules. As behavioural measures cannot offer direct insight into the processes occurring during the CSI, neuropsychological studies have provided further information as to their nature. Lavric, Mizon, & Monsell, (2008) identify potential correlates of preparation for a task switch; a widespread posterior positivity and concurrent right anterior negativity prior to the stimulus onset with effective preparation. On ineffective trials a similar component was observed, but later - following the presentation of the stimulus. Karayanidis et al., (2010) suggest the cue-locked positivity and slow frontal negativity represent anticipation of the stimulus and of response selection, respectively. This would suggest that both processes can occur in the CSI. However, Meiran's (2000) model argues that although stimulus representation can be dynamically controlled by selective attention, the dynamic control of response representation cannot. Therefore, response representation must occur following the stimulus, explaining residual costs. Alternatively, Merian, Kessler, & Adi-Japha's (2008) CARIS model suggests the opposite; the reconfiguration of attentional processes can only occur following the presentation of the stimulus, whereas those relating to response selection occur during the CSI. However, Rushworth, Passingham, & Nobre (2005) provided evidence that attention can be reconfigured in the CSI by manipulating the dimension which needed to be attended to in the task. ERPs revealed early (from ~360ms post-cue) switch-repeat differences in the form of a negative modulation over the right lateral frontal scalp and a positive modulation over the left posterior scalp. As the response required was kept constant, this suggests participants were reconfiguring their attention to the appropriate dimension of the shape prior to stimulus onset. It is also debated whether reconfiguration processes are under endogenous or exogenous control, or a combination of both. It was originally thought that TSR processes were activated intentionally by the individual (Rogers & Monsell, 1995). In support of this, Koch (2008) found that encouraging participants to prepare led to increased RISC effects. It is suggested that this encouraged the participants to use the CSI to carry out enhanced monitoring processes in working memory. Further support for endogenously controlled processes comes from Dreisbach & Haider (2006) who found preparation could be dynamically adjusted by participants in response to difference situations, such as where there was a high or low percentage of repeat or switch trials. However, alternative accounts have argued explanations which do not require an endogenous act of control are sufficient to explain the preparation effect. Logan & Bundesen (2003) suggest that RISC effect could reflect the occurrence of simpler processes in the CSI such as priming of cue encoding. Alternatively, it has also been suggested that retrieval of the relevant task-set could be cued automatically by the cue (Schneider & Logan, 2005). It is also possible that TSR consists of a mixture of both endogenously and exogenously controlled processes. Koch & Allport (2006) suggest that the distinction between processes which occur during the CSI and following the stimulus may represent a disassociation between these endogenous and exogenous processes. Present Study & Hypotheses Koch (2008) manipulated instructions given to participants according to whether they encouraged preparation, finding clear evidence that performance was better with encouragement. This study will manipulate the instructions given to participants to encourage the use of different preparatory strategies, shifting of attention and retrieval of stimulus-response mappings. Behavioural data and ERPs will be compared within these conditions and with a control group. An observable cost of switching tasks is expected across all conditions, in the form of increased errors and longer reaction times (RTs), which is reduced with time given for preparation. Greater RISC effects may be found in the experimental group compared to the control group as a result of encouragement to prepare from the instructions. However, as participants are also encouraged to prepare in the control group (although not specifically) it is possible this is sufficient to increase performance and it is therefore not possible to do so further. More insight into the effect of the instruction manipulation is expected from the ERP results. Previous research suggests that preparatory processes can be observed during the CSI with ERP analysis (Rushworth et al., 2005; Astle, Jackson, & Swainson, 2008; Lavric et al., 2008). We therefore expect to observe significant switch-repeat differences in the ERPs during long CSIs, consistent with those previously found, reflecting preparatory processes. The pattern of switch-repeat differences observed in the ERPs may differ across the conditions in the experimental group, reflecting the endogenous implementation of different preparation strategies, according to the instructions given. We also expect these differences to inform as to how typical the processes which are encouraged (preparing attention and preparing responses) are of those normally occurring in the CSI. If the ERPs for the prepare responses and/or prepare attention conditions are similar to those in the control condition, this would suggest they constitute processes which are normally occurring in the CSI. Equally, if the ERPs for either instruction manipulation in the experimental condition are significantly different to those in the control, this would suggest these do not constitute processes which normally occur during the CSI.