Absence of perceptual processing during reconfiguration of task set

The authors manipulated stimulus contrast and response-stimulus interval in the alternating runs paradigm to investigate whether early processing could be carried out during a task switch. Subjects alternated between judging the magnitude and the parity of a digit. The results suggested that early processing was not carried out during the task switch (Experiment 1), even in the absence of potentially confounding auditory or visual warning signals (Experiment 2). This processing was, however, carried out in parallel with a demanding operation in a 2nd task (Experiment 3), using the display parameters of Experiments 1 and 2 in the psychological refractory period paradigm. It is concluded that, functionally, task switching may impose a hard bottleneck even for very early stimulus processing. ((c) 2003 APA, all rights reserved)     

Eye movements, not hypercompatible mappings, are critical for eliminating the cost of task set reconfiguration

Residual switch costs are notoriously difficult to eliminate. Yet Hunt and Klein (2002) eliminated them in a task that required observers to alternate between 8 trials of prosaccades and 8 trials of antisaccades, as long as there was at least 1 sec between the task cue and the onset of the saccade target. It was proposed that the elimination of residual switch costs occurred because prosaccade responses are computed very rapidly. These so-calledhypercompatible responses bypass memory retrieval stages of the response process, thereby eliminating the source of residual switch costs. Here we tested this hypothesis by requiring observers to alternate between responding with the finger that was vibrated (another task that meets the criteria for hypercompatibility) and responding with the finger of the opposite hand. Residual switch costs were not eliminated, suggesting that their elimination in Hunt and Klein (2002) was due to special properties of the prosaccade—antisaccade task.     

The reconfiguration of task set has no effect on the efficiency of feature search

In this study, we investigated whether or not the reconfiguration of a set task could modulate the efficiency of feature search. In Experiment 1, target set size was manipulated. The results revealed that enumerating targets defined by color yields a much steeper slope when executed simultaneously with a discrimination task than when done singly. However, when distractor set size was manipulated, there was no significant difference in the efficiency of individualizing targets from distractors between the two task conditions, no matter whetherthe search was guided by bottom-up information (Experiment 2) or top-down information (Experiment 3). Drawing upon these results, the authors propose that (1) an additional task can impair the efficiency of enumeration, resulting in a steep slope of counting even when target set size is quite small, and (2) in feature search, the visual system first reconfigures the task set to match the input feature information and then detects the targets with an optimal efficiency, which does not support the theory proposed by Di Lollo, Kawahara, Zuvic, and Visser (2001; Di Lollo, Smilek, Kawahara, & Ghorashi, 2005).     

Exploring task-set reconfiguration with random task sequences

Switching between two different tasks normally results in an impairment in people's performance known as a switch cost, typically measured as an increase in reaction time (RT) and errors compared to a situation in which no task switch is required. Researchers in task switching have suggested that this switch cost is the behavioural manifestation of the task set reconfiguration processes that are necessary to perform the upcoming task. However, an examination of the literature in task switching reveals apparently contradictory results about the nature of task set reconfiguration processes. In Experiment 1, we addressed this issue by comparing participants' performance in two different experimental conditions: predictable task switching and random task switching. In the predictable switch condition the switch cost completely vanished after the first repetition of the new task. However, in the random switch condition, while the difference between switch and repetition trials was not significant, we observed a significant reduction in RT between the first and second repetition of the new task. In Experiment 2, we further investigated the pattern of task set reconfiguration in the random switch situation. The results showed a progressive reduction of participants' response latencies across repetitions of the same task. The present study demonstrates that, whereas the results in predictable switching conditions are compatible with an exogenous-reconfiguration hypothesis, random task switching produces a more gradual, decay-like switch cost reduction with task repetition.     

Task-set reconfiguration with binary and three-valued task dimensions

 Recently, we [Kleinsorge & Heuer (1999) Psychological Research, 62, 300–312] introduced the notion of generalizing switching operations to account for a characteristic pattern of shift costs that can be observed when participants have to shift between four tasks that result from an orthogonal combination of the two binary task dimensions kind of judgment (numerical vs spatial) and judgment-to-response mapping (compatible vs incompatible). Specifically, while a change of the kind of judgment always results in costs, a change of mapping results in costs only when the kind of judgment is repeated, but results in benefits when the kind of judgment changes as well. In Experiment 1, we replicated and extended this finding with a combination of two spatial kinds of judgment that were more similar to each other and were more unlikely to result in build-in dependencies of the two task dimensions. In Experiment 2, we extended this design to a combination of nine tasks that resulted from a factorial combination of two three-valued task dimensions. In this experiment, shift costs grew monotonically with the number of task dimensions on which a change took place. This outcome is consistent with the assumption that a generalizing switching operation is a forward-acting process that requires a specific target value to switch to. Received: 17 April 2000 / Accepted: 25 August 2000     

Task-set reconfiguration with predictable and unpredictable task switches

Participants switched frequently between high/low and odd/even classification of a digit. The interval between a task cue and the next digit varied between blocks. In Experiment 1, the task switched predictably every two, four, or eight trials. In Experiment 2, switching predictably every four trials was compared with random switching. With predictable switching, the cost was limited to the first trial of a run. Random switching produced a more gradual approach to asymptotic performance. After one performance, control processes attenuate the resulting change in task-set bias if a further switch is likely, but this strategic modulation is soon overwhelmed by task-set priming through further performances. Preparation reduced switch costs but not interference from the irrelevant attribute: Control of interference appears to be reactive, not proactive. Switch costs did not increase with run length, suggesting that retrieval of the task set last associated with the stimulus did not contribute to switch costs.     

Electrophysiological evidence for preparatory reconfiguration before voluntary task switches but not cued task switches

An unresolved issue in the task-switching literature is whether preparatory reconfiguration occurs before a change of task. In this study, we used event-related potentials (ERPs) to determine whether preparatory reconfiguration occurs during two different task-switching procedures: voluntary and cued task switching. We focused on two ERP components that index different cognitive operations. The contingent negative variation (CNV) is a sensitive measure of a participant’s preparedness to use a specific stimulus–response mapping. In contrast, the P3 indexes memory updating. We found a pronounced modulation of the CNV before voluntary task switches, but not before cued task switches. Instead, cued task switches were preceded by a larger P3, as compared with task repetitions. Our findings suggest that task set reconfiguration is carried out prior to voluntary task switches, whereas memory processes dominate cued task switches.     

Exogenous influences on task set activation in task switching

To explore the effect of exogenous processes on cognitive control, we used a cueing task-switching paradigm with two spatial judgement tasks and added an irrelevant colour attribute to the task-relevant spatial attribute of the target. The colour was not related to any specific Stimulus-Response relation in the tasks. A correlation was created between stimulus colour and task identity. This correlation was strong but imperfect in Experiment 1 and perfect in Experiment 2. As a result of the colour-task correlation, stimuli contained redundant information about task identity. By changing the correlation pattern every few blocks we caused this information to be sometimes invalid. In both experiments, performance was worse when the information carried by the target was invalid than when it was valid. However, this effect was exclusive to conditions with short task preparation time. By comparing performance with a control group, which had no colour-task correlation (in Experiment 2) we established that the colour manipulation did not cause a qualitative change in preparation strategy, and that the exogenous effect was stronger in switch trials than in repetition trials. We conclude that exogenous processes that are related to task set affect performance primarily if they are presented before endogenous processes of task set preparation have been launched.     

Exogenous influences on task set activation in task switching

To explore the effect of exogenous processes on cognitive control, we used a cueing task-switching paradigm with two spatial judgement tasks and added an irrelevant colour attribute to the task-relevant spatial attribute of the target. The colour was not related to any specific Stimulus–Response relation in the tasks. A correlation was created between stimulus colour and task identity. This correlation was strong but imperfect in Experiment 1 and perfect in Experiment 2. As a result of the colour–task correlation, stimuli contained redundant information about task identity. By changing the correlation pattern every few blocks we caused this information to be sometimes invalid. In both experiments, performance was worse when the information carried by the target was invalid than when it was valid. However, this effect was exclusive to conditions with short task preparation time. By comparing performance with a control group, which had no colour–task correlation (in Experiment 2) we established that the colour manipulation did not cause a qualitative change in preparation strategy, and that the exogenous effect was stronger in switch trials than in repetition trials. We conclude that exogenous processes that are related to task set affect performance primarily if they are presented before endogenous processes of task set preparation have been launched.     

Dissociating restart cost and mixing cost in task switching

Three experiments investigated the cognitive mechanisms underlying the restart cost and mixing cost in task switching. To this aim, the predictability of task order was varied (unpredictable in Experiment 1 and predictable in Experiments 2 and 3) across experiments, which employed a multiple-trial paradigm. Verbal cues for color and shape matching tasks were presented before a run of four trials. Focusing on task-repetition runs only, we measured restart cost as the difference in performance between trials 1 and 2 and mixing cost as the difference in performance on the non-cued trials under mixed-tasks conditions (Experiments 1 and 2) and single-task conditions (Experiment 3). The restart cost was observed under mixed-tasks conditions with both unpredictable and predictable task orders but not under the single-task condition. In contrast, the mixing cost was observed under the mixed-tasks condition with unpredictable task order only (Experiment 1). This finding implies that the optimal task execution on repetition trials depends on how predictable the identity of the approaching task is. Therefore, we suggest that mixing cost arises from limited preparation on repetition trials when task order is unpredictable, while restart cost arises from processes involved in cue-based task activation that is needed to resolve task interference. Together, these data suggest that restart cost and mixing cost are based on dissociable mechanisms.

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The role of external cues for endogenous advance reconfiguration in task switching

Most studies of task-set switching rely on cuing paradigms, in which external cues indicate the upcoming task. The present study used an entirely predictable task sequence in a variant of the alternating-runs paradigm of Rogers and Monsell (1995). Preparation effects with purely internal memory cues were compared with those in another experimental group with additional external cues presented prior to the stimulus. External cues led to strongly reduced shift costs with prolonged preparation time. However, this effect was much smaller with internal cues only. To account for this differential effect of preparation time as a function of cue type, it is suggested that internal cues select the next task set, which is sufficient to perform the task. External cues additionally facilitate preparatory retrieval of task-specific stimulus-response rules. This account may also explain why incidental task-sequence learning based on internal cues did not reduce shift costs.     

Cost of mental set reconfiguration between digits and their photisms in synaesthesia

In this study we present an experiment investigating the reconfiguration process elicited by the task switching paradigm in synaesthesia. We study the time course of the operations involved in the activation of photisms. In the experimental Group, four digit-color synaesthetes alternated between an odd-even task and a color task (to indicate the photism elicited by each digit). In both tasks, the target stimuli were numbers between 1 and 9 written in white. One of the control groups ran the same tasks but this time with colored numbers (Naive Control Group). The results of these studies showed the expected pattern for the control group in the case of regular shift: a significant task switch cost with an abrupt offset and a cost reduction in long RSI. However for the experimental group, we found switch cost asymmetry in the short RSI and non-significant cost in the long RSI. A second control group performed exactly the same tasks as the experimental group (with white numbers as targets and a second imaginary color task) -Trained Control Group-. We found no cost for this second control group. This means that the cost of mental set reconfiguration between numbers (inducers) and their photisms (concurrent sensations) occurs, that there is a specific cost asymmetry (from photisms to inducers) and that this cost cannot be explained by associative learning. The results are discussed in terms of exogenous and endogenous components of mental set reconfiguration.     

Nonintentional task set activation: Evidence from implicit task sequence learning

Studies have shown that task sets could be configured endogenously (i.e., on the basis of memory) according to an explicit sequence or exogenously according to a task cue. In two experiments, we examined whether an implicitly learned sequence could facilitate task set configuration without participants’ intention. These experiments led to opposite conclusions regarding this question, but their methodology made it impossible to distinguish between the interpretations. We altered the task-switching paradigm by embedding a hidden task sequence, while randomizing all other aspects, including perceptual (i.e., task cues) and motor elements. We found that a sequence of tasks, proper, was learned implicitly and that the memory of that sequence endogenously facilitated task decision processes without the participants’ explicit knowledge.     

A more complete task-set reconfiguration in random than in predictable task switch

Three experiments are presented that compare the cost found when switching from one task to another in two different conditions. In one of them, the tasks switch in predictable sequences. In the other condition, the tasks alternate at random. A smaller time cost is found in the random-switch condition when enough preparation time is allowed. Such an effect is due to the random-switch cost continuing to decrease with preparation time after the predictable-switch cost has reached an asymptote. Although the relationship between number of repetitions of one task and time cost is different in the random- and the predictable-switch conditions, only the latter shows the presence of an exogenous component of cost. The implications of this finding are discussed in relationship with the usual distinction between an endogenous component of switch cost that is affected by preparation time and another exogenous, residual component (e.g., Rogers & Monsell, 1995). It is proposed that a different kind of task-set preparation is at work when tasks alternate at random.     

The cost of a voluntary task switch

Task-switching paradigms are widely used to study executive control. However, standard paradigms may not require active control to switch tasks. We examined voluntary task switching by having subjects choose which task to perform on a series of bivalent stimuli. Subjects performed parity or magnitude judgments on single digits. Instructions were to perform the two tasks equally often and in a random order. The response-to-stimulus interval (RSI) was either 100 or 1,000 ms, manipulated between blocks. Task alternations were slower than task repetitions, and this switch cost was greater at the short RSI than at the long RSI (310 and 94 ms, respectively). Additionally, subjects produced more task repetitions than expected if the tasks were performed in a random sequence. These results show costs associated with a voluntary task switch, when subjects must actively control the choice of the task to be performed.     

Selective attention and response set in the Stroop task

Response set membership contributes much to the interference in the color-word Stroop task. This may be due to selective allocation of attention to eligible responses or, alternatively, to greater inhibition of distractors that are not responses. In the present article, we report two experiments that were designed to adjudicate between these accounts. In Experiment 1, membership was manipulated on a trial-by-trial basis by cuing the possible responses for each trial. Response time (RT) was longer for distractors that corresponded to a cued, eligible response than to an ineligible one. This cuing effect was independent of the number of different responses. In Experiment 2, the distractor was cued on half the trials. Cuing the distractor decreased RTs on both incongruent and congruent trials. Vincentile analyses in both experiments revealed that the effects were constant throughout the entire RT distributions. These results suggest that response set effects arise because of selective allocation of attention to eligible responses.     

Inhibition of task set: Converging evidence from task choice in the voluntary task-switching paradigm

This study looked for evidence of task-set inhibition in a voluntary task-switching paradigm. Participants performed one of three tasks on a digit: parity (even or odd), size (less than or greater than 5), or distance (near or far from 5). On each trial, they were allowed to choose which task to perform, with encouragement to perform each task equally often overall and in a random sequence. The question was whether participants would avoid performing a task that they had recently switched away from (e.g., the task performed on trial n22), because the task set was still inhibited. Results confirmed that participants strongly avoided performing the n22 task (e.g., ABA) in favor of performing other tasks (e.g., ABC). This occurred both when participants were required to switch tasks every trial (Experiment 1) and when they were allowed to repeat tasks (Experiment 2). The results suggest that a task set is inhibited during switching to a new task, reducing the likelihood that this task will be selected in the near future.     

Cue enhancement as a function of task set

The hypothesis was tested that the intention to use a particular cue relation would enhance the effectiveness of that particular cue in determining the resulting perception. For this purpose, a situation was presented in which the apparent depth position of an object in a configuration of objects would differ depending upon which of two possible cue relations (size cues) were used. The results support the conclusion that the perceived depth position of the object differed in the expected directions as a function of the task set. The data of the study are discussed with respect to the “adjacency principle” which states that cue efficiency is determined by the relative adjacency of objects between which the cues occur. Although the effect of cue set upon the perception seems to be small compared with that of adjacency, it cannot completely be ignored.     

Task selection cost asymmetry without task switching

The switch cost asymmetry (i.e., larger costs when switching from a nondominant into a dominant task than vice versa) has been explained in terms of the trial-to-trial carryover of activation levels required for the dominant versus the nondominant task. However, there is an open question about whether an actual switch in task is in fact necessary to obtain a “selection” cost asymmetry. In Experiments 1 and 2, we modified an alternatingruns paradigm to include either long or short response-to-stimulus intervals (RSIs) after each pair of trials (i.e., AA-AA-BB-BB), thereby inducing selection costs not only at the point of a task switch (i.e., AA-BB), but also between same-task pairs (i.e., AA-AA). Using spatially compatible versus incompatible response rules (Experiment 1) and Stroop word versus color naming (Experiment 2), we found asymmetric effects not only at task-change transitions, but also at task-repeat transitions when the RSI was long (presumably inducing frequent losses of set). In Experiments 3A and 3B, a cost asymmetry for long RSIs was obtained even when competing tasks were separated into alternating single task blocks, but not when the tasks were compared in a betweensubjects design. This general pattern cannot be explained by activation carryover models, but is consistent with the idea that the asymmetry arises as a result of interference from long-term memory traces.     

Implicit sequence learning based on instructed task set

How does the way we code and control actions influence automatic skill acquisition processes? Wenke and Frensch (2005) showed that instructions can lead participants to code spatial responses based on color. Here, we tested in 3 experiments to what extent response labeling and instruction-based response coding can determine what is learned in implicit sequence learning. Instructions mapped 4 gray shape stimuli to 1 of the 4 keys each in a serial reaction task, referring to the keys in terms of either their color or their spatial location. In Experiments 1 and 2 we found that people in the color instruction conditions used color for action control and acquired sequence knowledge containing color: They were susceptible to irrelevant stimulus colors at transfer and could transfer color sequence knowledge to a new arrangement of response positions and fingers, whereas participants who had received spatial instructions could not. Implicit sequence learning was thus surprisingly flexible. Depending on whether an arbitrary nonspatial response feature was used or not used to explain the stimulus-response mappings, we either found or did not find evidence that this feature became part of action control and sequence learning. Furthermore, Experiment 3 suggested that response position might become part of the sequence knowledge even if instructions do not emphasize this response feature. Together, the findings suggest that implicit sequence learning is based on action control, which in turn strongly, but not entirely, depends on which response features are used to explain the stimulus-response mappings in the instructions. (PsycINFO Database Record (c) 2012 APA, all rights reserved).