Can time-based decay explain temporal distinctiveness effects in task switching?

In task switching, extending the response–cue interval (RCI) reduces the switch cost—the detriment to performance when switching compared to repeating tasks. This reduction has been used as evidence for the existence of task-set decay processes. Recently, this has been challenged by the observation of sequential dependencies on the RCI effect: switch cost is only reduced at longer RCIs when the previous trial had a short RCI. This trial-wise variation of RCI is thought to affect the temporal distinctiveness (TD) of a previous task's episodic trace, affecting the probability of its automatic retrieval on the current trial; importantly, TD is thought to be independent of the current trial's RCI. The present study highlights a dependency between the current RCI and TD, and demonstrates that a decay model can reproduce some patterns of data attributed to TD. Further, the decay account makes a strong prediction when TD is held constant: repetition response times should slow as the RCI increases, and switch response times should be facilitated. This prediction was tested via re-analysis of extant data and three experiments. The re-analysis provided some evidence for the decay account, but Experiments 1 and 2 report slowing for task repetition and switch trials, which cannot be explained by a task-set decay process. Experiment 3, which utilized tasks requiring perceptual judgements, showed small evidence for decay. We conclude that the data are largely consistent with the TD account and that the evidence for decay of higher-level task-sets is not convincing.     

Repetition priming in task switching: Do the benefits dissipate?

In task-switching research, one process that has been implicated as a possible source of switch cost is repetition priming. In four experiments, an examination was made of the claim that repetition priming dissipates over the interval between trials and thereby causes switch cost to decrease with increases in the response-cue interval (RCI). In Experiments 1 and 2, RCI was manipulated within participants, producing the standard RCI effect on switch cost. In Experiments3 and 4, RCI was manipulated between participants and had no effect on switch cost. The role of experimental design and the mixed pattern of effects on switch and repeat trials in Experiments1 and 2 suggest that a passive architectural process such as priming dissipation is not responsible for the RCI effect on switch cost. Repetition priming may still be responsible for some or all of switch cost, but it appears to be more stable over time than was previously thought.     

The coupling between spatial attention and other components of task-set: A task-switching investigation

Is spatial attention reconfigured independently of, or in tandem with, other task-set components when the task changes? We tracked the eyes of participants cued to perform one of three digit-classification tasks, each consistently associated with a distinct location. Previously we observed, on task switch trials, a substantial delay in orientation to the task-relevant location and tendency to fixate the location of the previously relevant task—“attentional inertia”. In the present experiments the cues specified (and instructions emphasized) the relevant location rather than the current task. In Experiment 1, with explicit spatial cues (arrows or spatial adverbs), the previously documented attentional handicaps all but disappeared, whilst the performance “switch cost” increased. Hence, attention can become decoupled from other aspects of task-set, but at a cost to the efficacy of task-set preparation. Experiment 2 used arbitrary single-letter cues with instructions and a training regime that encouraged participants to interpret the cue as indicating the relevant location rather than task. As in our previous experiments, and unlike in Experiment 1, we now observed clear switch-induced attentional delay and inertia, suggesting that the natural tendency is for spatial attention and task-set to be coupled and that only quasi-exogenous location cues decouple their reconfiguration.     

预先信息的不确定性与准备时间对任务切换的影响

为揭示任务切换中切换代价的本质, 考察了预先信息与准备时间对任务切换的影响, 结果发现: (1) 预先信息对任务切换有显著的影响效应, 全部信息的反应时和切换代价显著低于无信息和部分信息的反应时和切换代价, 而后二者之间无显著差异; (2) 预先信息的影响效应受到准备时间的调节作用, 在准备时间为100ms时, 预先信息无显著的影响效应, 而在准备时间达到600ms以后, 预先信息的准备效应显著。这说明, 预先信息影响的认知加工是任务设置重构, 并且这种影响效应受到准备时间的调节作用。     

任务切换机制研究的理论争议与整合

任务切换是执行控制的一种重要功能。切换代价是量化执行控制持续时间的指标。并广泛应用于各个研究领域。但是切换代价在多大程度上体现了执行控制的作用,仍然还存在争论．当前主要存在任务设置重构、任务设置惯性和联结竞争三种理论。本文首先介绍了三种理论的基本观点和实验证据,以及对任务切换加工机制的分析;其次阐明了对三种理论进行整合的相关研究;最后分析了进一步研究的方向。     

Intentional switching of auditory attention between long and short sequential tone patterns

The current study focuses on auditory task switching, more precisely on switching attention between different temporal patterns of the same auditory stimulus. Tone sequences consisting of nine different pitch tones were presented aurally. Three repetitive short 3-tone patterns (local focus) were combined to a long pattern (global focus), and each could be either rising or falling, resulting in congruent or incongruent combinations. Participants were informed by a cue if they had to attend to the short or to the long pattern, and they indicated if the target pattern was rising or falling by pressing one of two keys. In two experiments, we investigated cued switches between the two attentional foci. Switch costs in reaction times and errors were observed when switching from the long to the short pattern but not when switching from the short to the long pattern. These asymmetric switch costs were reduced when participants had more time to prepare for the switch in a condition with a prolonged cue-stimulus interval. In addition, participants made more errors when global and local patterns did not correspond to each other (i.e., in incongruent trials) when attending to either of the patterns, but this congruency effect was not modulated by preparation time. The data suggest that the mechanisms of task goal prioritizing, as indicated by the asymmetric attention switch costs, are dissociable from those underlying stimulus selection, as indicated by the congruency effects.     

Executive control in set switching: residual switch cost and task-set inhibition.

Executive processes necessary for flexibly switching between different tasks were studied using a set switching paradigm that requires participants to rapidly switch between different tasks across consecutive trials. Switch cost reflects poorer performance for task-switch trials than for consecutive same-task trials. Significant switch cost was observed even with considerable preparation time before a task-switch, an effect known as residual switch cost. This study tested the hypothesis that one process underlying residual switch cost is inhibition of the previous task-set. We used semantic categorization tasks to compare switch cost between alternating task series (ABA) and nonalternating series (ABC) in order to test the generality of a task-set inhibition effect previously observed with perceptual judgment tasks (Mayr & Keele, in press). The results yielded significant switch cost only for alternating tasks, in both response times and errors resulting from performance of the wrong task. Thus, resolving inhibition associated with previously abandoned task-sets may be the main process underlying residual switch costs, suggesting that task-set inhibition is an important executive control process.     

Automatic and intentional activation of task sets.

Four experiments examined automatic and intentional activation of task sets in a switching paradigm. Experiment 1 demonstrated incidental task sequence learning that was not accompanied by verbalizable task sequence knowledge. This learning did not affect task shift cost and may be attributed to automatic task-set activation. In Experiment 2, both shift cost and learning effect increased when the response-cue interval was short, indicating the influence of residual, persisting activation of the preceding task set. In Experiment 3, learning disappeared with a long cue-stimulus interval (CSI), which resulted in a strong preparation effect. This preparation, however, reduced reaction time level but was not specific to task shifts. Finally, Experiment 4 showed that a within-subject C     

任务切换中切换代价产生的机制

关于任务切换中切换代价的来源和本质,目前主要有三种观点:任务设置惯性、任务设置重构和联结竞争。为揭示三者的关系,研究了在不同延迟时间条件下,预先信息与刺激类型对切换代价的影响机制。结果发现:延迟时间、预先信息和刺激类型对切换代价均有显著的作用,但是,三者之间的二次和三次交互作用均不显著。这表明,切换代价反映了任务设置惯性、任务设置重构和联结竞争三种成分,并且三者的关系是具有可加性的序列认知加工。     

The effects of recent practice on task switching

Four experiments investigated the effect of recent selective practice on the cost of switching between 2 tasks afforded by letter-digit pairs: alphabet arithmetic and shape comparison. Experiments 1 and 2 found a greater cost associated with switching to the more recently practiced task: evidence that task-set inertia contributes to switching costs. Experiment 3 found this effect to be limited to trials on which a recently trained stimulus followed another such stimulus: a result problematic for all current theories of task-set priming. Experiment 4 showed that the effect of recent practice was eliminated by active preparation for a task switch: It appears that endogenous task-set preparation reduces the effects of task-set inertia. ((c) 2003 APA, all rights reserved)     

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.     

Generic cognitive adaptations to task interference in task switching

The present study investigated how the activation of previous tasks interferes with the execution of future tasks as a result of temporal manipulations. Color and shape matching tasks were organized in runs of two trials each. The tasks were specified by a cue presented before a task run, cueing only the first trials of each run. Response times (RTs) and error rates were measured for task switching and task repetition conditions. Task interference was varied as a function of response-cue interval (RCI of 300 and 900 ms), that is, the interval between the task runs. Keeping the response-stimulus interval within the task runs constant at 300 ms allowed the disentangling of the direct effects of RCI manipulation on performance (first trials) from the general effects on performance (both trials in the run). The data showed similar performance improvement due to RCI increase on both trials in the task run. Furthermore, increasing RCI improved both switch and repetition performance to a similar extent. Together, our findings provide further evidence for accounts stressing generic effects of proactive task interference in task switching.     

Asymmetric switch cost and backward inhibition: Carryover activation and inhibition in switching between tasks of unequal difficulty.

Asymmetric switch cost, observed when switching between tasks varying in difficulty, shows that the difference between repeat and switch trials is greater when switching to the easier task. Early explanations of this effect attributed this pattern to both positive priming of the difficult task and negative priming of the easier task, but more recent models have focused only on activation processes. The role of inhibition in asymmetric switch cost was examined using backward inhibition, a more direct measure of task-set inhibition. The results indicated asymmetric backward inhibition, with greater sequential inhibition of the easier task (i.e., easy-difficult-easy sequences). Switch costs, however, showed both typical and reversed asymmetry (greater cost when switching from the easy to the difficult task), depending on the relative difficulty of task pairs. This pattern of results indicates that switch costs are attributable to both activation and inhibition processes.     

Flanker compatibility effects in patients with Parkinson's disease: impact of target onset delay and trial-by-trial stimulus variation

Parkinson’s disease (PD) patients and healthy controls were administered a flanker task that consisted of the presentation of colored targets and distractors. Participants were required to attend to the center target and identify its color. The stimulus displays were either congruent (i.e., the target and flankers were the same color) or incongruent. The time between the onset of the flanker and the target color (the target onset delay) was either short or long. Results indicated that PD patients and controls did not differ in the magnitude of the flanker effect within individual trials in that both groups demonstrated a typical flanker effect at the short target onset delay and neither group demonstrated a flanker effect at the longer delay. However, when performance was examined on a trial-by-trial basis, PD patients demonstrated a slowing of reaction time relative to controls when having to make the same response across consecutive trials at longer inter-trial intervals when the flankers were incongruent across consecutive trials and the display on the second of two trials was incongruent. These results indicate that PD patients are impaired in inhibiting the distractors over an extended delay and that this deficit may impact motor responding in these patients, suggesting that the basal ganglia contribute to the interface of attention and action.     

任务切换理论争议新证据

任务切换是研究认知控制的主要范式之一。大量研究发现切换试次比重复试次的反应时更长,错误率更高,这种差异称为切换代价。任务切换时所产生切换代价的理论解释主要有惯性论、重构论和联结论。近十年来,这些理论均获得新的实验支持和发展,但其争议依旧,没有哪一理论能成功解释任务切换的所有效应。未来研究可以建立整合模型,以准确描述切换代价产生的认知机制。     

Total sleep deprivation increases the costs of shifting between simple cognitive tasks

In two experiments we studied the effects of one night of total sleep deprivation on task-shift costs. In different conditions shifts were between types of judgment (extradimensional shifts) and between stimulus-response mappings (intradimensional shifts). In addition, with an alternating-runs procedure we used short and long response-to-stimulus intervals and also external precues to vary the opportunities for advance configuration of task sets. Under all conditions sleep deprivation increased shift costs derived from the 20% slowest reaction times, which were insensitive to the opportunities for advance configuration. Shift costs derived from the 20% fastest reaction times were increased only for extradimensional shifts. As indicated by congruency effects, the increase of shift costs after a night without sleep cannot be attributed to increased interference between competing task sets. The findings suggest that total sleep deprivation increases task-set instability and thus lapsing, in particular in conditions with long stimulus-to-response intervals and in shift trials. In addition total sleep deprivation seems to increase the duration of an exogenously controlled process involved in extradimensional shifts.     

Automatic attentional orienting to other people’s gaze in schizophrenia

Explicit tests of social cognition have revealed pervasive deficits in schizophrenia. Less is known of automatic social cognition in schizophrenia. We used a spatial orienting task to investigate automatic shifts of attention cued by another person’s eye gaze in 29 patients and 28 controls. Central photographic images of a face with eyes shifted left or right, or looking straight ahead, preceded targets that appeared left or right of the cue. To examine automatic effects, cue direction was non-predictive of target location. Cue–target intervals were 100, 300, and 800?ms. In non-social control trials, arrows replaced eye-gaze cues. Both groups showed automatic attentional orienting indexed by faster reaction times (RTs) when arrows were congruent with target location across all cue–target intervals. Similar congruency effects were seen for eye-shift cues at 300 and 800?ms intervals, but patients showed significantly larger congruency effects at 800?ms, which were driven by delayed responses to incongruent target locations. At short 100-ms cue–target intervals, neither group showed faster RTs for congruent than for incongruent eye-shift cues, but patients were significantly slower to detect targets after direct-gaze cues. These findings conflict with previous studies using schematic line drawings of eye-shifts that have found automatic attentional orienting to be reduced in schizophrenia. Instead, our data indicate that patients display abnormalities in responding to gaze direction at various stages of gaze processing—reflected by a stronger preferential capture of attention by another person’s direct eye contact at initial stages of gaze processing and difficulties disengaging from a gazed-at location once shared attention is established.     

Joint task switching

The present study investigates the representation of task-sets in a joint dual-task setting. To this end, a task-switching approach is used. Task switching is associated with a switch cost, which can be decomposed in several markers of task-set coordination. These markers can be used to investigate whether participants represent the co-actor's task-set in a joint dual-task setting. A joint task-switching procedure was used in which two participants performed a distinct task and the participants’ turn to respond could switch or repeat on a trial-by-trial basis. The results indicate that joint task switching also elicits a switch cost. However, this switch cost does not seem to be related to the representation of the co-actor's task-set. It is suggested that the switch cost observed in joint task switching is based on processes of task monitoring, which increase the saliency of task-irrelevant stimulus information.     

Task switching and the measurement of “switch costs”

The measurement of “switch costs” is held to be of interest because, as is widely believed, they may reflect the control processes that are engaged when subjects switch between two (or more) competing tasks. [In task-switching experiments, the reaction time (RT) switch cost is typically measured as the difference in RT between switch and non-switch (repeat) trials.] In this report we focus on the RT switch costs that remain even after the subject has had some time to prepare for the shift of task, when the switch cost may be approximately asymptotic (so-called residual switch costs). Three experiments are presented. All three experiments used Stroop colour/word, and neutral stimuli. Participants performed the two tasks of word-reading and colour-naming in a regular, double alternation, using the “alternating runs” paradigm (R. D. Rogers & S. Monsell, 1995). The experiments were designed to test the hypothesis that RT switch costs depend on a form of proactive interference (PI) arising from the performance of a prior, competing task. A. Allport, E. A. Styles and S. Hsieh (1994) suggested that these PI effects resulted from “task-set inertia”, that is, the persisting activation-suppression of competing task-sets, or competing task-processing pathways. The results confirmed the existence of long-lasting PI from the competing task as a major contributor to switch costs. Non-switch trials, used as the baseline in the measurement of switch costs, were also shown to be strongly affected by similar PI effects. However, task-set inertia was not sufficient to account for these results. The results appeared inconsistent also with all other previous models of task switching. A new hypothesis to explain these between-task interference effects was developed, based on the stimulus-triggered retrieval of competing stimulus-response (S-R) associations, acquired (or strengthened) in earlier trials. Consistent with this retrieval hypothesis, switch costs were shown to depend primarily on the S-R characteristics of the preceding task (the task that was switched from) rather than the upcoming task. Further, the effects of the other, competing task were found to persist over many successive switching trials, affecting switch costs long after the stimulus overlap (and hence the principal S-R competition) between the current tasks had been removed. Switch costs were also found to be affected by recent, item-specific experience with a given stimulus, in either the same or the competing task. Finally, the results showed that switch costs were massively affected by the ratio of the number of prior trials, in response to the same stimuli, that had implemented either the currently intended or the competing S-R mappings. None of these effects are predicted by current models of residual switch costs, which appeal to the differences in control processes assumed to be engaged in switch versus non-switch trials. Received: 31 March 1999 / Accepted: 23 July 1999     

刺激类型与预先信息对任务切换的影响

为揭示联结竞争与任务设置重构在切换加工过程中的关系,以切换代价为指标,研究了刺激类型与预先信息对任务切换的影响效应,结果发现:(1)无信息的切换代价显著高于部分信息和全部信息的切换代价,而后二者之间无显著差异;(2)单向刺激的切换代价显著高于双向刺激的切换代价;(3)预先信息和刺激类型对切换代价的影响无交互作用。这表明任务设置重构与联结竞争是两个具有相加效应的序列认知活动。