Verbal representation in task order control: An examination with transition and task cues in random task switching

Recent task-switching studies in which a predictable task sequence has been used have indicated that verbal representation contributes to the control of task order information. The present study focused on the role of verbal representation in sequential task decisions, which are an important part of task order control, and examined the effects of articulatory suppression in a random-task-cuing paradigm with two different types of cues presented just before the presentation of a stimulus: a transition cue and a task cue. The former cue provided information only about switching or repeating the task, whereas the latter was associated directly with the identity of the task (i.e., indicating a parity or a magnitude task). In Experiment 1, in which transition cues guided task sequences, articulatory suppression impaired performance in both repetition and switch trials, thereby increasing the mixing costs. In Experiment 2, in which a task cue, rather than a transition cue, was presented to examine the influence of a cue-decoding process, articulatory suppression had no specific effect on task performance. Experiment 3, in which the transition cue and the task cue were randomly presented in the same block to equalize the memory load and task strategy for the two types of cues, confirmed that articulatory suppression significantly increased the mixing costs only in transition cue trials. The results from the three experiments indicated that the use of verbal representation is effective in sequential task decision—that is, in selecting a task set on the basis of transient task order information in both repetition and switch trials.     

Task-set switching and long-term memory retrieval

The authors tested the hypothesis of a close relationship between the intentional component of task-set switching ("advance reconfiguration;" R. D. Rogers & S. Monsell, 1995) and long-term memory (LTM) retrieval. Consistent with this hypothesis, switch costs are reported to be larger when the switched-to task involves high retrieval demands (i.e., retrieval of episodic information) than when it involves low retrieval demands (i.e., retrieval of semantic information). In contrast, switch costs were not affected by a primary-task difficulty manipulation unrelated to intentional retrieval demands (Experiment 2). Also, the retrieval-demand effect on switch costs was eliminated when time for advanced preparation or task cues explicitly specifying the task rules were provided (Experiment 3). Overall, results were consistent with the hypothesis that the intentional switch-cost component reflects the time demands of retrieving appropriate task rules from LTM.     

Unconscious activation of task sets

Using an explicit task cuing paradigm, we tested whether masked cues can trigger task-set activation, which would suggest that unconsciously presented stimuli can impact cognitive control processes. Based on a critical assessment of previous findings on the priming of task-set activation, we present two experiments with a new method to approach this subject. Instead of using a prime, we varied the visibility of the cue. These cues either directly signaled particular tasks in Experiment 1, or certain task transitions (i.e., task repetitions or switches) in Experiment 2. While both masked task and transition cues affected task choice, only task cues affected the speed of task performance. This observation suggests that task-specific stimulus–response rules can be activated only by masked cues that are uniquely associated with a particular task. Taken together, these results demonstrate that unconsciously presented stimuli have the power to activate corresponding task sets.     

Methodological and empirical issues when dissociating cue-related from task-related processes in the explicit task-cuing procedure

In the explicit cuing version of the task-switching paradigm, each individual task is indicated by a unique task cue. Consequently, a task switch is accompanied by a cue switch. Recently, it has been proposed that priming of cue encoding contributes to the empirically observed switch costs. This proposal was experimentally supported by using a 2:1 mapping of cues to tasks, so that a cue switch does not necessarily imply a task switch. The results indeed suggested a substantial contribution of “cue-switch costs” to task-switch costs. Here we argue that the 2:1 mapping potentially leads to an underestimation of “pure” task-switch costs. To support this argument, we report the results of a new study in which we used “transition cues” that indicate the identity of the current task based on the identity of the preceding task. This new type of cue allows a full factorial manipulation of cue switches and task switches because it includes the condition in which a cue repetition can also indicate a task switch (i.e., when the “switch” cue is repeated). We discuss the methodological implications and argue that the present approach has merits relative to the previously used 2:1 mapping of cues to tasks.     

Inner speech as a retrieval aid for task goals: the effects of cue type and articulatory suppression in the random task cuing paradigm

Articulatory suppression has been shown to increase switch costs in the list paradigm (e.g., [J. Exp. Psychol.: General 130 (2001) 641, J Memory Language 48 (2003) 148]). The present dual-task study examined whether this effect generalizes to the random task cuing paradigm. Participants performed color or shape judgments according to explicit word cues (COLOR or SHAPE) or less transparent letter cues ( C for the color task and S for the shape task). In the word cue condition, the switch cost was equivalent for the articulatory suppression and the control (no dual-task) conditions, but, in the letter cue condition, the switch cost was significantly greater for the articulatory suppression condition than for the control condition. These results suggest that inner speech may be recruited as a tool for retrieving and activating the relevant task goal when the task cue is not transparent and hence imposes nonnegligible retrieval demand.     

Individual differences in cognitive-flexibility: the influence of spontaneous eyeblink rate, trait psychoticism and working memory on attentional set-shifting

Individual differences in psychophysiological function have been shown to influence the balance between flexibility and distractibility during attentional set-shifting [e.g., Dreisbach et al. (2005). Dopamine and cognitive control: The influence of spontaneous eyeblink rate and dopamine gene polymorphisms on perseveration and distractibility. Behavioral Neuroscience, 119(2), 483-490]. Here we replicate both the facilitatory and detrimental influence of spontaneous eyeblink rate upon switch costs across the two distinct conditions of a set-shifting task. We extend this by presenting additional, putatively dopamine related, individual differences that also influence attentional control. Whereas trait psychoticism showed a pattern of effects opposite to that of eyeblink rate, greater working memory served to decrease switch costs across both conditions. These results highlight the need for further exploration of the role of dopaminergic neurotransmission and component processes involved in such attentional paradigms, and illustrates the importance of considering individual differences in cognitive control.     

The influence of cue unreliability on judgment in a multiple cue probability learning task

The effect of cue reliability was tested in a two-cue multiple-cue probability learning (MCPL) task. Subjects were 42 undergraduates. The cue validities were.78 and.37. Unreliability in a cue was defined as variability in multiple observations of that cue on a given trial. That variability was provided by adding random errors to the true value of the cue. One group was given consistent cues (i.e., the more valid cue was the more reliable cue), one group was given inconsistent cues, and the control group was given true scores. Cue reliability did not affect subjects' consistency or achievement, but did interact with the presence of outcome feedback. The subjective weights showed that subjects thought they weighted the more reliable cue more heavily regardless of the cue validities or their actual cue weightings. There were wide individual differences in performance, illustrating the need for an idiographic-statistical approach in studying decision making.     

Perseverative behavior and adaptive control in older adults: performance monitoring,rule induction,and set shifting

Older adults, like patients with dorsolateral frontal lobe lesions, have been shown to be progressively susceptible to errors of perseveration in the Wisconsin Card Sorting Test (WCST). This deficit may result from several types of endogenous adaptive control abilities. First, to enable behavioral modifications in response to sudden changes in task demands, one has to consider and evaluate the possible alternative categorization rules and select one for further testing (rule induction). Second, to perform the required shift appropriately, one should suppress the no-longer relevant task set and replace it by an appropriate new one (set shifting). Third, however, proper application of rule-induction and set-shifting abilities requires the ability to monitor and interpret task cues and feedback signals appropriately to guide behavior and to recognize the need to apply rule-shift operations (performance monitoring). To explore the extent to which these different endogenous adaptive control abilities are differentially sensitive to the effect of aging, young and older adults were tested in two experiments using WCST-like tasks. From the finding that older adults were not able to capitalize on explicit shift cues (either nonspecific or specific) the inference can be drawn that basic set-shifting abilities, rather than rule-induction or performance-monitoring abilities, were the primary factor responsible for the increased tendency to perseverate as adults grow into senescence.     

No-go trials can modulate switch cost by interfering with effects of task preparation

It has recently been shown that the cost associated with switching tasks is eliminated following ‘no-go’ trials, in which response selection is not completed, suggesting that the switch cost depends on response selection. However, no-go trials may also affect switch costs by interfering with the effects of task preparation that precede response selection. To test this hypothesis we evaluated switch costs following standard go trials with those following two types of non-response trials: no-go trials, for which a stimulus is presented that indicates no response should be made (Experiment 1); and cue-only trials in which no stimulus is presented following the task cue (Experiment 2). We hypothesized that eliminating no-go stimuli would reveal effects of task preparation on the switch cost in cue-only trials. We found no switch cost following no-go trials (Experiment 1), but a reliable switch cost in cue-only trials (i.e., when no-go stimuli were removed; Experiment 2). We conclude that no-go trials can modulate the switch cost, independent of their effect on response selection, by interfering with task preparation, and that the effects of task preparation on switch cost are more directly assessed by cue-only trials.     

Effects of execution duration on within-item strategy switching in young and older adults

This study aimed at determining whether previously found age-related differences in within-item strategy switching is modulated by duration of engagement in initial strategy execution. In a computational estimation task, young and older adults had to find estimates to arithmetic problems like 37×64 while either rounding down (i.e., 30×60) or rounding up (i.e., 40×70) both operands to the closest decades. Participants were asked to execute a cued strategy for different durations (i.e., 1, 2, or 3 s), before deciding whether the cued strategy was the best strategy and to switch to the best strategy if the cued strategy was not the best. The main findings revealed that (1) young and older adults were able to switch strategies, especially when they started to execute poorer strategy on a given item; (2) older adults switched strategy less often than young adults, and (3) both young and older participants switched strategy less frequently for long than for short durations. These findings suggest that to be able to switch strategy within item, participants should not be too much engaged in execution of the initially selected strategy, and that duration of engagement in initial strategy execution does not modulate age-related differences in within-item strategy execution.     

Task switching: the effect of task recency with dual- and single-affordance stimuli

When we switch to a new task, performance is transiently relatively poor, but improves dramatically after one trial. Such a “switch cost” may result from the preceding task being highly primed while the new task is not yet primed. This predicts that it should become more difficult to switch back to Task A when more trials of Task B have intervened. Such a lag effect has been found in some but not in most previous experiments, and to resolve this discrepancy we examined the effects of task lag with different stimuli. We found that when stimuli uniquely and clearly cued the task—minimizing the need for control—switch reaction time increased with task lag. However, when the need for control was increased by using similar or identical stimuli in the two tasks, this lag effect was abolished or reversed. Thus only when control processes are minimized can priming explain the difficulty of switching back from Task B to Task A. Second, we asked how the impact of control is mediated in conditions where it is not minimized. If it is mediated through altering the relative activation states of competing tasks, then as it becomes easier to do one task—the relative task-set activation state is tipped in that task's favour—it should always become harder to do the other task. On the other hand, if control bias affects switch performance directly, this relationship need not hold. We found that as it becomes easier to perform one task it can become easier, not harder, to switch to the competing task. Thus control bias must act directly on switch performance, rather than only through its influence on relative task-set activation.     

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.     

Exploring temporal dissipation of attention settings in auditory task switching

Using a cued auditory task-switching variant of dichotic listening, we varied the response–cue interval (RCI) to examine temporal dissipation effects. On each trial, participants were presented with two different number words, one spoken by a female speaker and another by a male speaker (dichotic listening), that served as competing targets for a numerical judgment. The gender of the task-relevant speaker was indicated by a visual task cue prior to each trial. Experiment 1A used two different cues for each task (i.e., gender) and showed only small cue repetition benefits (same cue vs. alternate cue) but large auditory switch costs (alternate cue vs. task switch). A replication without immediate cue repetitions (Experiment 1B) showed very similar switch costs, suggesting that immediate cue repetitions play a negligible role for the size of auditory task switch costs. Moreover, switch costs were reduced when the (entirely task-irrelevant) location of the task-relevant speaker changed, relative to when it was unchanged, suggesting an episodic feature-binding component in our dichotic-listening task. Importantly, both experiments showed no effect of RCI on auditory switch costs. Because statistical power for this null effect was reasonably high across experiments (n?=?50), this finding suggests that auditory attention settings do not dissipate quickly over time.     

Trading off switch costs and stimulus availability benefits: An investigation of voluntary task-switching behavior in a predictable dynamic multitasking environment

In the present study, we introduce a novel, self-organized task-switching paradigm that can be used to study more directly the determinants of switching. Instead of instructing participants to randomly switch between tasks, as in the classic voluntary task-switching paradigm (Arrington & Logan, 2004), we instructed participants to optimize their task performance in a voluntary task-switching environment in which the stimulus associated with the previously selected task appeared in each trial after a delay. Importantly, the stimulus onset asynchrony (SOA) increased further with each additional repetition of this task, whereas the stimulus needed for a task switch was always immediately available. We conducted two experiments with different SOA increments (i.e., Exp. 1a = 50 ms, Exp. 1b = 33 ms) to see whether this procedure would induce switching behavior, and we explored how people trade off switch costs against the increasing availability of the stimulus needed for a task repetition. We observed that participants adapted their behavior to the different task environments (i.e., SOA increments) and that participants switched tasks when the SOA in task switches approximately matched the switch costs. Moreover, correlational analyses indicated relations between individual switch costs and individual switch rates across participants. Together, these results demonstrate that participants were sensitive to the increased availability of switch stimuli in deciding whether to switch or to repeat, which in turn demonstrates flexible adaptive task selection behavior. We suggest that performance limitations in task switching interact with the task environment to influence switching behavior.     

Managing Sequential Task Portfolios in the Face of Temporal Atypicality and Task Complexity

The authors use a portfolio of sequential tasks to investigate how accurately study participants stick to assigned deadlines when they need to transition from one task to another. Atypical deadlines, task complexity, and individual differences all affect transition error size, error correction, and task performance. In Experiment 1 (N?=?108), larger task transition errors were related negatively to task performance and were associated with atypical deadlines (e.g., 4:53 or 4:57), complex tasks, and individuals lower in the general hurry characteristic. In Experiment 2 (N?=?95), individuals facing atypical deadlines or lower in need for cognition were less likely to correct transition errors (i.e., getting back to the original schedule), which negatively affected performance. Theoretical and practical implications are discussed.     

Not just semantics: Strong frequency and weak cognate effects on semantic association in bilinguals

To investigate the possibility that knowledge of two languages influences the nature of semantic representations, bilinguals and monolinguals were compared in a word association task. In Experiment 1, bilinguals produced less typical responses relative to monolinguals when given cues with a very common associate (e.g., given bride, bilinguals said “dress” instead of “groom”). In Experiment 2, bilinguals produced responses as typical as those of monolinguals when given cues with high-frequency associates, but not when given cues with lowfrequency associates. Bilinguals’ responses were also affected, to a certain extent, by the cognate status of the stimulus word pairs: They were more similar to monolinguals’ responses when the cue and its strongest associate were both cognates (e.g., minute-second is minuto-segundo in Spanish), as opposed to both being noncognates. Experiment 3 confirmed the presence of a robust frequency effect on bilingual but not on monolingual association responses. These findings imply a lexical locus for the bilingual effect on association responses and reveal the association task to be not quite as purely semantic as was previously assumed.     

The basic laws of conditioning differ for elemental cues and cues trained in compound

The cue-duration effect (i.e., longer cues result in less conditioned responding than shorter cues) was examined as a function of whether cues were trained alone or in compound. Compound (AX) or elemental (X) cues of either long or short duration were paired with the unconditioned stimulus. In testing with X alone, the cue-duration effect was observed with elementally trained cues, but not with compound cues. Instead, stronger responding resulted from training with long compound cues relative to short compound cues (i.e., a reversed cue-duration effect). Moreover, an overshadowing effect (i.e., decreased responding due to compound conditioning) was observed when conditioning was conducted with a short cue, but compound conditioning resulted in enhanced responding when it was conducted with a long cue (i.e., reversed overshadowing). These findings are consistent with other recent demonstrations that some laws of learning that apply to elementally trained cues do not similarly apply to cues trained in compound.     

Task switching: The effect of task recency with dual- and single-affordance stimuli

When we switch to a new task, performance is transiently relatively poor, but improves dramatically after one trial. Such a “switch cost” may result from the preceding task being highly primed while the new task is not yet primed. This predicts that it should become more difficult to switch back to Task A when more trials of Task B have intervened. Such a lag effect has been found in some but not in most previous experiments, and to resolve this discrepancy we examined the effects of task lag with different stimuli. We found that when stimuli uniquely and clearly cued the task—minimizing the need for control—switch reaction time increased with task lag. However, when the need for control was increased by using similar or identical stimuli in the two tasks, this lag effect was abolished or reversed. Thus only when control processes are minimized can priming explain the difficulty of switching back from Task B to Task A. Second, we asked how the impact of control is mediated in conditions where it is not minimized. If it is mediated through altering the relative activation states of competing tasks, then as it becomes easier to do one task—the relative task-set activation state is tipped in that task's favour—it should always become harder to do the other task. On the other hand, if control bias affects switch performance directly, this relationship need not hold. We found that as it becomes easier to perform one task it can become easier, not harder, to switch to the competing task. Thus control bias must act directly on switch performance, rather than only through its influence on relative task-set activation.     

Dissociating the components of switch cost using two-to-two cue-task mapping

In the task switch paradigm, a switch of task is typically accompanied by a change in task cue. It has been proposed that the performance deficit usually observed when switching tasks is actually the result of changing cues. To test this possibility, we used a 2:2 cue-task mapping in which each cue indicated 2 different tasks. With advance presentation of a cue, the cost associated with changing cues disappeared, though a substantial task switch cost remained. Without advance cues, the relative contributions of task switch cost and cue change cost differed by transition frequencies. The results suggest that task execution contributes to switch cost independent of cue changes.     

Eye gaze cannot be ignored (but neither can arrows)

Recent studies have shown that switch costs (i.e., slower responding on task-alternation trials than on task-repetition trials) are not observed when on the preceding trial a no-go signal instructed the participant to withhold the response to the target stimulus. This finding suggests that neither task set is inhibited on no-go trials, and that the origin of switch costs is located in the application of the task set to the target stimulus. However, these studies also showed that responding after a no-go trial is substantially slower than after a go trial. This suggests that both task sets are inhibited on no-go trials and that switch costs originate from the preparation of a task set. In two experiments we created conditions that revealed an absence of switch costs in conjunction with relatively fast responding after no-go trials. Together these findings confirm that switch costs originate from the application of the task set.