Task preparation based on precues versus memory: Precues lead to superior performance with two tasks but not with four tasks

There is considerable evidence that task switching proceeds more efficiently with preparation based on explicit precues than on the basis of a learned sequence of tasks. However, this evidence stems almost exclusively from experiments in which participants switched between only two tasks. In two experiments stronger preparation effects with explicit precues compared to memory-based preparation was replicated with two tasks. With four tasks, however, preparation based on memory was at least as efficient as preparation based on precues. A third experiment ruled out the possibility that this latter finding was due to increased difficulty of cue processing with two-dimensional cues. These findings question the generalisability of observations regarding preparation effects that are based on two-task situations. It is suggested that one crucial factor regarding the relative efficiency of precue-based and memory-based preparation pertains to the fact that with two tasks, the relevant task can be determined by knowing only the previous task and whether a switch is required or not. This is not possible with four tasks that require a more elaborated task representation at the outset, which in turn may be more apt to support memory-based preparation.     

Preparation for a forthcoming task is sufficient to produce subsequent shift costs

Shifting from one task to another is associated with significant costs. Recently, it has been questioned whether the mere preparation for a forthcoming task, without the task’s actually being executed, is sufficient to establish a new task set that results in shift costs when the execution of a task other than the prepared task is required. In a go/no-go study, it is shown that the mere preparation for a task is sufficient to produce shift costs, but only under conditions that encourage participants to engage in advance preparation for a precued task despite the possibility that the execution of this task will not always be required, because of occasional no-go trials. In addition, considerable reductions of shift costs after go trials could be observed under these conditions. When such a motivating context was not provided, only negligible shift costs were observed after a no-go trial, indicating that no task-set configuration had taken place without the need to perform the task. Furthermore, under these conditions, prolonging the preparation interval resulted in reaction time benefits that were similar for task shifts and repetitions, again indicating that no active task-set configuration took place.     

Performing the unexplainable: Implicit task performance reveals individually reliable sequence learning without explicit knowledge

Memory-impaired patients express intact implicit perceptual-motor sequence learning, but it has been difficult to obtain a similarly clear dissociation in healthy participants. When explicit memory is intact, participants acquire some explicit knowledge and performance improvements from implicit learning may be subtle. Therefore, it is difficult to determine whether performance exceeds what could be expected on the basis of the concomitant explicit knowledge. Using a challenging new sequence-learning task, robust implicit learning was found in healthy participants with virtually no associated explicit knowledge. Participants trained on a repeating sequence that was selected randomly from a set of five. On a performance test of all five sequences, performance was best on the trained sequence, and two-thirds of the participants exhibited individually reliable improvement (by chi-square analysis). Participants could not reliably indicate which sequence had been trained by either recognition or recall. Only by expressing their knowledge via performance were participants able to indicate which sequence they had learned.     

Retention of Implicit Sequence Learning in Persons Who Stutter and Persons With Parkinson's Disease

ABSTRACT. The authors investigated the retention of implicit sequence learning in 14 persons with Parkinson's disease (PPD), 14 persons who stutter (PWS), and 14 control participants. Participants completed a nonsense syllable serial reaction time task in a 120-min session. Participants named aloud 4 syllables in response to 4 visual stimuli. The syllables formed a repeating 8-item sequence not made known to participants. After 1 week, participants completed a 60-min retention session that included an explicit learning questionnaire and a sequence generation task. PPD showed retention of general learning equivalent to controls but PWS's reaction times were significantly slower on early trials of the retention test relative to other groups. Controls showed implicit learning during the initial session that was retained on the retention test. In contrast, PPD and PWS did not demonstrate significant implicit learning until the retention test suggesting intact, but delayed, learning and retention of implicit sequencing skills. All groups demonstrated similar limited explicit sequence knowledge. Performance differences between PWS and PPD relative to controls during the initial session and on early retention trials indicated possible dysfunction of the cortico-striato-thalamo-cortical loop. The etiological implications for stuttering, and clinical implications for both populations, of this dysfunction are discussed.     

You can't always get what you want: The influence of unexpected task constraint on voluntary task switching

The current study assessed the effect that unexpected task constraint, following self-generated task choice, has on task switching performance. Participants performed a modified double-registration voluntary task switching procedure in which participants specified the task they wanted to perform, were presented with a cue that, on the majority of trials, confirmed the choice, and then performed the cued task. On a small portion of trials, participants were cued to perform a task that did not match their choice. Trials on which cues unexpectedly failed to match the chosen task were associated with costs. These costs were particularly large when participants chose to switch tasks but had to unexpectedly repeat the previous task. The results suggest that when participants choose to switch tasks, they prepare for that switch in anticipation of the stimulus, and the preparation is durable such that it cannot be readily undone.     

Spatial interference and response control in sequence learning: the role of explicit knowledge

In several sequence learning studies it has been suggested that response control shifts from the stimuli to some internal representation (i.e., motor program) through the learning process. The main questions addressed in this paper are whether this control shift is related to explicit knowledge and whether the formation of these internal representations depends on the stimulus attributes. In one experiment we compared the learning of a response sequence triggered by either spatial location or location symbol (left-right) by using a serial response task (SRT). Symbols were presented at either a centered or random location. The results showed that in the symbolic conditions the shift of response control correlated with the emergence of explicit knowledge. Only participants with complete explicit knowledge seemed to learn the sequence structure beyond probabilistic information (response time "RT" did not depend on the frequency of the response). Moreover, these participants were able to overcome, when needed, spatial interference (RT was the same for both spatially corresponding and non-corresponding trials). However, when spatial location was relevant, RT was always faster, especially for more frequent responses. These results suggest that the relevant stimulus dimension (location or symbol) seems to engage different sequence learning mechanisms.     

Cognitive control under stress: how stress affects strategies of task-set reconfiguration

This study investigated the effect of stress on cognitive control in task shifting. Subjects shifted between two tasks in an explicit cuing paradigm. Shift costs (i.e., performance decrements on task shifts relative to task repetitions) were measured for a long and a short cue-stimulus interval (CSI). Stress was varied by administering low-stress and high-stress IQ scales to two groups of subjects. In the low-stress group, shift costs were reduced with an increased CSI, a result that typically indicates anticipatory and shift-specific task-set reconfiguration. In the high-stress group, however, shift costs were independent of the CSI. This result is consistent with the idea that stress induces a change in the reconfiguration strategy, possibly to adapt to depleted resources.     

Implicit learning of sequences of tasks

Task sets can be configured in advance of performing a new task. However, the degree to which advance information is actually used for advance configuration depends on the nature of the available information. The role of implicit learning was explored in 2 experiments by means of a modified serial reaction time task with repeated sequences of 4 dimensionally organized tasks. Although there was clear evidence for implicit learning of the sequence (of length 8), the learning was not associated with a reduction of shift costs, either with a short (200 ms) or with a long (1,200 ms) response-stimulus interval. In contrast, a reduction of shift costs was observed when external precues were introduced in a 3rd experiment. According to these results, the sequences of stimulus features that serve as cues for the tasks to perform on the stimuli are learned, but the representation of the features is void of their task-associated meanings.     

Effects of deviant trials on precue-based versus memory-based switching among two or four tasks

In two experiments, the effects of an introduction of deviant trials on precue-based and memory-based task switching were investigated. Deviant trials were trials that deviated from task foreknowledge as induced either by precues or memory of the task sequence. The experiments differed with respect to the number of tasks to be switched among (two in Experiment 1, four in Experiment 2). In Experiment 1, the introduction of deviant trials had a detrimental effect on precue-based task preparation, but had little impact on memory-based preparation. The latter observation was due to the fact that there was little evidence for memory-based preparation at the outset. In Experiment 2, introducing deviant trials had little effect on either precue-based or memory-based preparation. In contrast to Experiment 1, in Experiment 2 memory-based preparation was as effective as precue-based preparation.     

Chunking in task sequences modulates task inhibition

In a study of the formation of representations of task sequences and its influence on task inhibition, participants first performed tasks in a predictable sequence (e.g., ABACBC) and then performed the tasks in a random sequence. Half of the participants were explicitly instructed about the predictable sequence, whereas the other participants did not receive these instructions. Task-sequence learning was inferred from shorter reaction times (RTs) in predictable relative to random sequences. Persisting inhibition of competing tasks was indicated by increased RTs in n- 2 task repetitions (e.g., ABA) compared with n- 2 nonrepetitions (e.g., CBA). The results show task-sequence learning for both groups. However, task inhibition was reduced in predictable relative to random sequences among instructed-learning participants who formed an explicit representation of the task sequence, whereas sequence learning and task inhibition were independent in the noninstructed group. We hypothesize that the explicit instructions led to chunking of the task sequence, and that n- 2 repetitions served as chunk points (ABA-CBC), so that within-chunk facilitation modulated the inhibition effect.     

Attentional load and implicit sequence learning

A widely employed conceptualization of implicit learning hypothesizes that it makes minimal demands on attentional resources. This conjecture was investigated by comparing learning under single-task and dual-task conditions in the sequential reaction time (SRT) task. Participants learned probabilistic sequences, with dual-task participants additionally having to perform a counting task using stimuli that were targets in the SRT display. Both groups were then tested for sequence knowledge under single-task (Experiments 1 and 2) or dual-task (Experiment 3) conditions. Participants also completed a free generation task (Experiments 2 and 3) under inclusion or exclusion conditions to determine if sequence knowledge was conscious or unconscious in terms of its access to intentional control. The experiments revealed that the secondary task impaired sequence learning and that sequence knowledge was consciously accessible. These findings disconfirm both the notion that implicit learning is able to proceed normally under conditions of divided attention, and that the acquired knowledge is inaccessible to consciousness. A unitary framework for conceptualizing implicit and explicit learning is proposed.     

语音控制加工经验有助于促进语音执行控制功能

来自双语的研究表明,双语者在抑制、转换、注意力维持等执行控制功能方面较之于单语者具有显著的认知优势效应。该效应是双语者对诸多语言亚成分协同控制的结果,还是对不同语音体系控制的结果,目前依然存在争论。本研究以单语单言儿童（仅会说汉语普通话）和单语双言儿童（同时会使用汉语普通话和泰州方言）为被试,通过线索-切换任务和语音Stroop任务就上述问题进行了研究。结果显示：（1）在线索-切换任务上,两组儿童作业表现差异不显著;（2）在语音Stroop任务上,单语双言儿童具有显著的认知优势。据此,本研究认为双语认知优势的获得是个体对诸如句法、语义、正字法、语音、词素等多种语言亚成分协同控制的结果。     

Congruency sequence effect in cross-task context: Evidence for dimension-specific modulation

The congruency sequence effect refers to a reduced congruency effect after incongruent trials relative to congruent trials. This modulation is thought to be, at least in part, due to the control mechanisms resolving conflict. The present study examined the nature of the control mechanisms by having participants perform two different tasks in an alternating way. When participants performed horizontal and vertical Simon tasks in Experiment 1A, and horizontal and vertical spatial Stroop task in Experiment 1B, no congruency sequence effect was obtained between the task congruencies. When the Simon task and spatial Stroop task were performed with different response sets in Experiment 2, no congruency sequence effect was obtained. However, in Experiment 3, in which the participants performed the horizontal Simon and spatial Stroop tasks with an identical response set, a significant congruency sequence effect was obtained between the task congruencies. In Experiment 4, no congruency sequence effect was obtained when participants performed two tasks having different task-irrelevant dimensions with the identical response set. The findings suggest inhibitory processing between the task-irrelevant dimension and response mode after conflict.     

Anticipatory modulation of interference induced by unpleasant pictures

In a series of experiments participants were asked to make speeded judgments regarding the correctness of arithmetic equations (arithmetic verification task) that were presented in front of pictures that are assumed to elicit neutral, positive, or strong negative emotional responses. In some conditions, precues predicted the affective valence of the next picture, whereas in other conditions the precues were uncorrelated with the type of picture. The main question was in which way the opportunity to anticipate a forthcoming negatively valenced stimulus would modulate its impact on cognitive performance. Anticipation generally enhanced the interfering effect of unpleasant pictures. This effect was largely independent of the arousal induced by the pictures. The findings suggest that informative precues led participants to integrate the valence of the pictures into their task representation, which in the case of negative pictures resulted in a somewhat paradoxical intensification of emotional interference.     

The costs of suppressing stressful memories

We investigated the costs of suppressing emotional and nonemotional memories, as evidenced in response times on a concurrent sentence verification task with three levels of syntactic complexity. Participants suppressing memories of personal negative experiences (n=26) had slower response times compared to the control group (n=23) and to participants suppressing nonemotional memories (n=25) particularly on the most complex sentences. Participants suppressing nonpersonal negative experiences (n=26) did not differ from either of the other two suppression groups. Suppression failures did not differ between conditions, but failures during the sentence task were related to the intrusiveness of the memory being suppressed. The findings indicate that different kinds of memories have different suppression costs and that even successful thought suppression can impair performance on concurrent tasks, supporting Wegner's ironic processing model in which suppression attempts must compete with other ongoing tasks for scarce mental resources.     

Temporal binding during apparent movement of the human body

Alternating between static images of human bodies with an appropriate interstimulus interval (ISI) produces apparent biological motion. Here we investigate links between apparent biological motion and time perception. We presented two pictures of the initial and final positions of a human movement separated by six different ISIs. The shortest movement path between two positions was always biomechanically impossible. Participants performed two tasks: In an explicit task, participants judged whether they saw the longer, feasible movement path between the two postures, or the shorter, biomechanically impossible path. In an implicit task, participants judged the duration of a white square surrounding the picture sequence. At longer ISIs participants were more likely to see a longer, feasible movement path (explicit task) and underestimated the duration of body picture pairs, compared to trials displaying degraded body pictures (implicit task). We argue that perceiving apparent biological motion involves temporal binding of two static pictures into a continuous movement. Such temporal binding may be mediated by a top-down mechanism that produces a percept of biological motion in the absence of any retinal motion.     

The costs of crossing paths and switching tasks between audition and vision

Switching from one functional or cognitive operation to another is thought to rely on executive/control processes. The efficacy of these processes may depend on the extent of overlap between neural circuitry mediating the different tasks; more effective task preparation (and by extension smaller switch costs) is achieved when this overlap is small. We investigated the performance costs associated with switching tasks and/or switching sensory modalities. Participants discriminated either the identity or spatial location of objects that were presented either visually or acoustically. Switch costs between tasks were significantly smaller when the sensory modality of the task switched versus when it repeated. This was the case irrespective of whether the pre-trial cue informed participants only of the upcoming task, but not sensory modality (Experiment 1) or whether the pre-trial cue was informative about both the upcoming task and sensory modality (Experiment 2). In addition, in both experiments switch costs between the senses were positively correlated when the sensory modality of the task repeated across trials and not when it switched. The collective evidence supports the independence of control processes mediating task switching and modality switching and also the hypothesis that switch costs reflect competitive interference between neural circuits.     

Are precues effective in proactively controlling taboo interference during speech production?

ABSTRACT

This research investigated whether precues engage proactive control to reduce emotional interference during speech production. A picture-word interference task required participants to name target pictures accompanied by taboo, negative, or neutral distractors. Proactive control was manipulated by presenting precues that signalled the type of distractor that would appear on the next trial. Experiment 1 included one block of trials with precues and one without, whereas Experiment 2 mixed precued and uncued trials. Consistent with previous research, picture naming was slowed in both experiments when distractors were taboo or negative compared to neutral, with the greatest slowing effect when distractors were taboo. Evidence that precues engaged proactive control to reduce interference from taboo (but not negative) distractors was found in Experiment 1. In contrast, mixing precued trials in Experiment 2 resulted in no taboo cueing benefit. These results suggest that item-level proactive control can be engaged under certain conditions to reduce taboo interference during speech production, findings that help to refine a role for cognitive control of distraction during speech production.     

Social intuition as a form of implicit learning: Sequences of body movements are learned less explicitly than letter sequences

In the current paper, we first evaluate the suitability of traditional serial reaction time (SRT) and artificial grammar learning (AGL) experiments for measuring implicit learning of social signals. We then report the results of a novel sequence learning task which combines aspects of the SRT and AGL paradigms to meet our suggested criteria for how implicit learning experiments can be adapted to increase their relevance to situations of social intuition. The sequences followed standard finite-state grammars. Sequence learning and consciousness of acquired knowledge were compared between 2 groups of 24 participants viewing either sequences of individually presented letters or sequences of body-posture pictures, which were described as series of yoga movements. Participants in both conditions showed above-chance classification accuracy, indicating that sequence learning had occurred in both stimulus conditions. This shows that sequence learning can still be found when learning procedures reflect the characteristics of social intuition. Rule awareness was measured using trial-by-trial evaluation of decision strategy (Dienes & Scott, 2005; Scott & Dienes, 2008). For letters, sequence classification was best on trials where participants reported responding on the basis of explicit rules or memory, indicating some explicit learning in this condition. For body-posture, classification was not above chance on these types of trial, but instead showed a trend to be best on those trials where participants reported that their responses were based on intuition, familiarity, or random choice, suggesting that learning was more implicit. Results therefore indicate that the use of traditional stimuli in research on sequence learning might underestimate the extent to which learning is implicit in domains such as social learning, contributing to ongoing debate about levels of conscious awareness in implicit learning.     

Effects of aging on implicit sequence learning: Accounting for sequence structure and explicit knowledge

The present research was intended to examine the sequence learning ability of elderly people — with a focus on comparing sequences with different structural characteristics and on properly assessing explicit knowledge. Experiment 1 showed that learning-related improvements in serial reaction time task performance were greater for young than elderly subjects, and elderly subjects were especially poor at learning a sequence with complex structural characteristics. Measures of recognition memory showed that neither young nor elderly subjects showed above-chance explicit knowledge of the sequences. Experiment 2 was designed to test the validity and sensitivity of the explicit recognition measures by comparing young subjects in groups given all random trials, given sequence trials with implicit instructions, or given sequence trials with explicit instructions. Experiment 2 confirmed the sensitivity of the recognition measures to explicit knowledge, so it is concluded that group effects in Exp. 1 reflect age-related differences in implicit learning.