Response inhibition under task switching: its strength depends on the amount of task-irrelevant response activation

Under task switch conditions, response repetitions usually produce benefits if the task also repeats, but costs if the task switches. So far, it is largely undecided how to account for these effects. In the present study, we provide additional evidence in favor of the account that each response is inhibited in order to prevent its accidental re-execution. To test this hypothesis, the risk of an accidental re-execution of a given response was manipulated by modulating the activation of the response in the previous task. In Experiment 1, this was done by means of congruent and incongruent stimuli. As expected, on task switch trials, the repetition costs were larger if a congruent rather than an incongruent stimulus occurred in the previous task. In Experiment 2, the same effect occurred for stimulus-response compatible versus incompatible stimuli in the previous task. In Experiment 3, both manipulations were applied together, which produced almost additive effects. Altogether, the results support the inhibition account for the response repetition effects under task switch conditions.     

Persisting activation in voluntary task switching: It all depends on the instructions

We tested the hypothesis that persisting activation from a previous task execution does not contribute to the switch cost in voluntary task switching. We reasoned that voluntary task switching requires the selection of random task sequences, which necessitates the active inhibition of previously executed tasks. The asymmetric switch cost was used as a marker for persisting activation. Participants switched voluntarily between color naming and word naming. One group was instructed to select unpredictable task sequences. The other group was not instructed to do so. When participants were instructed to be unpredictable, no asymmetric switch cost was observed. When participants were not instructed to be unpredictable, an asymmetric switch cost was observed. We conclude that the amount of persisting activation in voluntary task switching is limited and that the switch cost in voluntary task switching reflects the time needed for reconfiguring the cognitive system from one task to another rather than the time needed to compensate for persisting activation.     

Current task activation predicts general effects of advance preparation in task switching

Two experiments investigated the way that beforehand preparation influences general task execution in reaction-time matching tasks. Response times (RTs) and error rates were measured for switching and nonswitching conditions in a color- and shape-matching task. The task blocks could repeat (task repetition) or alternate (task switch), and the preparation interval (PI) was manipulated within-subjects (Experiment 1) and between-subjects (Experiment 2). The study illustrated a comparable general task performance after a long PI for both experiments, within and between PI madipulations. After a short PI, however, the general task performance increased significantly for the between-subjects manipulation of the PI. Furthermore, both experiments demonstrated an analogous preparation effect for both task switching and task repetitions. Next, a consistent switch cost throughout the whole run of trials and a within-run slowing effect were observed in both experiments. Altogether, the present study implies that the effects of the advance preparation go beyond the first trials and confirms different points of the activation approach (Altmann, 2002) to task switching.     

Conflict adaptation depends on task structure

The dependence of the Simon effect on the correspondence of the previous trial can be explained by the conflict-monitoring theory, which holds that a control system adjusts automatic activation from irrelevant stimulus information (conflict adaptation) on the basis of the congruency of the previous trial. The authors report on 4 experiments showing that conflict adaptation is mediated by task structure as well as previous congruency. Experiment 1 showed that for 2 completely segregated sets of stimulus-response pairs there was no conflict adaptation across sets. However, if the stimulus sets overlapped for 2 separate response sets, conflict adaptation could be observed across the response sets. Experiment 2 showed that this effect was not due to the use of stimulus-response sets lateralized to 1 hemisphere each. Experiment 3 showed that if response sets are common for 2 separate stimulus sets, then conflict adaptation can again be observed across sets. Finally, Experiment 4 showed local control effects in the absence of confounding feature-overlap effects. These results indicate that deployment of control as evidenced by conflict adaptation reflects task structure.     

Alternate response preparation in a visuomotor serial task

The preparation of a particular motor pattern is related to the information available that enables the actor to predict the correct response to a forthcoming stimulus. In many situations, however, prediction is not possible. In such cases, the individual can guess the probable parameters of the next stimulus. The authors attempted to establish the bias in the motor intention for movement and its interaction with a possible memory trace of the stimulus-response mapping produced by the preceding stimulus. Two letters were presented bilaterally, and participants (N=21) had to discriminate the target letter and respond with the compatible hand. The present findings support the existence of a memory trace of the previous stimulus-response mapping.     

Anticipating by pigeons depends on local statistical information in a serial response time task

Pigeons responded in a serial response time task patterned after that of M. J. Nissen and P. Bullemer (1987) with humans. Experiment 1 produced global facilitation: Response times in repeating lists of locations were faster than when locations were random. Response time to a spatial location was also a function of both that location's 1st- and 2nd-order local predictability, in rough agreement with the Hick-Hyman law, according to which response time is a linear function of amount of information. Experiment 2 showed that both local and global facilitation is limited to moderate response-to-stimulus intervals of about 0.50 to 2.00 s. Experiment 3 showed that response time did not depend on global statistical information. Overall, local and global performances depended on local statistical information, but global performance did not depend on global information. Local facilitation was interpreted in plain English as anticipating.     

Categorical perception depends on the discrimination task

Speech sounds are said to be perceived categorically. This notion is usually operationalized as the extent to which discrimination of stimuli is predictable from phoneme classification of the same stimuli. In this article, vowel continua were presented to listeners in a four-interval discrimination task (2IFC with flankers, or 4I2AFC) and a classification task. The results showed that there was no indication of categorical perception at all, since observed discrimination was found not to be predictable from the classification data. Variation in design, such as different step sizes or longer interstimulus intervals, did not affect this outcome, but a 2IFC experiment (without flankers, or 2I2AFC) involving the same stimuli elicited the traditional categorical results. These results indicate that the four-interval task made it difficult for listeners to use phonetic information and, hence, that categorical perception may be a function of the type of task used for discrimination.     

On spatial response code activation in a Simon task

The Simon effect refers to the performance advantage for trials where the task-irrelevant location of a target spatially corresponds with the location of the response. It is thought that the irrelevant spatial code of the target facilitates responding by automatically pre-activating the spatially corresponding response code. This spatial code is thought to passively decay shortly after its activation. In this investigation, the response was selected according to the identity of a central cue. The selected response was executed or withheld depending the identity (Experiment 1) or the presence (Experiment 2) of the target. Varying the stimulus-onset asynchrony (SOA), between the central response cue and the peripheral target, allowed for a time-course analysis of the Simon effect. The results of two experiments provided no indication that the activation level of the irrelevant spatial code decayed while the relevant response was prepared. Although reaction times increased as the SOA decreased, the Simon effect was additive with SOA, suggesting that the automatic activation of the task-irrelevant spatial code was delayed until the task-relevant response code was mostly prepared, perhaps due to the capacity limitations of response selection.     

Evidence of preliminary response preparation from a divided attention task

In a divided attention situation, preliminary response activations produced by stimuli on one channel were revealed through their effects on responses to stimuli on a secondary probe channel. Subjects performed concurrent but independent four-choice reaction-time tasks using the same four response fingers (middle and index fingers on both hands). In the main task, targets were large and small Ss and Ts, and medium-sized Ss and Ts sometimes appeared as distractors. Targets in the probe task were squares differing in location. A response to a probe square was faster if a distractor letter presented just before it had the same name as the target letter corresponding to that square (i.e., assigned to the same response key) than if the distractor letter had a different name--a result indicating that distractor letters cause partial response preparation. The timecourse of the effect demonstrated that preparation was based on preliminary information about distractor name that was available before distractor size had been determined. The results support models in which response preparation can sometimes begin before stimulus recognition has finished.     

Online response preparation in a rapid serial visual search task

Online response preparation was assessed in a visual search task using rapid serial visual presentation. In each trial, a series of letters was presented sequentially, and participants were instructed to make a target-present response if a prespecified target letter was presented or a target-absent response if it was not. Measurements of response preparation using both probe reaction time and the lateralized readiness potential indicated that preparation of the target-absent response increased near the end of the sequence. Most of the increase appeared to be due to direct priming of the target-absent response by nontarget letters, but part was due to the increased conditional probability of this response near the end of the sequence. These results extend previous studies of response preparation by showing online response preparation during a temporally extended reaction time task.     

Mental rubbernecking to negative information depends on task context

We previously demonstratedmental rubbernecking during the simple cognitive act ofrefreshing a just activated representation. Participants saw two neutral and one negative word presented simultaneously and, 425 msec later, were cued to mentally refresh (i.e., think of) one of the no-longer-present words. They were slower to refresh a neutral word than the negative word (Johnson et al., 2005, Experiment 6A). The present experiments extended that work by showing mental rubbernecking when negative items were sometimes the target of refreshing, but not when negative items were present but never the target of refreshing, indicating that expectations influence mental rubbernecking. How expectations might modulate the impact of emotional distraction is discussed.     

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.     

Holistic processing in the composite task depends on face size

Holistic processing is a hallmark of face processing. There is evidence that holistic processing is strongest for faces at identification distance 2–10 metres from the observer. However, this evidence is based on tasks that have been little used in the literature and that are indirect measures of holistic processing. We use the composite task—a well validated and frequently used paradigm—to measure the effect of viewing distance on holistic processing. In line with previous work, we find a congruency x alignment effect that is strongest for faces that are close (2 m equivalent distance) than for faces that are further away (24 m equivalent distance). In contrast, the alignment effect for same trials, used by several authors to measure holistic processing, produced results that are difficult to interpret. We conclude that our results converge with previous findings providing more direct evidence for an effect of size on holistic processing.     

Evidence for gating of direct response activation in the Simon task

TheSimon effect denotes faster responses when the task-irrelevant stimulus position corresponds to the response position than when it does not. Accounts of this effect assume that stimulus position automatically activates a spatially corresponding response while the correct response is being computed. Yet the Simon effect has been found to be reduced after noncorresponding trials. Some authors have interpreted these sequential modulations of the Simon effect as evidence for a mechanism gating positionbased response activation. Alternatively, sequential modulations have been explained in terms of feature-integration processes, which depend upon the fact that different sequences of spatial-correspondence conditions covary with different degrees of feature overlap between subsequent trials. The present study investigates whether sequential modulations of the Simon effect can occur when feature overlap in the different conditions is the same. Therefore, a Simon task with four stimulus positions and two response positions was used. Sequential modulations of the Simon effect were found in trial sequences with constant amounts of feature overlap between trials. Although the feature-integration account cannot explain this result, it is consistent with the idea of a gating (i.e., cognitive control) mechanism.     

Unconscious semantic activation depends on feature-specific attention allocation

We examined whether semantic activation by subliminally presented stimuli is dependent upon the extent to which participants assign attention to specific semantic stimulus features and stimulus dimensions. Participants pronounced visible target words that were preceded by briefly presented, masked prime words. Both affective and non-affective semantic congruence of the prime-target pairs were manipulated under conditions that either promoted selective attention for affective stimulus information or selective attention for non-affective semantic stimulus information. In line with our predictions, results showed that affective congruence had a clear impact on word pronunciation latencies only if participants were encouraged to assign attention to the affective stimulus dimension. In contrast, non-affective semantic relatedness of the prime-target pairs produced no priming at all. Our findings are consistent with the hypothesis that unconscious activation of (affective) semantic information is modulated by feature-specific attention allocation.     

Masked priming of number judgments depends on prime validity and task

The influence of brief masked primes (42 or 50 msec) on number target judgments is shown to be highly sensitive to the list-wide validity of the primes for performing a particular target task. Odd/even judgments were facilitated on parity-valid trials (e.g., 1-7) relative to parity-invalid trials (e.g., 6-7), especially when .8 rather than .2 of the trials were parity valid. The opposite pattern was observed with magnitude judgments relative to 5: Responses were facilitated on magnitude- valid trials (e.g., 6-7) relative to magnitude-invalid trials (e.g., 1-7), especially when .8 of the trials were magnitude valid. These results are consistent with Bodner and Masson's (2001) claim that a processing episode constructed during a masked prime event is more likely to be recruited when there is a high probability that it will facilitate responding to the target.     

The effect of feedback sign on task performance depends on self-concept discrepancies

Control theories claim that information about performance is often used by multiple goal systems. A proposition tested here was that performance information can create discrepancies in self-concept goals, directing cognitive resources away from the task goal system. To manipulate performance information, 160 undergraduates were given false positive or false negative normative feedback while working on a task that did or did not require substantial cognitive resources. Half of the participants were then given an opportunity to reaffirm their self-concepts following feedback, whereas half were not. Feedback sign positively related to performance only for those working on the cognitively intense task and not given a chance to reaffirm. Otherwise, feedback sign was negatively related to performance, albeit weakly.     

Children's performance on a false-belief task is impaired by activation of an evolutionarily-canalized response system

We examine whether children's performance on a false-belief task is impaired by task content that activates an early-developing, prepotent motivational system: predator-avoidance. In two studies (N = 46 and N = 37), children aged 3-4 years completed variants of a false-belief task that involved predator-avoidance, playmate-avoidance, prey-seeking, and playmate-seeking, respectively. The proportion of correct answers on the playmate-avoidance task (Study 1: 52%; Study 2: 51%) was significantly greater than the proportion of correct answers on the analogous predator-avoidance task (Study 1: 28%; Study 2: 22%). This difference was not an artifact of children generally performing better on playmate stories than on predator-prey stories. The findings are consistent with the hypothesis that activation of the predator-avoidance system generates prepotent response patterns that pre-empt full consideration of the mental states of the prey characters in false-belief stories.