Response selection and response execution in task switching: evidence from a go-signal paradigm

The present study used a go/no-go signal delay (GSD) to explore the role of response-related processes in task switching. A go/no-go signal was presented at either 100 ms or 1,500 ms after the stimulus. Participants were encouraged to use the GSD for response selection and preparation. The data indicate that the opportunity to select and prepare a response (i.e., long GSD) resulted in a substantial reduction of task-shift costs (Experiment 1) and n-2 task-repetition costs (i.e., backward inhibition; Experiment 2) in the current trial. These results suggest that interference from the preceding trial can be resolved during response selection and preparation. Furthermore, the shift costs and the n-2 repetition costs after no-go trials with long GSD (i.e., response selection but no execution) were markedly smaller than after go trials. These findings suggest that the interference that gives rise to shift costs and n-2 repetition costs is related not solely to response selection but also to response execution. Thus, the present study demonstrates dissociable contributions of response selection and response execution to interference effects in task switching.     

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.     

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.     

Effects of response selection on the task repetition benefit in task switching

A task switch typically leads to worse performance than a repetition does. This shift cost can be reduced with sufficient task preparation time, but a residual cost usually remains. We propose that a large part of this residual cost is caused by an activation bias produced by response selection processes in the preceding trial. In our experiments, we manipulated response selection requirements using a go/no-go methodology. The residual shift cost disappeared after no-go trials, suggesting that response selection is crucial to establish an activation bias for the current category-response rules and that this bias persists into the next trial. A comparison with a go-only group confirmed this analysis by revealing no differences in preparatory strategy due to the inclusion of no-go trials. In addition, no-go trials had no significant effects on subsequent trials in a single-task experiment, suggesting that no-go trials are not coded as a task different from go trials and that there is no inhibition of the prepared task in a no-go trial. We thus conclude that a persisting activation bias of response rules plays a major role in task switching.     

Response retrieval in a go/no-go priming-of-popout task

Priming of popout is the finding that singleton search is faster when features of a target and of nontargets are repeated across trials than when the features switch. Theoretical accounts suggest that intertrial repetition influences perceptual and attentional selection processes, episodic retrieval processes, or both. The present study combined a popout search task with a go/no-go task. In Experiment 1, the nontarget distractors in each display carried the go/no-go feature, and in Experiment 2, the texture of all items carried the go/no-go feature. Results showed that the go/no-go task moderated the intertrial repetition effects. In Experiment 1, the target color elicited retrieval of the preceding distractor color and associated no-go response, resulting in larger interference effects. In Experiment 2, the target color elicited retrieval of the preceding target color and no-go response, resulting in reduced facilitation effects. Additional results from both experiments showed that the colors in a search display also influenced target selection on the following trial. Taken together, the results of both experiments suggest that intertrial repetition influences both early selection and postselection retrieval processes.     

Backward crosstalk effects in psychological refractory period paradigms: effects of second-task response types on first-task response latencies

Three experiments using psychological refractory period (PRP) tasks documented backward crosstalk effects in which the nature of the second-task response influenced the first-task response latencies. Such effects are difficult to explain within currently popular bottleneck models, according to which second-task response selection does not begin until first-task response selection has finished. In Experiments 1 and 2, the first of the PRP tasks required a choice reaction time (RT) response, whereas the second task required a go/no-go decision. Task 1 responses were faster when the second task required a go response than when it required a no-go response. Experiment 3 showed that Task 1 RTs were also influenced by the complexity of second-task responses. These backward crosstalk effects indicate that significant second-task processing is carried out in time to influence first-task responses and thus challenge strictly serial bottleneck models.     

Attention and gaze shifting in dual-task and go/no-go performance with vocal responding

Evidence from go/no-go performance on the Eriksen flanker task with manual responding suggests that individuals gaze at stimuli just as long as needed to identify them (e.g., Sanders, 1998). In contrast, evidence from dual-task performance with vocal responding suggests that gaze shifts occur after response selection (e.g., Roelofs, 2008a). This difference in results may be due to the nature of the task situation (go/no-go vs. dual task) or the response modality (manual vs. vocal). We examined this by having participants vocally respond to congruent and incongruent flanker stimuli and shift gaze to left- or right-pointing arrows. The arrows required a manual response (dual task) or determined whether the vocal response to the flanker stimuli had to be given or not (go/no-go). Vocal response and gaze shift latencies were longer on incongruent than congruent trials in both dual-task and go/no-go performance. The flanker effect was also present in the manual response latencies in dual-task performance. Ex-Gaussian analyses revealed that the flanker effect on the gaze shifts consisted of a shift of the entire latency distribution. These results suggest that gaze shifts occur after response selection in both dual-task and go/no-go performance with vocal responding.     

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.     

Under what conditions do young children have difficulty inhibiting manual actions?

Understanding how responses become prepotent is essential for understanding when inhibitory control is needed in everyday behavior. The authors investigated the conditions under which manual actions became prepotent in a go/no-go task. Children had to open boxes that contained stickers on go trials and leave shut boxes that were empty on no-go trials. In Experiment 1 (n = 40, mean age = 3.6 years), the authors obtained evidence consistent with this task requiring inhibitory control. Results of Experiment 2 (n = 40, mean age = 3.7 years) suggested that box opening was prepotent because (a) opening is the habitual action associated with boxes and (b) children planned to open boxes on go trials of the task. Experiment 3 (n = 96, mean age = 3.5 years) showed that even empty boxes elicited the same errors and that delaying responding reduced errors even though the delay occurred before the cue that indicated the correct response (contrary to a rule reflection account). Because the delay occurred after box presentation, performance was consistent with a transient activation account. Delay training might benefit children with weak inhibition.     

An electrophysiological study of the insertion of overt response choice

Using electrophysiological measures, the authors studied changes in prestimulus state, stimulus identification, and response-related processing when, in a go/no-go task, forced choice between 2 overt go responses was inserted. The authors observed decreased prestimulus motor preparation (electromyogram), no change in stimulus identification time (selection negativity), a minor increase in response selection time (lateralized readiness potential), a large increase in response preparation time (lateralized readiness potential), a minor effect on response execution time (electromyogram), and a decrease in the activation of a response-inhibition process on no-go trials (frontal event-related potential). The existence of the response-inhibition process was verified by the presence of inverted lateralized readiness potentials on no-go trials. Pure insertion of response choice in a task seems impossible because the choice between activation and inhibition (go/no-go) always seems already present.     

The go/no-go priming task: automatic evaluation and categorisation beyond response interference

The response-window version of a go/no-go (GNG) response priming task is introduced using both evaluative (Experiment 1) and animacy decision (Experiment 2). In each trial a cue indicates which target category should lead to a key-press. The target is preceded by either a congruent or incongruent prime. The standard priming task was added as well. Both tasks yielded robust priming effects. However, they differed regarding a signature of response activation paradigms, that is, the Gratton effect (i.e. smaller priming effects following incongruent trials compared to congruent trials), which is present in the standard task but absent in the GNG task. This indicates that effects found with the GNG task are caused by different processes compared to the standard task. Experiment 3 tested an alternative account to explain priming effects in the GNG task. By manipulating response biases, Experiment 3 provides evidence for this account.     

The role of response inhibition in temporal preparation: Evidence from a go/no-go task

During the foreperiod (FP) of a warned reaction task, participants engage in a process of temporal preparation to speed response to the impending target stimulus. Previous neurophysiological studies have shown that inhibition is applied during FP to prevent premature response. Previous behavioral studies have shown that the duration of FP on both the current and the preceding trial codetermine response time to the target. Integrating these findings, the present study tested the hypothesis that the behavioral effects find their origin in response inhibition on the preceding trial. In two experiments the variable-FP paradigm was combined with a go/no-go task, in which no-go stimuli required explicit response inhibition. The resulting data pattern revealed sequential effects of both FP (long or short) and response requirement (go or no-go), which could be jointly understood as expressions of response inhibition, consistent with the hypothesis.     

A response-discrimination account of the Simon effect

Simon effects might partly reflect stimulus-triggered response activation. According to the response-discrimination hypothesis, however, stimulus-triggered response activation shows up in Simon effects only when stimulus locations match the top-down selected spatial codes used to discriminate between alternative responses. Five experiments support this hypothesis. In Experiment 1, spatial codes of each response differed by horizontal and vertical axis position, yet one axis discriminated between alternative responses, whereas the other did not. Simon effects resulted for targets on discriminating axes only. In Experiment 2, both spatial axes discriminated between responses, and targets on both axes produced Simon effects. In Experiment 3, Simon effects resulted for a spatial choice-reaction task but not for a go/no-go task. Even in the go/no-go task, a Simon effect was restored when a two-choice reaction task preceded the go/no-go task (Experiment 4) or when participants initiated trials with responses spatially discriminated from the go response (Experiment 5).     

The N2 in go/no-go tasks reflects conflict monitoring not response inhibition

The functional significance of the N2 in go/no-go tasks was investigated by comparing electrophysiological data obtained from two tasks: a go/no-go task involving both response inhibition as well as response conflict monitoring, and a go/GO task associated with conflict monitoring only. No response was required to no-go stimuli, and a response with maximal force to GO stimuli. The relative frequency of the go stimuli (80% vs. 50%) was varied. The N2 peaked on both no-go and GO trials, with larger amplitudes for both signals when presented in a context of frequent (80%) go signals. These results support the idea that the N2 reflects conflict monitoring not response inhibition.     

Electrophysiological correlates of anterior cingulate function in a go/no-go task: Effects of response conflict and trial type frequency

Neuroimaging and computational modeling studies have led to the suggestion that response conflict monitoring by the anterior cingulate cortex plays a key role in cognitive control. For example, response conflict is high when a response must be withheld (no-go) in contexts in which there is a prepotent tendency to make an overt (go) response. An event-related brain potential (ERP) component, the N2, is more pronounced on no-go than on go trials and was previously thought to reflect the need to inhibit the go response. However, the N2 may instead reflect the high degree of response conflict on no-go trials. If so, an N2 should also be apparent when subjects make a go response in conditions in which nogo events are more common. To test this hypothesis, we collected high-density ERP data from subjects performing a go/no-go task, in which the relative frequency of go versus no-go stimuli was varied. Consistent with our hypothesis, an N2 was apparent on both go and no-go trials and showed the properties expected of an ERP measure of conflict detection on correct trials: (1) It was enhanced for low-frequency stimuli, irrespective of whether these stimuli were associated with generating or suppressing a response, and (2) it was localized to the anterior cingulate cortex. This suggests that previous conceptions of the no-go N2 as indexing response inhibition may be in need of revision. Instead, the results are consistent with the view that the N2 in go/no-go tasks reflects conflict arising from competition between the execution and the inhibition of a single response.     

Conditions under which children experience inhibitory difficulty with a "button-press" go/no-go task

Go/no-go tasks seem to provide a simple marker of inhibitory development in young children. Children are told to respond to one stimulus on go trials but to make no response to another stimulus on no-go trials; responding on no-go trials is assumed to reflect a failure to inhibit the go response. However, there is evidence to suggest that a type of go/no-go task, which we call the "button-press" task, does not require inhibition. We investigated the conditions under which young children (M=3 years 6 months, N=120) experience inhibitory difficulty with this type of task. The data suggest that the speed of stimulus presentation is crucial and that other studies using this type of task have presented the stimuli too briefly. The importance of establishing the inhibitory credentials of a task before it is used as a marker of inhibitory control is emphasized.     

The role of the prefrontal cortex in the go/no-go task in humans: a positron emission tomography study

To study the localization of response inhibition in the human brain, especially the role of the prefrontal cortex and laterality of its activation, we used positron emission tomography (PET) to measure regional cerebral blood flow in 11 right-handed participants while they performed a go/no-go and a simple control reaction-time task. In the control task, the participants responded to a target stimulus following a cue stimulus. In the go/no-go task they were instructed to inhibit the required response if the target stimulus did not appear. These tasks were performed using each hand. The right prefrontal cortex was found to be significantly activated when the go/no-go task was compared with the control task, regardless of the responding hand. The results indicated that response inhibition per se may be controlled by the right prefrontal cortex regardless of response hand for right-handed participants.     

Changing internal constraints on action: the role of backward inhibition

Flexible control of action requires the ability to disengage from previous goals or task sets. The authors tested the hypothesis that disengagement during intentional shifts between task sets is accompanied by inhibition of the previous task set ("backward inhibition"). As an expression of backward inhibition the authors predicted increased response times when shifting to a task set that had to be abandoned recently and, thus, suffers residual inhibition. The critical backward inhibition effect on the level of abstractly defined perceptual task sets was obtained across 6 different experiments. In addition, it was shown that backward inhibition can be differentiated from negative priming (Experiment 2), that it is tied to top-down sequential control (Experiment 3), that it can account at least partially for "residual shift costs" in set-shifting experiments (Experiment 4), and that it occurs even in the context of preplanned sequences of task sets (Experiment 5).     

Temporal preparation,response inhibition and impulsivity

Temporal preparation and impulsivity involve overlapping neural structures (prefrontal cortex) and cognitive functions (response inhibition and time perception), however, their interrelations had not been investigated. We studied such interrelations by comparing the performance of groups with low vs. high non-clinical trait impulsivity during a temporal preparation go no-go task. This task measured, in less than 10 min, how response inhibition was influenced both by temporal orienting of attention (guided by predictive temporal cues) and by sequential effects (produced by repetition/alternation of the duration of preparatory intervals in consecutive trials). The results showed that sequential effects produced dissociable patterns of temporal preparation as a function of impulsivity. Sequential effects facilitated both response speed (reaction times – RTs – to the go condition) and response inhibition (false alarms to the no-go condition) selectively in the low impulsivity group. In the high impulsivity group, in contrast, sequential effects only improved RTs but not response inhibition. We concluded that both excitatory and inhibitory processing may be enhanced concurrently by sequential effects, which enables the temporal preparation of fast and controlled responses. Impulsivity could hence be related to less efficient temporal preparation of that inhibitory processing.     

Inhibition of response mode in task switching

Task inhibition was explored in two experiments that employed a paradigm in which participants switched among three tasks. Two tasks required manual choice responses based on numerical judgment (parity or magnitude), whereas a third task required an unconditional double-press of both response keys. Both experiments showed that switching to a just-abandoned task (n-2 task repetition) generally leads to a performance cost relative to switching to another task. Specifically, this task inhibition effect also occurred for the double-press task, suggesting inhibition of response mode. Prolonging the task-cuing interval showed that advance task preparation reduced only inhibition of the double-press task but not of the choice tasks (Experiment 1). Prolonging the response-cue interval led to a decrease of the inhibition effect in all tasks (Experiment 2), suggesting a time-based release of task inhibition. Together, the experiments support the notion of a response-related component of task inhibition.