Inhibiting prepared and ongoing responses: Is there more than one kind of stopping?

Inhibiting movements has been investigated widely using the countermanding (stop signal) paradigm. Although it has been assumed that response inhibition, as measured by the countermanding task, generalizes to all forms of stopping, this has never been tested. In the present study, stopping performance in the countermanding paradigm was compared with stopping performance in a new paradigm in which a continuous-tracking task was used. Although stimulus presentations were matched across paradigms, the two tasks differed in the type of stopping required. In the countermanding paradigm, response inhibition latency was measured prior to response execution-this is, it was inferred from the successful withholding of a go response. In the new paradigm, response inhibition was carried out after response execution-that is, it was measured as the time to begin stopping a continuous tracking response. Results indicated that stopping latencies between the two paradigms were highly correlated, providing strong evidence that stopping an unexecuted response engages the same mechanisms as stopping an ongoing response.     

Inhibitory effects on response force in the stop-signal paradigm

The forcefulness of key press responses was measured in stop-all and selective stopping versions of the stop-signal paradigm. When stop signals were presented too late for participants to succeed in stopping their responses, response force was nonetheless reduced relative to trials in which no stop signal was presented. This effect shows that peripheral motor aspects of primary task responses can still be influenced by inhibition even when the stop signal arrives too late to prevent the response. It thus requires modification of race models in which responses in the presence of stop signals are either stopped completely or produced normally, depending on whether the responding or stopping process finishes first.     

On the difference between response inhibition and negative priming: Evidence from simple and selective stopping

Negative priming is a commonly observed after-effect in studies concerning inhibition. Effects of the preceding trial are also found in other paradigms, like the stop signal paradigm. In the present study, stop signals were introduced in a negative priming paradigm and the relation between stop signal inhibition and negative priming was investigated. In Experiment 1, we used a simple stop signal task. Stopping data clearly suggest that stopping performance was not influenced by negative priming. Interestingly, on no-signal probes the negative priming effect disappeared after successful inhibition of the response on the prime trial. On the contrary, when inhibition failed, the negative priming effect remained. In Experiment 2, we used the selective stop signal task. As in Experiment 1, inhibition of motor responses was not influenced by negative priming. The hypothesis that negative priming disappeared due to a general nonspecific stop was confirmed in this experiment, as a negative priming effect was found after both successful and unsuccessful behavioral inhibition. The results of both experiments show that response inhibition is not influenced by negative priming, and that negative priming is only affected after a successful general stop.     

Reduced response readiness delays stop signal inhibition

This study examines the effect of response readiness on the stopping of motor responses. Thirteen subjects performed a primary task requiring a speeded choice reaction on go trials and response inhibition on nogo trials. An occasional cue informed subjects that a nogo trial was imminent but left them uncertain about the number of go trials separating the cue and the upcoming nogo trial. This setup was meant to create test episodes of reduced response readiness (i.e., trial sequences initiated by the cue and terminated by the nogo signal) and control episodes, in which subjects were ready to execute a speeded choice reaction (i.e., trial sequences consisting only of go trials). During both episodes, a visual stop signal could occasionally and unpredictably follow go signal onset, instructing subjects to withhold their response to the go signal. Choice reactions on go trials were delayed during test episodes relative to control episodes. Most importantly, stop reactions were delayed, not facilitated, during test episodes compared to control episodes. These findings were taken to suggest that reduced readiness gives rise to more forceful responses that are then more difficult to inhibit.     

Post-stop-signal adjustments: inhibition improves subsequent inhibition

Performance in the stop-signal paradigm involves a balance between going and stopping, and one way that this balance is struck is through shifting priority away from the go task, slowing responses after a stop signal, and improving the probability of inhibition. In 6 experiments, the authors tested whether there is a corresponding shift in priority toward the stop task, speeding reaction time to the stop signal. Consistent with this hypothesis, stop-signal reaction time (SSRT) decreased on the trial immediately following a stop signal in each experiment. Experiments 2-4 used 2 very different stop signals within a modality, and stopping improved when the stop stimulus repeated and alternated. Experiments 5 and 6 presented stop signals in different modalities and showed that SSRT improved only when the stop stimulus repeated within a modality. These results demonstrate within-modality post-stop-signal speeding of response inhibition.     

The duration of response inhibition in the stop-signal paradigm varies with response force

In a previous study, we have found that the speed of stopping a response is delayed when response readiness is reduced by cuing the probability of no-go trials [Acta Psychol. 111 (2002) 155]. Other investigators observed that responses are more forceful when the probability to respond is low than when it is high (e.g. [Quart. J. Exp. Psychol. A 50 (1997) 405]). In this study, the hypothesis was tested that low probability responses are more forceful than high probability responses and that these responses are more difficult to stop. Subjects performed on a choice reaction task and on three tasks with respectively 100%, 80%, and 50% response probabilities. Stop signals were presented on 30% of the trials, instructing subjects to withhold their response. Response force on non-signal (go) trials and the duration of response inhibition on signal (stop) trials increased as response probability decreased. This pattern of findings was interpreted to support the hypothesis predicting that stopping is more difficult when response readiness is low than when it is high.     

A Bayesian approach for estimating the probability of trigger failures in the stop-signal paradigm

Response inhibition is frequently investigated using the stop-signal paradigm, where participants perform a two-choice response time task that is occasionally interrupted by a stop signal instructing them to withhold their response. Stop-signal performance is formalized as a race between a go and a stop process. If the go process wins, the response is executed; if the stop process wins, the response is inhibited. Successful inhibition requires fast stop responses and a high probability of triggering the stop process. Existing methods allow for the estimation of the latency of the stop response, but are unable to identify deficiencies in triggering the stop process. We introduce a Bayesian model that addresses this limitation and enables researchers to simultaneously estimate the probability of trigger failures and the entire distribution of stopping latencies. We demonstrate that trigger failures are clearly present in two previous studies, and that ignoring them distorts estimates of stopping latencies. The parameter estimation routine is implemented in the BEESTS software (Matzke et al., Front. Quantitative Psych. Measurement, 4, 918; 2013a) and is available at http://dora.erbe-matzke.com/software.html.     

The development of selective inhibitory control: The influence of verbal labeling

The role of language in the development of selective inhibitory control was examined in four groups: Children aged 7-9 years, children aged 11-13 years, adults aged 20-27 years, and adults aged 62-76 years. We used a modified stop-signal task in which participants inhibited or executed responses based on a visual signal. Response execution and inhibition were assessed by measurement of reaction times (RTs) and error rates to a go signal and RTs to a stop signal. Four task variations were compared in which subjects named (1) the stimulus, (2) the intended action (go/stop), (3) something irrelevant, or (4) nothing. Results showed different developmental trends for response execution and inhibition across the lifespan. Moreover, response execution was faster and more accurate when subjects named the stimulus instead of the intended action. The increase in response accuracy when naming the stimulus was greatest for children. In contrast to expectations, naming the intended action did not influence response inhibition. Overall, these findings suggest that verbal labeling supports the initiation but not the inhibition of actions.     

Countermanding saccades: evidence against independent processing of go and stop signals

In a stop signal paradigm, subjects were instructed to make a saccade to a visual target appearing left or right of the fixation point. In 25% of the trials, an auditory stop signal was presented after a variable delay that required the subject to inhibit the saccade. Observed saccadic response times in stop failure trials were longer than predicted by Logan and Cowan's (1984) race model. Saccadic response time and amplitude decreased with the time between stop signal presentation and saccade execution, suggesting an inhibitory effect between the stop signal and the go signal processes that is not compatible with an independent race assumption. Moreover, countermanding a saccade was more difficult when stop and go signals appeared at the same location.     

Redundancy gain in the stop-signal paradigm: implications for the locus of coactivation in simple reaction time

The authors carried out 2 experiments designed to cast light on the locus of redundancy gain in simple visual reaction time by using a stop-signal paradigm. In Experiment 1, the authors found that single visual stimuli were more easily inhibited than double visual stimuli by an acoustic stop signal. This result is in keeping with the idea that redundancy gain occurs prior to the ballistic stage of the stop-signal task. In Experiment 2, the authors found that the response to an acoustic go signal was more easily inhibited by a double than by a single visual stop signal. This result provides conclusive evidence for a redundancy gain in the stop process--in a process that does not involve a motor response but rather its inhibition.     

Stopping and restarting an unfolding action at various times.

The ability to inhibit an unfolding action is usually investigated using a stop signal (or gostop) task. The data from the stop-signal task are often described using a horse-race model whose key assumption is that each process (i.e., go, stop) exhibits stochastic independence. Using three variations of a coincident-timing task (i.e., go, gostop, and gostopgo) we extend previous considerations of stochastic independence by analysing the go latencies for prior effects of stopping. On random trials in the gostopgo task the signal sweep was paused for various times at various distances before the target. Significant increases in latency errors were reported on those trials on which the signal was paused (p <.005). Further analyses of the pause trials revealed significant effects for both the stopping interval (p <.001) and the pause interval (p <.05). Tukey post hoc analyses demonstrated increased latency errors as a linear function of the stopping interval, as expected, and decreased latency errors as a nonlinear function of the pause interval. These latter results indicate that the latencies of the go process, as reflected in the latency errors, may not exhibit stochastic independence under certain conditions. Various control mechanisms were considered in an attempt to explain these data.     

A developmental study of attention to auditory and visual signals

Three experiments tested for developmental changes in attention to simple auditory and visual signals. Subject pressed a single button in response to the onset (Experiment 1) or offset (Experiment 2) of either a tone or a light. During one block of trials subjects knew which stimulus would come on or go off on each trial (precue condition) whereas during the other block of trials no precue was provided. In both experiments subjects as young as 4 years old responded more rapidly with precues, indicating that they were able to allocate their attention to the indicated modality. Experiment 3 utilized a choice reaction paradigm (in which subjects pressed different buttons in response to the onset of the light and the tone) in order to examine their attention allocation when no precues were provided. It was found that the adults and 7-year-olds tended to allocate their attention to vision rather than audition when no precue was provided. The results with the 4-year-olds were not entirely consistent, but suggested a similar biasing of attention to vision on their part as well.     

Attentional localization prior to simple and directed manual responses

The relationship between attention and the programming of motor responses was investigated, using a paradigm in which the onsets of targets for movements were preceded by peripheral attentional cues. Simple (button release) and reaching manual responses were compared under conditions in which the subjects either made saccades toward the target location or refrained from making eye movements. The timing of the movement onset was used as the dependent measure for both simple and reaching manual responses. Eye movement latencies were also measured. A follow-up experiment measured the effect of the same peripheral cuing procedure on purely visual processes, using signal detection measures of visual sensitivity and response bias. The results of the first experiment showed that reaction time (RT) increased with the distance between the cued and the target locations. Stronger distance effects were observed when goal-directed responses were required, which suggests enhanced attentional localization of target positions under these conditions. The requirement to generate an eye movement response was found to delay simple manual RTs. However, mean reaching RTs were unaffected by the eye movement condition. Distance gradients on eye movement latencies were relatively shallow, as compared with those on goal-directed manual responses. The second experiment showed that the peripheral cue had only a very small effect on visual detection sensitivity in the absence of directed motor responses. It is concluded that cue-target distance effects with peripheral cues are modulated by the motor-programming requirements of the task. The effect of the peripheral cue on eye movement latencies was qualitatively different from that observed on manual RTs, indicating the existence of separate neural representations underlying both response types. At the same time, the interactions between response modalities are consistent with a supramodal representation of attentional space, within which different motor programs may interact.     

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.     

Switching between tasks and responses: a developmental study

Task switching requires the ability to flexibly switch between task rules and responses, and is sensitive to developmental change. We tested the hypothesis that developmental changes in task switch performance are associated with changes in the facilitating or interfering effect of the previously retrieved stimulus-response (S-R) association. Three age groups (7-8-year-olds, 10-12-year-olds and 20-25-year-olds) performed a two-choice reaction time (RT) task in which spatially compatible or incompatible responses were required. The RT costs associated with switching between tasks were larger when responses were repeated than when responses were alternated. Younger children showed a greater cost than adults when switching between tasks but repeating responses. This age difference decreased when the interval between the previous response and the upcoming stimulus increased. Switch costs were larger when switching to the compatible task than to the incompatible task, but this effect did not differ between age groups. These findings suggest that young children build up stronger transient associations between task sets and response sets, which interfere with their ability to switch to currently intended actions. A similar pattern has previously been observed for older adults (Mayr, 2001), suggesting a common contributor to task switching deficits across the life span.     

Attentional localization prior to simpleand directed manual responses

The relationship between attention and the programming of motor responses was investigated, using a paradigm in which the onsets of targets for movements were preceded by peripheral attentional cues. Simple (button release) and reaching manual responses were compared under conditions in which the subjects either made saccades toward the target location or refrained from making eye movements. The timing of the movement onset was used as the dependent measure for both simple and reaching manual responses. Eye movement latencies were also measured. A follow-up experiment measured the effect of the same peripheral cuing procedure on purely visual processes, using signal detection mea-sures of visual sensitivity and response bias. The results of the first experiment showed that reaction time (RT) increased with the distance between the cued and the target locations. Stronger distance ef-fects were observed when goal-directed responses were required, which suggests enhanced attentional localization of target positions under these conditions. The requirement to generate an eye movement response was found to delay simple manual RTs. However, mean reaching RTs were unaffected by the eye movement condition. Distance gradients on eye movement latencies were relatively shallow, as compared with those on goal-directed manual responses. The second experiment showed that the peripheral cue had only a very small effect on visual detection sensitivity in the absence of directed motor responses. It is concluded that cue-target distance effects with peripheral cues are modulated by the motor-programming requirements of the task. The effect of the peripheral cue on eye movement latencies was qualitatively different from that observed on manual RTs, indicating the existence of separate neural representations underlying both response types. At the same time, the interactions be-tween response modalities are consistent with a supramodal representation of attentional space, within which different motor programs may interact.     

IMPULSIVITY AND INHIBITORY CONTROL

Abstract— We report an experiment testing the hypothesis that impulsive behavior reflects a deficit in the ability to inhibit prepotent responses Specifically, we examined whether impulsive people respond more slowly to signals to inhibit (stop signals) than non-impulsive people In this experiment, 136 undergraduate students completed an impulsivity questionnaire and then participated in a stop-signal experiment, in which they performed a choice reaction time (go) task and were asked to inhibit their responses to the go task when they heard a stop signal The delay between the go signal and the stop signal was determined by a tracking procedure designed to allow subjects to inhibit on 50% of the stop-signal trials. Reaction time to the go signal did not vary with impulsivity, but estimated stop-signal reaction time was longer in more impulsive subjects, consistent with the hypothesis and consistent with results from populations with pathological problems with impulse control.     

Restraint and Cancellation: Multiple Inhibition Deficits in Attention Deficit Hyperactivity Disorder

We used variations of the stop signal task to study two components of motor response inhibition—the ability to withhold a strong response tendency (restraint) and the ability to cancel an ongoing action (cancellation)—in children with a diagnosis of attention deficit hyperactivity disorder (ADHD) and in non-ADHD controls of similar age (ages 7–14 years). The goal was to determine if restraint and cancellation were related and if both were deficient in ADHD. The stop signal task involved a choice reaction time task (go task) which required a rapid response. The demand for inhibitory control was invoked through the presentation of a stop signal on a subset of go trials which required that the ongoing response be suspended. The stop signal was presented either concurrently with the go signal (restraint version) or after a variable delay (cancellation version). In Study 1, we compared ADHD and control children on the cancellation version of the stop task; in Study 2, we compared ADHD and controls on the restraint version. In Study 3, a subset of ADHD and control participants completed both tasks so that we could examine convergence of these dimensions of inhibition. Compared to control participants, ADHD participants showed a deficit both in the ability to cancel and to restrain a speeded motor response. Performance on the restraint version was significantly correlated with performance on the cancellation version in controls, but not in ADHD participants. We conclude that ADHD is associated with deficits in both restraint and cancellation subcomponents of inhibition.     

Balancing cognitive demands: control adjustments in the stop-signal paradigm

Cognitive control enables flexible interaction with a dynamic environment. In 2 experiments, the authors investigated control adjustments in the stop-signal paradigm, a procedure that requires balancing speed (going) and caution (stopping) in a dual-task environment. Focusing on the slowing of go reaction times after stop signals, the authors tested 5 competing hypotheses for post-stop-signal adjustments: goal priority, error detection, conflict monitoring, surprise, and memory. Reaction times increased after both successful and failed inhibition, consistent with the goal priority hypothesis and inconsistent with the error detection and conflict hypotheses. Post-stop-signal slowing was greater if the go task stimulus repeated on consecutive trials, suggesting a contribution of memory. We also found evidence for slowing based on more than the immediately preceding stop signal. Post-stop-signal slowing was greater when stop signals occurred more frequently (Experiment 1), inconsistent with the surprise hypothesis, and when inhibition failed more frequently (Experiment 2). This suggests that more global manipulations encompassing many trials affect post-stop-signal adjustments.     

The interplay of stop signal inhibition and inhibition of return

Inhibition of return (IOR) refers to slower responding to a stimulus that appears in the same rather than a different location as that of a preceding stimulus. The goal of the present study was to examine the relationship between IOR and stop signal inhibition. Participants were presented with two stimuli (S1 and S2) on each trial. On half of the trials (go trials), participants were required to make a speeded button-press response to report the location of S1; on the other half of trials (stop trials), they were required to cancel the response to S1, as indicated by the appearance of a stop signal at a variable delay (stop signal delay, SSD) after the appearance of S1. Success in cancelling an S1 response varied directly as a function of the SSD: The longer the delay, the more difficult it was for participants to cancel the prepared response. We examined the magnitude of IOR in the S2 reaction times as a function of whether participants made a correct go response to S1, made an erroneous non-cancelled response to S1, or successfully cancelled a response to S1. Our results indicated that the presentation of a stop signal increased the magnitude of IOR, even when the S1 response was not successfully cancelled. However, this was true only when the to-be-cancelled response involved the same effectors as the response used to reveal IOR. These results suggest that there may be a motor component to IOR that is sensitive to the same inhibitory processes that are used to cancel responses in a stop signal paradigm.