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.     

Response force in RT tasks: Isolating effects of stimulus probability and response probability

Mattes, UIrich, and Miller (1997) found that as response probability decreases in a simple reaction time (RT) task, participants produce more forceful responses as well as longer RTs, suggesting a direct influence of preparatory processes on the motor system. In this previous study, however, response probability was confounded with stimulus probability, leaving open the possibility that response force was sensitive to stimulus- rather than response-related preparation. The present study was conducted to unravel the effects of stimulus and response probability. Experiment 1 manipulated stimulus probability and revealed that responses to a more probable stimulus are less forceful than responses to a less probable stimulus even when both stimuli require the same response. Experiment 2 demonstrated that this stimulus probability effect does not depend on the overall level of response probability. Experiment 3 showed an analogous effect for response probability when stimulus probability is kept constant. The complete pattern of results suggests that both stimulus probability and response probability affect the forcefulness of a response. It is argued that response probability exerts adirect influence on the motor system, whereas stimulus probability influences the motor system indirectly via premotoric adjustments.     

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.     

Developmental trends in simple and selective inhibition of compatible and incompatible responses

This study examined age-related change in the ability to inhibit responses using two varieties of the stop signal paradigm. Three age groups (29 7-year-olds, 24 10-year-olds, and 28 young adults) performed first on a visual choice reaction task in which the spatial mapping between the go signal and response was varied between blocks. The choice task was then complicated by randomly inserting a visual stop signal on 30% of the trials. In the simple stop signal paradigm, the stop signal required the inhibition of the planned response. In the selective stop signal paradigm, the stop signal required response inhibition only when the stop signal was presented at the same side as the instructed response to the go signal. The results showed that simple stopping was faster than selective stopping and that selective, but not simple, stopping of incompatible responses was slower than stopping of compatible responses. Brinley plot analysis yielded linear functions relating children's latencies to adults' latencies. Analysis of shared variance indicated that developmental change in the speed of selective stopping continued to be significant even when the effect associated with simple stopping was removed. This pattern of findings is discussed vis-à-vis notions of global versus specific developmental trends in the speed of information processing.     

Effects of stimulus-stimulus compatibility and stimulus-response compatibility on response inhibition

Previous studies demonstrated that interference control in stimulus–stimulus compatibility tasks slowed down stopping in the stop signal task (e.g., Kramer, A. F., Humphrey, D. G., Larish, J. F., Logan, G. D., & Strayer, D. L. (1994). Aging and inhibition: beyond a unitary view of inhibitory processing in attention. psychology and aging, 9, 491–512). In the present study, the impact of stimulus–stimulus compatibility and stimulus–response compatibility on response inhibition is further investigated. In Experiment 1, the stop signal task was combined with a traditional horizontal Simon task and with a vertical variant. For both dimensions, stopping responses was prolonged in incompatible trials, but only when the previous trial was compatible. In Experiment 2, the Simon task was combined with a spatial Stroop task in order to compare the effects of stimulus–stimulus and stimulus–response compatibility. The results demonstrated that both types of compatibility influenced stopping in a similar way. These findings are in favor of the hypothesis that response inhibition in the stop signal task and interference control in conflict tasks rely on similar mechanisms.     

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.     

Effects of stop-signal probability in the stop-signal paradigm: the N2/P3 complex further validated

The aim of this study was to examine the effects of frequency of occurrence of stop signals in the stop-signal paradigm. Presenting stop signals less frequently resulted in faster reaction times to the go stimulus and a lower probability of inhibition. Also, go stimuli elicited larger and somewhat earlier P3 responses when stop signals occurred less frequently. Since the amplitude effect was more pronounced on trials when go signals were followed by fast than slow reactions, it probably reflected a stronger set to produce fast responses. N2 and P3 components to stop signals were observed to be larger and of longer latency when stop signals occurred less frequently. The amplitude enhancement of these N2 and P3 components were more pronounced for unsuccessful than for successful stop-signal trials. Moreover, the successfully inhibited stop trials elicited a frontocentral P3 whereas unsuccessfully inhibited stop trials elicited a more posterior P3 that resembled the classical P3b. P3 amplitude in the unsuccessfully inhibited condition also differed between waveforms synchronized with the stop signal and waveforms synchronized with response onset whereas N2 amplitude did not. Taken together these findings suggest that N2 reflected a greater significance of failed inhibitions after low probability stop signals while P3 reflected continued processing of the erroneous response after response execution.     

Response inhibition during perceptual decision making in humans and macaques

Response inhibition in stop signal tasks has been explained as the outcome of a race between GO and STOP processes (e.g., Logan, 1981). Response choice in two-alternative perceptual categorization tasks has been explained as the outcome of an accumulation of evidence for the alternative responses. To begin unifying these two powerful investigation frameworks, we obtained data from humans and macaque monkeys performing a stop signal task with responses guided by perceptual categorization and variable degrees of difficulty, ranging from low to high accuracy. Comparable results across species reinforced the validity of this animal model. Response times and errors increased with categorization difficulty. The probability of failing to inhibit responses on stop signal trials increased with stop signal delay, and the response times for failed stop signal trials were shorter than those for trials with no stop signal. Thus, the Logan race model could be applied to estimate the duration of the stopping process. We found that the duration of the STOP process did not vary across a wide range of discrimination accuracies. This is consistent with the functional, and possibly mechanistic, independence of choice and inhibition mechanisms.     

Partial response activation to masked primes is not dependent on response readiness

Masked primes presented foveally prior to a target trigger an initial partial activation of their corresponding response, followed by an inhibition of the same response. The latter phase results in performance costs on compatible trials and performance benefits on incompatible trials relative to neutral trials (negative compatibility effect). The present study investigated whether this activation-follow-by-inhibition process depends on the overall or specific state of response readiness. In two masked priming experiments, response readiness was manipulated by varying the relative frequency of Go-trials in a Go/NoGo task (Exp. 1) and the relative frequency of left- and right-hand responses in a 2-alternative choice reaction time task (Exp. 2). In both experiments, mean reaction times were longer for infrequent responses than for frequent responses. However, negative compatibility effects were not affected by response frequency. This result indicates that neither the general ability of masked primes to elicit a partial motor activation nor the specific time course of this process is dependent on response readiness. It is concluded that response readiness affects the execution of an overt response rather than the initial activation of this response.     

Voluntarily-generated unimanual preparation is associated with stopping success: evidence from LRP and lateralized mu ERD before the stop signal

According to the race models of the stop-signal paradigm, stopping success (successful vs. unsuccessful stopping) is attributed to the finishing times of a go and a stop process. In addition to those factors involving processing times, in the present study we sought to use electrophysiological measures to find factors involving activations that could affect stopping success. We hypothesized that voluntarily-generated unimanual preparation would be a factor. To assess voluntarily-generated unimanual preparation in the stop-signal paradigm, we used a selective-stopping task without any precue. The selective-stopping task also allowed us to assess reaction times (RTs) even when stopping was successful. We demonstrated shorter RTs in signal-respond (i.e. unsuccessful stopping) than in signal-inhibit (successful stopping) trials, as is predicted by the race models. More importantly, we also demonstrated different pre-signal lateralized readiness potentials between the two types of trials and larger lateralized mu ERD in signal-respond than in signal-inhibit trials, suggesting that voluntarily-generated unimanual preparation affects stopping success. In addition to what is described in the race models of the stop-signal paradigm, the present results therefore demonstrated measures of pre-signal activations that could influence stopping success.     

On the ability to inhibit simple and choice reaction time responses: a model and a method

This article reports four experiments on the ability to inhibit responses in simple and choice reaction time (RT) tasks. Subjects responding to visually presented letters were occasionally presented with a stop signal (a tone) that told them not to respond on that trial. The major dependent variables were (a) the probability of inhibiting a response when the signal occurred, (b) mean and standard deviation (SD) of RT on no-signal trials, (c) mean RT on trials on which the signal occurred but subjects failed to inhibit, and (d) estimated RT to the stop signal. A model was proposed to estimated RT to the stop signal and to account for the relations among the variables. Its main assumption is that the RT process and the stopping process race, and response inhibition depends on which process finishes first. The model allows us to account for differences in response inhibition between tasks in terms of transformations of stop-signal delay that represent the relative finishing times of the RT process and the stopping process. The transformations specified by the model were successful in group data and in data from individual subjects, regardless of how delays were selected. The experiments also compared different methods of selecting stop-signal delays to equate the probability of inhibition in the two tasks.     

Nonselective motor-level changes associated with selective response inhibition: evidence from response force measurements

In the present study, we examined the effects of selective response inhibition on motor production using response force measures within a task that was based on that of Aron and Verbruggen (Psychological Science, 19, 1146–1153, 2008). In each trial, participants were signaled to respond bimanually with the two index fingers or the two middle fingers. After a short delay, a stop signal was sometimes presented, indicating that one of the two finger responses should be withheld. A given response was slowed when the response on the other hand was stopped, replicating a previously observed stopping interference effect. In addition, the given response was also made more forcefully when the response on the other hand was stopped, indicating that the requirement to stop one activated response has global motor-level consequences for other responses that are to be carried out normally.     

The frequentist implications of optional stopping on Bayesian hypothesis tests

Null hypothesis significance testing (NHST) is the most commonly used statistical methodology in psychology. The probability of achieving a value as extreme or more extreme than the statistic obtained from the data is evaluated, and if it is low enough, the null hypothesis is rejected. However, because common experimental practice often clashes with the assumptions underlying NHST, these calculated probabilities are often incorrect. Most commonly, experimenters use tests that assume that sample sizes are fixed in advance of data collection but then use the data to determine when to stop; in the limit, experimenters can use data monitoring to guarantee that the null hypothesis will be rejected. Bayesian hypothesis testing (BHT) provides a solution to these ills because the stopping rule used is irrelevant to the calculation of a Bayes factor. In addition, there are strong mathematical guarantees on the frequentist properties of BHT that are comforting for researchers concerned that stopping rules could influence the Bayes factors produced. Here, we show that these guaranteed bounds have limited scope and often do not apply in psychological research. Specifically, we quantitatively demonstrate the impact of optional stopping on the resulting Bayes factors in two common situations: (1) when the truth is a combination of the hypotheses, such as in a heterogeneous population, and (2) when a hypothesis is composite—taking multiple parameter values—such as the alternative hypothesis in a t-test. We found that, for these situations, while the Bayesian interpretation remains correct regardless of the stopping rule used, the choice of stopping rule can, in some situations, greatly increase the chance of experimenters finding evidence in the direction they desire. We suggest ways to control these frequentist implications of stopping rules on BHT.     

How to stop and change a response: the role of goal activation in multitasking

Multitasking was studied in the stop-change paradigm, in which the response for a primary GO1 task had to be stopped and replaced by a response for a secondary GO2 task on some trials. In 2 experiments, the delay between the stop signal and the change signal was manipulated to determine which task goals (GO1, GO2, or STOP) were involved in performance and to determine whether the goals were activated in series or in parallel. As the delay increased, the probability of responding on stop trials changed very little, but GO2 task reaction times decreased substantially. Such effects are consistent with both a nondeterministic serial model (in which the GO1 goal is replaced by the STOP goal, which is subsequently replaced by the GO2 goal) and a limited-capacity parallel model (in which stopping and GO2 processing occur concurrently) with a capacity-sharing proportion that resembles serial processing.     

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.     

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.     

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.     

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.     

Complex nonverbal response inhibition and stopping impulsivity in childhood stuttering

PurposeThe primary purpose of this study was to examine complex nonverbal response inhibition and stopping impulsivity in children who do (CWS) and do not stutter (CWNS).MethodA total of 30 CWS and 30 CWNS between the ages of 3;1 and 6;0 (years; months) performed the Peg-Tapping Task (PTT; Diamond & Taylor, 1996; Luria, 1966), in which children were required to tap a dowel once when an examiner taps twice and vice versa. The main dependent variables were the number of practice trials, response accuracy, response latency for accurate responses, and the number of extra taps (i.e., tapping more than two times).ResultsThe CWS were less accurate and slower on the PTT than the CWNS, with no differences in the number of practice trials. Furthermore, the CWS, especially boys, produced more extra taps than the CWNS.ConclusionsFindings revealed that preschool CWS have weaknesses in complex response inhibition and stopping impulsivity in the nonverbal domain compared to CWNS. Taken together, these findings along with those of previous studies indicate that CWS may have weaknesses in inhibition and impulsivity in the nonverbal domain as well as the verbal domain, suggesting a domain-general weakness.