Leveling the Field for a Fairer Race between Going and Stopping: Neural Evidence for the Race Model of Motor Inhibition from a New Version of the Stop Signal Task

Abstract

The stop signal task (SST) is the gold standard experimental model of inhibitory control. However, neither SST condition–contrast (stop vs. go, successful vs. failed stop) purely operationalizes inhibition. Because stop trials include a second, infrequent signal, the stop versus go contrast confounds inhibition with attentional and stimulus processing demands. While this confound is controlled for in the successful versus failed stop contrast, the go process is systematically faster on failed stop trials, contaminating the contrast with a different noninhibitory confound. Here, we present an SST variant to address both confounds and evaluate putative neural indices of inhibition with these influences removed. In our variant, stop signals occurred on every trial, equating the noninhibitory demands of the stop versus go contrast. To entice participants to respond despite the impending stop signals, responses produced before stop signals were rewarded. This also reversed the go process bias that typically affects the successful versus failed stop contrast. We recorded scalp electroencephalography in this new version of the task (as well as a standard version of the SST with infrequent stop signal) and found that, even under these conditions, the properties of the frontocentral stop signal P3 ERP remained consistent with the race model. Specifically, in both tasks, the amplitude of the P3 was increased on stop versus go trials. Moreover, the onset of this P3 occurred earlier for successful compared with failed stop trials in both tasks, consistent with the proposal of the race model that an earlier start of the inhibition process will increase stopping success. Therefore, the frontocentral stop signal P3 represents a neural process whose properties are in line with the predictions of the race model of motor inhibition, even when the SST's confounds are controlled.

Explaining dual-action benefits: Inhibitory control and redundancy gains as complementary mechanisms.

“…Diesburg & Wessel, 2021); it provides a structural, model-inherent explanation of dual-action benefits (i.e., in single-, but not in dual-action trials, all responses are delayed by the pause process); and relatedly, it is compatible with, but does not require additional assumptions like shared capacity. Even more importantly, however, it can parsimoniously explain why manual dual-action benefits in the RTs disappeared in Experiment 2, but false-positive manual errors on single-vocal trials persisted: a fixed sequence of conditions (that is also known in advance as it is instructed) means that even if—as the inhibitory coding framework would predict—inhibition in single-action trials is still necessary given the nonreductive response set, it is now perfectly predictable —thus, an initial “hold-your-horses”-reaction is highly unlikely (note that Diesburg & Wessel, 2021, explicitly suggest that predictable stopping does not require pausing; also see Dykstra et al, 2020). Without a nonspecific “pause” stage, the instructed response modality is no longer slowed down when a single action is required, eliminating the relative RT advantage for dual-action trials; at the same time, countermanding—even when expected— can still fail, which would account for the reduced, but persistent level of false-positive responses in Experiment 2.…”

The Pause-then-Cancel model of human action-stopping: Theoretical considerations and empirical evidence

“…We propose that successful stopping and the activation of the Cancel process does not require the prior activation of the Pause mechanism. In fact, recent work demonstrated that participants can perform a task with a stop signal on every trial, producing approximately 50% successful stops (Dykstra et al, 2020). Despite frequent stop-signals, the P3, a signature of motor inhibition, was still elicited and onset earlier for successful than for failed stops.…”

“…Studies of the hyperdirect pathway facilitated Pause process should account for the pre-Pause perceptual processes and the co-occurrence of reorienting and inhibition inherent in the Pause mechanism. Researchers interested particularly in the indirect pathway-related Cancel process should consider how to design tasks that reduce the likelihood of the Pause process being implemented; using a SST with frequent stop-signals might accomplish this (Dykstra et al, 2020), but could possibly affect the strategies participants use to complete the task. Critically, because SSRT does not seem to align with these underlying inhibitory processes, researchers who collect behavioral SST data should strongly consider collecting a simultaneous neurophysiological measure of inhibition or single-trial measure of EMG from the responding muscle when time and resources allow.…”

β-Bursts Reveal the Trial-to-Trial Dynamics of Movement Initiation and Cancellation

“…Two hundred and thirty-four healthy adult humans (mean age: 22.7, SEM: 0.43, 137 female, 25 left-handed) from the Iowa City community participated in the study, either for course credit or for an hourly payment. The majority of these datasets have been previously published as part of other studies, none of which focused on ␤-bursting (Dutra et al, 2018;Wessel, 2018a,b;Dykstra et al, 2019;Waller et al, 2019;Wessel et al, 2019). All procedures were approved by the local ethics committee at the University of Iowa (IRB 201511709).…”