Comparing the speed of action initiation and action inhibition

Abstract

We often need to swiftly abort a prepared response at the last moment before it is initiated. Our ability to abort a planned response is thought to be a fundamental facet of action control that is distinguished by its rapid speed, and is enabled by a specialized neural mechanism. This narrative has, however, largely been established based on experiments in which there is much greater urgency to abort an action than there is to generate an action. Here, we demonstrate that, under conditions of matched urgency, the speed at which participants are able to abort an action is comparable to the speed at which they can initiate an action. Our results challenge the prevailing view that stopping behaviors have a privileged status. We suggest, instead, that action initiation may often be systematically delayed to allow time to abort an action if needed.

Dissociable habits of response preparation versus response initiation

“…Although these are viewed as equivalent under the stimulus-response view of habits, it is possible that they might correspond to distinct habits. This would be consistent with recent evidence in motor control showing that preparation and initiation of actions are independent processes [19][20][21] with distinct neural bases [22][23][24][25][26] . If habitual preparation and habitual initiation of a response are indeed distinct forms of habit, rather than two manifestations of the same underlying habit, then it ought to be possible to form one habit and not the other.…”

“…We confirmed this apparent lack of habit in the Withholding group in two distinct ways. We compared the time course by which the probability of generating a response declined over time (Figure 2E, red solid line) against an estimated time course for inappropriately generating a response if behavior was not habitual, which we based on the time course of generating responses to non-revised stimuli (which still required a response) 20 . We did this by inverting and re-scaling the time course for non-revised stimuli (Figure 2D, orange dotted line; Methods).…”

“…In this model, we assumed that the decision to commit to generating a response or not occurred at a random time, analogous to the time of response preparation in the previous model (Figure 2J). The outcome of this event determined whether or not a response would actually be initiated at the prescribed time of responding 20 . The no-habit model was strongly favored for data pooled across all participants in both the Withholding group (∆AICnon-habit -habit = -103.73) and the Withholding-minimum group (∆AICnonhabit -habit = -189.50).…”

Habitual responses are retrieved from memory, not triggered reflexively

“…Since it has been shown that RT may not accurately reflect how fast a response can be made to a cueing stimulus (Du, Forrence, Metcalf, & Haith, 2022;Haith, Pakpoor, & Krakauer, 2016), we also examined the set-size effect under the forced-reaction-time condition, as described for the familiarization task. Again, participants first performed the 4-element task for 3 blocks of 96 trials, followed by performing the 8-element task for 6 blocks of 96 trials.…”

“…To more precisely compare behavior across conditions, we quantified the response speed under the forced-reaction-time condition using a previously-established model (Du, Forrence, et al, 2022;Haith et al, 2016). We assumed that participants became able to select the correct response at a random time T ~ N(μ, σ 2 ).…”