Academic journal article Attention, Perception and Psychophysics

Response Inhibition during Perceptual Decision Making in Humans and Macaques

Academic journal article Attention, Perception and Psychophysics

Response Inhibition during Perceptual Decision Making in Humans and Macaques

Article excerpt

Published online: 5 December 2013

© Psychonomic Society, Inc. 2013

Abstract 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.

Keywords Decision making · Inhibition · Eyemovements

The goal of this study was to investigate whether the mecha- nisms responsible for choosing responses share resources with or are independent from the mechanisms responsible for inhibiting responses. To do so, we designed a paradigm that unifies two major approaches employed in the cognitive sci- ences to study how we choose among alternative responses and how we inhibit responses. The findings provide evidence that perceptual choice and response inhibition are independent processes, and they establish a foundation to develop cogni- tive models and neurophysiological recordings within the well-understood visual saccadic system.

Perceptual categorization is usually studied using two- alternative forced choice tasks and is described by sequential- sampling models like the drift diffusion and competing- accumulator models (reviewed by Bogacz, 2007; Gold & Shadlen, 2007; Smith & Ratcliff, 2009). The premise of sequential-sampling models is that evidence about the stimulus category accumulates through repeated sampling. A categorical choice is committed when the accumulated evidence reaches a criterion. Versions of these models account well for accuracy and response times (RTs) in choice tasks.

Response inhibition is often studied using stop signal (countermanding) tasks, and the race model of response inhibi- tion describes how we initiate or withhold a prepared response (reviewed by Schall & Godlove, 2012; Verbruggen & Logan, 2009). During a stop signal task, a subject is cued to respond to a primary stimulus on each trial, but on some trials a subsequent stimulus-the stop signal-is presented, instructing the subject to withhold the response to the primary stimulus. The premise of the race model is that the outcome of stop signal trials is the result of a race between stochastically independent GO and STOP processes. If the STOP process finishes first, the response is withheld (a canceled, or signal-inhibit, trial), whereas if the GO process finishes first, the response is initiated (a noncanceled, or signal-respond, trial). The race model accounts for inhibition probabilities and RTs and allows for estimation of the stop signal reaction time (SSRT), which is the time needed to react to the stop signal by canceling the response.

Most stop signal tasks use a primary stimulus that requires a choice response. However, few studies have manipulated the perceptual discriminability of the choice stimulus, and none have done so parametrically. One human study used a primary buttonpress task that required deciding whether a visual stim- ulus appeared on the left or the right side of a display screen (Logan, 1981), and choice difficulty was varied by presenting the stimulus near or far from the center of the screen. …

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