Abstract

Perceptual decisions are based on the temporal integration of sensory evidence for different states of the outside world. The timescale of this integration process varies widely across behavioral contexts and individuals, and it is diagnostic for the underlying neural mechanisms. In many situations, the decision-maker knows the required mapping between perceptual evidence and motor response (henceforth termed “sensory-motor contingency”) before decision formation. Here, the integrated evidence can be directly translated into a motor plan and, indeed, neural signatures of the integration process are evident as build-up activity in premotor brain regions. In other situations, however, the sensory-motor contingencies are unknown at the time of decision formation. We used behavioral psychophysics and computational modeling to test if knowledge about sensory-motor contingencies affects the timescale of perceptual evidence integration. We asked human observers to perform the same motion discrimination task, with or without trial-to-trial variations of the mapping between perceptual choice and motor response. When the mapping varied, it was either instructed before or after the stimulus presentation. We quantified the timescale of evidence integration under these different sensory-motor mapping conditions by means of two approaches. First, we analyzed subjects’ discrimination threshold as a function of stimulus duration. Second, we fitted a dynamical decision-making model to subjects’ choice behavior. The results from both approaches indicated that observers (i) integrated motion information for several hundred ms, (ii) used a shorter than optimal integration timescale, and (iii) used the same integration timescale under all sensory-motor mappings. We conclude that the mechanisms limiting the timescale of perceptual decisions are largely independent from long-term learning (under fixed mapping) or rapid acquisition (under variable mapping) of sensory-motor contingencies. This conclusion has implications for neurophysiological and neuroimaging studies of perceptual decision-making.

Highlights

  • A hallmark of perceptual decision-making is the integration of evidence for different states of the world [1]

  • While many studies of non-sensory effects in perceptual decision-making have focused on strategic adjustments of the decision threshold that terminates the decision process [3,6,8,9,10], only few previous studies have investigated direct top-down effects on the evidence integration process per se, as indicated by the integration timescale [11,12,13,14]

  • We found that integration timescales were generally shorter than the maximum stimulus duration, and shorter than the timescale required to maximize the fraction of correct choices in the task

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Summary

Introduction

A hallmark of perceptual decision-making is the integration of evidence for different states of the world [1]. While many studies of non-sensory (top-down) effects in perceptual decision-making have focused on strategic adjustments of the decision threshold that terminates the decision process [3,6,8,9,10], only few previous studies have investigated direct top-down effects on the evidence integration process per se, as indicated by the integration timescale [11,12,13,14] Two of these studies were conducted in human observers [11,13] whose integration mechanisms may differ from those of other species [15]. We examined the effect of one important top-down factor that has not been previously examined: knowledge of sensory-motor contingencies

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