Abstract
Many perceptual decision making models posit that participants accumulate noisy evidence over time to improve the accuracy of their decisions, and that in free response tasks, participants respond when the accumulated evidence reaches a decision threshold. Research on the neural correlates of these models' components focuses primarily on evidence accumulation. Far less attention has been paid to the neural correlates of decision thresholds, reflecting the final commitment to a decision. Inspired by a model of bistable neural activity that implements a decision threshold, we reinterpret human lateralized readiness potentials (LRPs) as reflecting the crossing of a decision threshold. Interestingly, this threshold crossing preserves signatures of a drift-diffusion process of evidence accumulation that feeds in to the threshold mechanism. We show that, as our model predicts, LRP amplitudes and growth rates recorded while participants performed a motion discrimination task correlate with individual differences in behaviorally-estimated prior beliefs, decision thresholds and evidence accumulation rates. As such LRPs provide a useful measure to test dynamical models of both evidence accumulation and decision commitment processes non-invasively.
Highlights
Decision making has traditionally been described as a process of evidence accumulation up to an abstract decision threshold, in which accumulation over time increases the chance of an accurate response (e.g., [1])
It is important to examine the area between curves for the early phase of the lateralized readiness potentials (LRPs), rather than the height of its peak, because our model showed that this early phase is most sensitive to the differences between conditions
We propose that the early part of the LRP does reflect evidence accumulation, whereas variations in the later, ballistic part, on which Rinkenauer and colleagues focus, reflect primarily the adaptation of speed-accuracy tradeoffs (SATs)
Summary
Decision making has traditionally been described as a process of evidence accumulation up to an abstract decision threshold, in which accumulation over time increases the chance of an accurate response (e.g., [1]). We show that these predictions are satisfied by the lateralized readiness potential (LRP), a difference wave between centrally located scalp potentials that routinely accompanies manual responding. This emphasis on decision threshold activity turns out to provide a useful methodological approach to studying the evidence accumulation process thought to precede decision threshold-crossing. A canonical evidence accumulation model for response-time tasks is the drift diffusion model (DDM; [4]). In the DDM, the presentation of a stimulus drives a noisy evidence-accumulation process until it reaches one of two decision thresholds. His/her response time (RT) is determined by the time it takes to reach this decision threshold, plus the time taken for non-decision processes (e.g., perceptual and motor delays)
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