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ELSC-ICNC Seminar - Michael Shadlen

Published by Admin in Behavioral Science
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Michael Shadlen MD, PhD, Professor and HHMI Investigator, Department of Physiology&BiophysicsOn the topic of:"Integration of prior probability and evidence in a neural mechanism of decision making"Abstract:I will describe two unpublished studies that elaborate the themes from the Heller lecture. (1) I will introduce a novel characterization of neural response variance and apply it to neural recordings from the parietal cortex during perceptual decision-making. The method identifies between-trial variance and within-trial correlations of spike rates that a neuron would be expected to produce were it not for irregular spiking. These measures could be a valuable tool for constraining neural mechanisms in a variety of experimental contexts. In our data, the tool shows that the firing rates of LIP neurons on single trials obey dynamics consistent with drift-diffusion, suggesting that the neuron represents the temporal integration of noisy evidence during decision formation. (2) I will explain how knowledge of prior probability affects decision-making. Not surprisingly, if a decision-maker knows that one alternative is more likely than another, choices and reaction times reflect this bias. The neural mechanism exploits the interplay between firing rate, probability and elapsed time. Surprisingly, prior probability—which is fixed for the duration of a decision and indeed for hundreds of trials—is represented by a time-varying signal in the brain. This dynamic signal is added to the accumulation of evidence to bias decisions. Thus we return to the theme of time and beliefMore videos from ELSC at http://www.youtube.com/elscvideo

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