Strategic and dynamic temporal weighting for perceptual decisions in humans and macaques

ABSTRACT

Perceptual decision-making is often modeled as the accumulation of sensory evidence over time. Recent studies using psychophysical reverse correlation have shown that even though the sensory evidence is stationary over time, subjects may exhibit a time-varying weighting strategy, weighting some stimulus epochs more heavily than others. While previous work has explained time-varying weighting as a consequence of static decision mechanisms (e.g., decision bound or leak), here we show that time-varying weighting can reflect strategic adaptation to stimulus statistics, and thus can readily take a number of forms. We characterized the temporal weighting strategies of humans and macaques performing a motion discrimination task in which the amount of information carried by motion stimulus was manipulated over time. Both species could adapt their temporal weighting strategy to match the time-varying statistics of the sensory stimulus. When early stimulus epochs had higher mean motion strength than late, subjects adopted a pronounced early weighting strategy, where early information was weighted more heavily in guiding perceptual decisions. When the mean motion strength was greater in later stimulus epochs, in contrast, subjects shifted to a marked late-weighting strategy. These results demonstrate that perceptual decisions involve a temporally flexible weighting process in both humans and monkeys, and introduce a paradigm with which to manipulate sensory stimuli in decision-making tasks.

SIGNIFICANCE STATEMENT During decision-making, the weight assigned by subjects to sensory information over time is not necessarily constant. Such time-varying weighting is often interpreted as a signature of a particular decision-making model (e.g., higher weighting of early stimulus information is consistent with a bounded accumulation process). Temporal weighting may also result, however, from a strategic reweighting of the stimulus evidence itself that takes place before and/or independent of a decision-making mechanism. Here we use a psychophysical reverse correlation paradigm to both measure and manipulate temporal weighting behavior. We demonstrate that both humans and macaques adopt weighting strategies that are flexible, consistent with dynamic reweighing of the sensory stimulus.