Visual psychophysics and limits of visual discrimination performance in freely behaving mice

Abstract

Studying the temporal dynamics of perceptual decisions offers key insights into the cognitive processes contributing to it. Conducting such investigation in a genetically tractable animal model can facilitate the subsequent unpacking of the mechanistic basis of different stages in perceptual dynamics. Here, we investigated the time course as well as fundamental psychophysical constants governing visual perceptual decision-making in freely behaving mice. We did so by analyzing response accuracy against reaction time (i.e., conditional accuracy), in a series of 2-AFC orientation discrimination tasks in which we varied target size, luminance, duration, and presence of a foil. Our results quantified two distinct stages in the time course of mouse visual decision-making - a sensory encoding stage, in which conditional accuracy exhibits a classic tradeoff with response speed, and a subsequent short term memory-dependent stage in which conditional accuracy exhibits a classic asymptotic decay following stimulus offset. We estimated the duration of visual sensory encoding as 200-320 ms across tasks, the lower bound of the duration of short-term memory as ~1700 ms, and the briefest duration of visual stimulus input that is informative as [≤]50 ms. Separately, by varying stimulus onset delay, we demonstrated that the conditional accuracy function and RT distribution can be independently modulated, and found that the duration for which mice naturally withhold from responding is a quantitative metric of impulsivity. Taken together, our results establish a quantitative foundation for investigating the neural circuit bases of visual decision dynamics in mice. SIGNIFICANCE STATEMENTThis study presents a quantitative breakdown of the time course of visual decision-making in mice during naturalistic behavior. It demonstrates parallel stages in mouse visual perceptual decision dynamics to those in humans, estimates their durations, and shows that mice are able to discriminate well under challenging visual conditions - with stimuli that are brief, low luminance, and small. These results set the stage for investigating the neural bases of visual perceptual decision dynamics and their dysfunction in mice.