The interaction between elapsed time and decision accuracy differs between humans and rats

Abstract

A stochastic visual motion discrimination task is widely used to study rapid decisionmaking in humans and animals. Among trials of the same sensory difficulty within a block of fixed decision strategy, humans and monkeys are widely reported to make more errors in the individual trials with longer reaction times. This finding has posed a challenge for the drift-diffusion model of sensory decision-making, which in its basic form predicts that errors and correct responses should have the same reaction time distributions. We previously reported that rats also violate this model prediction, but in the opposite direction: for rats, motion discrimination accuracy was highest in the trials with the longest reaction times. To rule out task differences as the cause of our divergent finding in rats, the present study tested humans and rats using the same task and analyzed their data identically. We confirmed that rats' accuracy increased with reaction time, whereas humans' accuracy decreased with reaction time in the same task. These results were further verified using a new temporally-local analysis method, ruling out that the observed trend was an artifact of non-stationarity in the data of either species. The main effect was found whether the signal strength (motion coherence) was varied in randomly interleaved trials or held constant within a block. The magnitude of the effects increased with motion coherence. These results provide new constraints useful for refining and discriminating among the many alternative mathematical theories of decision-making.

Different forms of variability could explain a difference between human and rat decision making

“…In the interest of developing a rodent model for perceptual decision-making, we trained rats to perform the random dot motion task [41]. Rats differed from humans and other primates in one key respect: for rats, later decisions are more likely to be accurate [41,42]. The same has also been reported for image discriminations in rats [43], for visual orientation decisions in mice [44], and is found in humans in some other tasks [45][46][47][48].…”

“…Increasing accuracy with response time, as found in rats in this task, was reproduced by a dominance of starting point variability in the model. The fact that rats exhibit this behavioral pattern was only recently appreciated [41][42][43][44], and models developed to explain primate data have yet to be tested on rodent data. One plausible alternative explanation would be reliance on an internal deadline.…”

“…Therefore response bias could account for some of the starting point bias in both species. Response bias is more prevalent in rats than in humans [42]. We don't think this is sufficient to explain the greater starting point variability in rats, however, because correct trials have longer RT than errors even in rat epochs with no bias [42].…”

“…In the random dot motion discrimination task, for example, correct trials of rat subjects are more likely to have longer response times compared to errors (Fig 2A). If we compare the response time of each error trial to the temporally closest correct trial of the same stimulus strength [42], we see that on average, correct trials have longer response times than neighboring error trials of the same stimulus strength ( Fig 2B). This trend is found in most individual experiments on rats ( Fig 2C).…”

“…. Psychophysical threshold is defined as the motion coherence at which accuracy is 70%, based on a psychometric fit of accuracy vs. coherence from the same experiments [42]. Symbols indicate population mean, error bars indicate population SD.…”