Ordinal Judgments in the Rat: An Understanding of Longer and Shorter for Suprasecond, but Not Subsecond, Durations

An emerging corpus of clinical and neuroimaging data suggests that subsecond and suprasecond durations are represented via 2 distinct mechanisms in humans; however, surprisingly, behavioral data to this effect are lacking. In our first experiment, we perform the first systematic exploration of subsecond and suprasecond timing within the same session in nonhuman subjects. Rats were trained to judge the relative duration of 2 sequential stimuli, responding on one lever if the first stimulus was longer or on a second lever if the converse was true. Our data provide strong evidence of an abstract understanding of longer and shorter for durations in the suprasecond range, whereas responding was at chance levels for durations in the subsecond range. Data from a second experiment reveal that this pattern is not due to an inability to time subsecond signals, as rats respond systematically in subsecond and suprasecond bisection tasks. Together, our results provide the first clear behavioral evidence of a discontinuity in the mental time line. These data from rats are discussed in light of similar findings of a discontinuity in the mental number line in human infants.