Asymmetry of the discrimination function for temporal durations in human subjects

Ten human subjects were comparing durations of pairs of visual stimuli in a two-way forced-choice task. Mean durations of presented time intervals were -3 s ("short") or -6 s ("long"); the duration ratio was varied at nine levels. The Weber fractions for the short and long durations were approximately equal, -0.22. The ratio of subjective equality was almost exactly unity for the short durations, but it was significantly reduced (-0.76) for the long durations. This asymmetry of the discrimination function indicates time-dependent change of internal representations of past durations, and is well compatible with the "dual klepsydra model". Model-based estimates of the internal time representation loss rate, derived from the present data, are in a good agreement with values obtained from earlier studies on duration reproduction.