CONCLUSIONS

Human discrimination of time intervals in the supra-second domain is characterized by (i) a relatively low accuracy, a,d for longer durations, (ii) a systematic tendency to underestimation of earlier durations w.r.t. more recent ones, reflecting an asymmetry of the discrimination function. This asymmetry can be explained by a model of internal time representation based on lossy integrators. The results contribute to a unified interpretation of experimental data on human "time perception" obtained with two different methods, namely, pair-wise comparison and reproduction of time intervals.

ABSTRACT

Interval timing, anticipation of periodic events signalled by a time marker, has been explained by a separate pacemaker-counter clock. But recent theoretical work suggests that memory strength can act as clock. The way that memory strength declines with time can be inferred from the properties of habituation and the same process provides a parsimonious explanation for proportional timing, the Weber-law property and several other properties of interval timing.

"The aforementioned psychological factors definitely influence the processing of duration. However, a specific neural timing mechanism—influenced by the aforementioned factors—nevertheless, could account for our ability to accurately process temporal intervals. Especially for shorter durations up to a few seconds, humans can accurately synchronize their movements to regular beats (Mates et al. 1994), discriminate tones with different durations (Rammsayer & Lima 1991) or reproduce presented intervals (Eisler and Eisler 1994). Yet, there is no consensus as to which temporal mechanisms account for these temporal-processing abilities. Over the last decades, the most successful models for such a mechanism have been variants of a pacemaker–accumulator clock, where an oscillator (a pacemaker) produces a series of pulses (analogous to the ticks of a clock) and the number of pulses recorded over a given timespan represents experienced duration (Poppel 1971; Church 1984; Treisman et al. 1990; Meck 1996; Zakay and Block 1997). However, competing models assume neuronal system properties for encoding duration not related to a simple pacemaker–accumulator system (Matell and Meck 2004; Wackermann and Ehm 2006; Karmarkar and Buonomano 2007), or they propose that memory decay processes are involved in time perception (Staddon 2005; Wackermann & Ehm 2006). Related to this unsolved issue, the question of which areas of the brain process duration has also not yet been answered definitely. Among other regions, most prominently, the cerebellum (Ivry & Spencer 2004), the right posterior parietal cortex (Bueti et al. 2008a), the right prefrontal cortex (Rubia & Smith 2004; Lewis & Miall 2006) as well as fronto-striatal circuits (Harrington et al. 2004a; Hinton & Meck 2004) have been implicated as the neural substrates of a potential timekeeping mechanism