Discontinuity in the perception of sub-seconds intervals

A classical distinction in the time perception field is between intervals above and below 1 sec (Grondin, 2010), which seem to be processed by two different systems. Sub-second intervals are mainly processed by automatic timing, which does not require attentional modulation, whereas supra-second durations are under the control of higher cognitive functions such as attention and working memory (see Lewis & Miall, 2003, for a review). Here, we aimed to further explore the behavioral pattern of estimation and reproduction of brief sub-second intervals. Thirty-two university students (28 females, mean age=24.19 \ub1 2.40 years) performed a temporal discrimination task (TDT) and a temporal reproduction task (TRT) with sub-seconds intervals. In the TDT, participants were required to judge whether the duration of a target stimulus (light-blue rectangle) appearing on the screen was shorter or longer than that of a reference stimulus (yellow rectangle). The duration of the reference cue was fixed across the trials (400 ms), whereas the duration of the target ranged from 200 to 600 ms in steps of 100 ms, with the exception of 400 ms. In the TRT, participants were required to reproduce the duration of a reference stimulus (yellow rectangle) which remained on the screen for 200, 300, 400, 500, or 600 ms, after the presentation of a sound cue. This sound cue activated a virtual clock, which participants had to stop by pressing a button when a similar duration had passed. Data were analyzed in terms of probability to respond longer for the TDT and computing the coefficient of variation (CV, the ratio between the standard deviation and the mean) for each duration in the TRT (Lewis & Miall, 2009). In the TDT, participants had no difficulties to discriminate 200 and 300 ms from the 400 ms stimulus reference. However, the probability to respond longer to the 500 ms stimuli was exactly at chance. In the TRT, a similar CV was observed for 200 and 300 ms trials and for 500 and 600 ms trials, with a significant difference between the shorter (200-300 ms) and the longer intervals (500-600 ms). The CV of 400 ms was set in the middle between shorter and longer intervals. Taken together these results suggest that sub-second durations are processed in a segmented rather than a linear mode, with a turning point around 400 ms