Illustration of the oddball procedure.

a: Display sequence in one sample trial. On each trial a pseudo-randomized stream of 5 to 15 stimulus displays was shown, each interspersed with a randomly jittered blank inter-stimulus interval. A minimum of three standard displays containing green dots were presented before the first oddball occurrence made up of red dots and at least one standard followed an oddball on each trial. At the end of each trial sequence participants indicated the perceived number of red dots and judged its temporal duration relative to the standards. b: Experimental parameters for long stimulus durations (experiments 1 & 3), short stimulus durations (experiments 2 & 4) and long stimulus duration around the PSE (experiment 5). In all five experiments oddball number and duration were independently varied, in order to measure both enumeration and perceived duration on different temporal scales (around one second durations for temporal expansion and 100 ms durations for compression). Standard displays were always presented for a fixed duration and contained a pseudo-random number of items. In the fifth experiment temporal expansion was only examined for one oddball duration at the point of its subjective equality to standard duration.