Supplementary Experimental Procedures: Participants

participated in Experiments 1-3, and an additional two (1 female, ages 25 and 20) participated in Experiments 1 and 3. Three of these eight completed Experiment 3 first, and the rest did Experiment 3 after at least two sessions of the other experiments. Half of these subjects were naive to the purposes of the study. Six subjects (1 female, age range 20-33) participated in Experiment 4, and only one of them (AH) participated in any of the other experiments. All subjects had normal or corrected-to-normal vision. Experiment 1: Visuomotor Synchronization The displays for all four experiments involved the same components (depicted in Figure 1) and were programmed using PsychoPy [s1]. The luminance of the background and the outer reference bars were approximately 0.2 cd/m2 and 4.6 cd/m2, respectively. On each trial, the luminance of the inner bar was chosen randomly from four values: 0.3, 7.0, 27.4, and 120.0 cd/m2. Before beginning each session, subjects dark-adapted for 5 minutes. Each session (between 224 and 256 trials) lasted approximately 25 minutes. Subjects sat 57 cm away from a CRT refreshing at 120 Hz and fixated a red dot (0.2 deg diameter) at the center of the screen. A 3.0 x 0.2 deg bar rotated about the fixation poin