Page 38 - It' about time: Studying the Encoding of Duration

An investigation of the spatial selectivity of the duration after-effect Materials and stimuli. For the non-eyetracking runs of the experiment, materials were the same as in Experiment 1 & 2. For the runs including eyetracking, a different setup was used to accommodate the use of our eye-tracker. Stimuli were presented on the same monitor but were controlled by a Dell OptiPlex 7040 workstation running Windows 10 and Matlab 2015b. Display luminance for all stimuli was matched for both setups, with all deviations <0.05 cd/m2. Average luminance values are reported for this experiment. All timings were 2 evaluated using a dual channel oscilloscope. Gaze position was measured using an EYE TRIBE tracker sampling at 30 Hz, controlled using the PyGaze software package and eye tribe toolbox for Matlab (Dalmaijer, 2014; Dalmaijer et al., 2014). Finally, we used a chin- and headrest, to increase head stability. All stimuli were equal to those used in Experiment 1 (Gaussian blob: r = 0.75°, 76% peak Michelson contrast) and were accompanied by a central fixation dot (64.2 cd/m2; 0.50 x 0.50°) presented on a gray background (8.29 cd/m2). Once more, an ASA staircase procedure was used to set the duration of the auditory stimulus (M = 291.29 ms, SD = 57.87 ms). All other presentation conditions and timings were identical to experiment 1. Procedure. The procedure was similar to that of the first experiment. Participants adapted to a 100 repetitions of a visual stimulus lasting 160 ms or 640 ms. All stimuli were presented 8° from the center of the screen at 4 different possible angles (45, 135, 225, and 315 degrees; see Figure 4). The location of the adaptation stimuli was counterbalanced across these 4 locations, with a single location being used for each participant. For each participants test stimuli were always presented at one of three possible locations: At the adapted location, in the horizontally adjacent quadrant, or in the vertically adjacent quadrant. This resulted in two adapter-test distances (center-to-center distance: 0, 11.31°), with the non-zero distance being presented either within- or between- hemifield (Figure 4). For the eyetracking group, the procedure was expanded to include gaze measurements. At the start of each experiment we tested the fidelity of the gaze signal by running two test 9-point calibrations. In case the eyetracking signal was too poor to complete calibration, another unrelated experiment was conducted instead. Three people were excluded via this procedure. After this initial check, we started the experiment. At the start of each block, participants were (re)calibrated to assure good calibration. Additionally, at the start of each 37