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. Author manuscript; available in PMC: 2015 Jan 20.
Published in final edited form as: Brain Lang. 2014 Sep 29;138:27–37. doi: 10.1016/j.bandl.2014.09.003

Figure 1. Psychophysical protocol.

Figure 1

a. Speed discrimination task. Top. Gratings (5° in diameter, 0.5 c/° spatial frequency) were presented at the center of the screen in two 375-ms long intervals separated by an inter-stimulus interval of 250 ms. Gratings in both intervals had the same contrast (either 16 or 24%). Bottom. On every trial one of the stimuli drifted from right to left at 38 °/s (base speed), the other had a higher drift speed (base speed + delta-s). Participants indicated the temporal interval containing the faster grating. The speed difference between the two gratings (delta-S) was adjusted on each trial by an adaptive staircase procedure to measure the 75% speed discrimination. b. Contrast detection task. Top. Gratings (5° in diameter, 0.5 c/° spatial frequency) were presented at the center of the screen in two 375-ms long intervals separated by an inter-stimulus interval of 250 ms. Only one randomly-chosen interval contained the target grating (first in the figure). Bottom. Gratings drifted right to left at 38 °/s. Participants indicated the temporal interval containing the target grating with a key press. The contrast of the target grating (delta-c) was changed on each trial by an adaptive staircase procedure to measure the 75% contrast detection threshold (QUEST; Pelli, 1985).