Abstract
We found that a novel phenomenon on the high-speed (400 Hz) flickering stimuli that if the counterphase-flickering pattern (e.g. square-wave grating) is immediately switched to another flickering pattern, a luminance-averaged pattern around the time of transition can be stably perceived. The purpose of this study is to investigate the temporal property of this phenomenon. In the experiment, stimuli were presented at the center of the screen within a square region (2 x 2 deg) surrounded by a pseudo gray background (a 1-pixel checkerboard). Stimuli consisted of two rectangular flickering patterns: Uniform squares of black and white (FU) and counterphase-flickering horizontal/vertical square-wave gratings (FG). Flicker frequency was 400 Hz (i.e., frame duration was 1.25 ms), implemented by a high-speed DLP projector (LightCommander, TI Inc.). The stimuli were presented in order of FU, FG and FU without ISI. The duration of FU was fixed at 200 ms while that of FG was randomly selected from 9 durations (2.5 – 200 ms). Participants (n = 5) were asked to discriminate the orientation of the grating by 2-AFC in one experimental session, and to answer the perceived number of the gratings by 3-AFC (zero, one, or two) in the other session. The orientation discrimination performance was improved with longer FG duration, and average percent correct reached 75% around 10 ms. As for the perceived grating number, participants perceived no grating when FG duration was shorter than 10 ms, one grating with FG duration between 10 and 100 ms, and two gratings with FG duration longer than 100 ms. It suggests that the abrupt switch between 400-Hz flickering stimuli can be detected with a stable perception of a oriented pattern so long as two transitions do not occur within 10 ms and the pattern can be perceived at each transition with FG duration over 100 ms.
Meeting abstract presented at VSS 2015