Intermittent-viewing blocks

Each block consisted of six trials, with each trial consisting of: 2 s instruction screen, 2 s fixation screen, and then for 60 s there was a repeating sequence of 1.5 s presentation of an image followed by a blank screen (with only a fixation cross) of variable duration (64 s total trial duration). Within each trial, 1 of 3 possible durations was used for the blank period: 570 ms, 970 ms, or 1570 ms. These durations were chosen based on previous studies showing that varying the blank-period duration changes the perceptual reversal rate^17,19,20; specifically, we were interested in using blank durations that resulted in gradually increased stabilization of the percept. The subject was instructed to fixate on the cross at the center of the screen throughout the task and indicate their percept each time the image appears on the screen and any time their percept switches while the image is on the screen. Each ambiguous image was presented in 3 trials within each block. Because there were three possible blank-period durations and two images, each block consisted of the same six types (2 images × 3 durations) of trials in a pseudorandomized order. The total block time was 7.4 min.