To investigate the effects of voluntary blinking, observers were instructed to intentionally blink while observing stimuli. However, this instruction could influence their natural, spontaneous blinking behavior. To minimize potential confounding effects, the experiment was divided into two separate sessions conducted on different days. In Session 1, observers were informed that an eye camera would be set up to monitor their gaze position. Then, in Session 2, they were asked to blink voluntarily in specific conditions. After completing Session 2, they were notified that their blinking had been measured during the experiment. They were then asked to confirm the use of their blink data for the analysis.
Session 1 was designed to investigate the effects of spontaneous blinking and blackout. The main stimulus condition in this session was the b-CFS condition. Trials for this and other stimulus conditions were initiated by the observer's button press. The Mondrian suppressor was presented first to establish steady suppression, and the target was presented 0.5 s later. The target contrast was ramped up from zero to a maximum of 0.8 over 3.0 s, maintained at that level for 4.0 s, and then ramped down over another 3.0 s (for a total duration of 10.0 s). The suppressor was turned off 0.5 s after the target offset, followed by dynamic white noise (7.10° × 7.10°, 10 Hz) for 1.5 s to minimize carryover effects such as afterimages. Observers were asked to indicate the target orientation (clockwise or counterclockwise) as soon as possible using a CT3 response box, where pressing the right button corresponded to clockwise responses and the left button to counterclockwise responses. There was no time limit for the observers’ responses. The time required for orientation discrimination (discrimination response time, DRT), used as an index of the time required for a perceptual alternation, was measured from target onset to the observer's response. Auditory feedback was provided at the end of each trial. The trials in the b-CFS condition were classified into no-blink and spontaneous-blink trials according to whether a blink was observed at a specific time (see Trial classification).
In Session 1, blackout and no-suppression conditions were included, which were variations of the b-CFS condition. In the blackout condition, a brief physical blackout was introduced by temporarily darkening the stimulus displays. This blackout began 1.0 s after the target onset and lasted 0.3 s, a duration chosen to match the typical length of a spontaneous blink (
Stern et al., 1984). During this period, both the target and the Mondrian suppressor were not visible, effectively interrupting the visual input. The no-suppression condition was included to measure DRT in the absence of any visual suppression. In this condition, only the target was presented without the Mondrian suppressor, allowing the observer to view the target directly from the moment it appeared. This condition allowed us to assess how quickly observers could discriminate the target's orientation when no visual suppression was present.
Session 2 was designed to investigate the effect of voluntary blinking. The stimulus conditions consisted of the voluntary-blink condition and three control conditions, which were variations of the b-CFS condition. In the voluntary-blink condition, observers were instructed to blink immediately after a cue. The cue involved a color change in the fixation pattern from white to red (x = 0.642, y = 0.337, 12 cd/m²) and was presented 1.0 s after the target onset. The three control conditions were included to examine the effects of the mere presence of the cue and conducting dual tasks (target discrimination and intentional blinking). In these control conditions, both the instructions to observers—whether to respond to or disregard the cue—and the presentation of the cue were systematically manipulated. Specifically, in one control condition, observers were instructed to blink in response to the cue, but the cue was not presented. In another condition, observers were instructed to disregard the cue, and the cue was presented. In the final condition, observers were instructed to disregard the cue, and the cue was not presented. Prior to each trial, observers were informed whether they were supposed to respond or disregard the cue.
Experiments were conducted in a dark room. Before the experiment, the observers were dark-adapted for 5 min and then light-adapted to the background field for 2 min. All stimulus conditions in both Sessions 1 and 2 were tested 36 times.