Abstract
In a variant of Troxler's filling-in, nearly equiluminant, chromatic flickering stimuli fade away quickly. We found that a series of sounds synchronized with such a stimulus aids its recovery, and delays its fading. Two red disks (2.5o dia.) centered 5.2o left and right of fixation were alternately flashed for 17 ms each (187 ms inter-stimulus interval, or ISI) on an equiluminant green background at 2.5 Hz for 3 min. The background filled in perceptually. On trials that followed, a 14.9 s re-adaptation phase was followed by a 6.4 s long pairing of one of the flickers with a 11 dB 2 ms long, spatially non-localized click. Subjects (Ss; n=5) had to pick the more visible or visually salient disk regardless of sound. They chose the one coincident with the sound on 81% (range: 73–90%) of trials. General arousal or eye movements cannot explain the data since they would make both stimuli equally visible. Randomly flickered stimuli (107–267 ms ISI) gave a similar result (n=3; 76%). Next, we asked whether sound can protect the visual stimulus from fading. From the trial's outset, one disk was paired with a coincident sound, and Ss (n=5) waited for one of the two disks to fade. On 73% of trials (60–100%), the stimulus not coincident with the sound faded first. The protection by sound was transient though: In the third experiment, the sound was turned off after 24 s, and the two stimuli alternated for 2.1 s thereafter; the stimulus paired earlier with the sound was judged more visible after the sound was turned off on 47% (6 Ss, 27–60%) of trials only. We speculate that attention to a stimulus at some location in visual space is enhanced by a sound synchronized with it. Our findings agree with past reports of audition affecting vision; we go beyond them in showing the role of synchronized sound in visual perception.