Flash Suppression: Competition Between Eyes or Patterns?

Gabriel Kreiman, Christof Koch

Association for Research in Vision and Opthalmology, Fort Lauderdale, 1998

Purpose: Flash suppression consists of the perceptual suppression of one stimulus that was previsly presented monocularly to one eye upon flashing a new stimulus to the other eye. Does this represent a competition between the two eyes or between the two alternative patterns? Methods: A stimulus is monocularly presented for 1-2 seconds. After an inter0stimulus interval (varies between 0 and 100 ms) a second stimulus is flashed (20-200 msec) to the same eye while the original image is simultaneously presented to the other eye (swapped flash suppression). Subjects respond in a 3 alternative forced choice task indicating whether they perceived one of the stimuli exclusively or a mixture of them (as in piecemeal rivalry). We used sinusoidal gratings of different orientations as well as more complex stimuli such as faces, objects and geometric patterns. Results: Subjects do not report perceiving the original stimulus either in the classic or in the swapped flash suppression experiment. The new pattern dominates perception in both classic and swapped conditions but there is also a significant proportion of cases where subjects report perceiving a mixture under the swapped flash suppression test. Conclusions: We find that the pattern is more important than the eye in predicting perception. This is consistent with some similar results that have been obtained under binocular rivalry. An exclusive inhibition of one eye cannot account for flash suppression.