In a series of psychophysical experiments, observers discriminated between briefly flashed stimuli (cosine gratings, cosine plaids) that were either identical to the two eyes (dioptic) or differed between the two eyes (dichoptic). Although dioptic and dichoptic binocular stimuli were perceptually similar, they were distinguishable well above chance at exposure durations too brief for the onset of binocular rivalry. Random variations in display contrast did not alter this pattern of results. These results show that the neural events that signal false fusion of dissimilar monocular stimuli are not equivalent to those that underlie binocular fusion of matched monocular views.