Abstract
When two orthogonal gratings are rapidly flickered and repetitively swapped between the eyes, observers can experience slow alternations in perceptual dominance that transcend multiple swaps. Called stimulus rivalry, this intriguing phenomenon exemplifies a form perceptual bistability that does not require eye-of-origin information and, thus, reveals visual competition between alternative image interpretations. As originally described, stimulus rivalry is experienced within a rather narrow range of stimulus conditions, and this led us to examine whether that range could be expanded. Here we report a novel condition that promotes the incidence of stimulus rivalry. In the original stimulus rivalry paradigm, dissimilar patterns are rapidly and repetitively turned “on” and “off” while being exchanged between the eyes. In our first experiment, we replaced the “off” periods with dioptic presentation of a composite of the two rival targets, reasoning that this composite would reduce the impact of visual transients by establishing continuous stimulation in both eyes. Indeed, stimulus rivalry occurred over a wider range of spatial and temporal frequencies. A second experiment examined why the composite might work by measuring the incidence of stimulus rivalry for brief rival presentations immediately following prolonged adaptation to a static composite, a flickering composite or a gray background. Observers experienced stimulus rivalry significantly more often following both static and flickering adaptation, compared to the gray background. These findings expand the range of conditions yielding stimulus rivalry and offer suggestive reasons why stimulus rivalry circumvents interocular competition in the first place.