Double dissociation of the effects of volitional control on perceptual selection and maintenance in multistable visual perception

Stimuli that give rise to multistable percepts are powerful tools for understanding the psychological and neural processes and mechanisms that create conscious perception. Research on multistable perception has resulted in substantial insights regarding the stimulus and configural factors that influence perceptual interpretations of ambiguous stimuli and the modulation of these interpretations by contextual and cognitive factors. However, relatively little is known about the effects of subjects' attempts to volitionally enhance conscious perception of one of the perceptual interpretations of a multistable stimulus. We used dichoptic presentation of Díaz-Caneja stimuli that allow four distinct perceptual interpretations: two monocular percepts (corresponding to the two monocular stimuli), and two interocularly-grouped percepts (each of which combine information from the two eyes). In different trials, participants were instructed to attempt to enhance predominance of one of the four perceptual interpretations. In contrast to the very limited effects of volitional control on conventional binocular rivalry between orthogonal gratings, we observed strong volitional enhancement of the predominance of the cued percept for Díaz-Caneja stimuli. This enhancement resulted mainly from longer mean dominance durations for the two monocular percepts and from increased probability of selection for the two interocularly-grouped percepts. A control experiment indicated that the effects of volitional control on perceptual predominance in binocular rivalry between Díaz-Caneja stimuli were unlikely to be due to response bias. These findings demonstrate distinct and dissociable processes underlying the effects of volitional control on perceptual selection and maintenance for multistable stimuli.