Converging lines of evidence point to a strong link between action and perception. In this study, we show that this linkage plays a role in controlling the dynamics of binocular rivalry, in which two stimuli compete for perceptual awareness. Observers dichoptically viewed two dynamic rival stimuli while moving a computer mouse with one hand. When the motion of one rival stimulus was consistent with observers' own hand movements, dominance durations of that stimulus were extended and, remarkably, suppression durations of that stimulus were abbreviated. Additional measurements revealed that this change in rivalry dynamics was not attributable to observers' knowledge about the condition under test. Thus, self-generated actions can influence the resolution of perceptual conflict, even when the object being controlled falls outside of visual awareness.

Most research on human visual recognition focuses on solid objects, whose identity is defined primarily by shape. In daily life, however, we often encounter materials that have no specific form, including liquids whose shape changes dynamically over time. Here we show that human observers can recognize liquids and their viscosities solely from image motion information. Using a two-dimensional array of noise patches, we presented observers with motion vector fields derived from diverse computer rendered scenes of liquid flow. Our observers perceived liquid-like materials in the noise-based motion fields, and could judge the simulated viscosity with surprising accuracy, given total absence of non-motion information including form. We find that the critical feature for apparent liquid viscosity is local motion speed, whereas for the impression of liquidness, image statistics related to spatial smoothness-including the mean discrete Laplacian of motion vectors-is important. Our results show the brain exploits a wide range of motion statistics to identify non-solid materials.

After prolonged exposure to moving stimuli, illusory motion is perceived in stimuli that do not contain consistent motion, a phenomenon termed the motion aftereffect (MAE). In this study, we tested MAEs under binocular suppression that renders the motion adaptor invisible for the entire adaptation period. We developed a variant of the continuous flash suppression method to reliably suppress target motion stimuli for durations longer than several tens of seconds. Here, we ask whether motion systems are functional in the absence of perception by measuring the MAE, a question difficult to address using binocular rivalry that accompanies a switch of percept between visible and invisible. Results show that both the MAEs with static and dynamic tests are attenuated with an invisible adaptor when the adaptor and the test stimulus are presented to the same eye. In contrast, when the test pattern was presented to the other eye, the dynamic MAE was observed in invisible adaptor conditions. These results indicate that low-level adaptation survives under total binocular suppression, a finding predicted by previous studies. In contrast, disappearance of interocular transfer in the dynamic MAE suggests that a high-level motion detector does not operate when the motion adaptor is rendered invisible.

Human vision has a remarkable ability to perceive two layers at the same retinal locations, a transparent layer in front of a background surface. Critical image cues to perceptual transparency, studied extensively in the past, are changes in luminance or color that could be caused by light absorptions and reflections by the front layer, but such image changes may not be clearly visible when the front layer consists of a pure transparent material such as water. Our daily experiences with transparent materials of this kind suggest that an alternative potential cue of visual transparency is image deformations of a background pattern caused by light refraction. Although previous studies have indicated that these image deformations, at least static ones, play little role in perceptual transparency, here we show that dynamic image deformations of the background pattern, which could be produced by light refraction on a moving liquid’s surface, can produce a vivid impression of a transparent liquid layer without the aid of any other visual cues as to the presence of a transparent layer. Furthermore, a transparent liquid layer perceptually emerges even from a randomly generated dynamic image deformation as long as it is similar to real liquid deformations in its spatiotemporal frequency profile. Our findings indicate that the brain can perceptually infer the presence of “invisible” transparent liquids by analyzing the spatiotemporal structure of dynamic image deformation, for which it uses a relatively simple computation that does not require high-level knowledge about the detailed physics of liquid deformation.