Local motion signals silence the perceptual solution of global apparent motion.

Stimuli for apparent motion can have ambiguity in frame-to-frame correspondences among visual elements. This occurs when visual inputs cause a correspondence problem that allows multiple alternatives of perceptual solutions. Herein we examined the influence of local visual motions on a perceptual solution under such a multistable situation. We repeatedly alternated two frames of stimuli in a circular configuration in which discrete elements in two different colors alternated in space and switched their colors frame by frame. These stimuli were compatible with three perceptual solutions: globally consistent clockwise and counterclockwise rotations and color flickers at the same locations without such global apparent motion. We added a sinusoidal grating continuously drifting within each element to examine whether the perceptual solution for the global apparent motion was affected by the local continuous motions. We found that the local motions suppressed global apparent motion and promoted another perceptual solution that the local elements were only flickering between the two colors and drifting within static windows. It was concluded that local continuous motions as counterevidence against global apparent motion contributed to individuating visual objects and integrating visual features for maintaining object identity at the same location.

Search asymmetry in periodical changes of motion directions.

We often need to search for an object in a dynamic environment. However, there remains a limited understanding of search processes responding to dynamic inputs of stimuli, especially regarding the mid-level stages of our visual processing hierarchy. In this study, we investigated whether and to what extent search asymmetry is observed between a search for a directionally changing item among constantly drifting items and vice versa. We found a significant search asymmetry in which a search for a directionally changing target among constantly drifting distractors was fairly efficient, while a search for a constantly drifting target among directionally changing distractors was drastically inefficient. We compared these results with other cases of search for a color-changing item among color-constant items and vice versa. These results suggest that directional changes are not a guiding attribute, but they are processed differently depending on whether they are assigned as a target to be found or distractors to be rejected; in the latter case, observers have difficulty rejecting them as distractors. We propose that the significant search asymmetry reflects the period of time during which directional changes are temporarily inaccessible to the visual system when deciding between a distractor and a target.