Search asymmetry in periodical changes of motion directions

Abstract

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.