Simultaneous visual events show a long-range spatial interaction

A stimulus consisting of two brief flashes separated by a short interval appears to flicker, whereas a single brief flash does not. Performance on a task requiring discrimination of double and single stimuli is adversely affected by simultaneous presentation of a second, similar stimulus at a relatively remote position in the visual field. Most errors occur when target and mask follow different time courses, one double and the other single. The results of four experiments studying this interaction are reported. An effect on performance is observed under binocular, monocular, and dichoptic viewing conditions. Performance is affected up to target to mask distances of at least 20 deg of arc. Performance increases as target-to-mask onset asynchrony is increased, reaching asymptote at asynchronies of between 100 and 150 msec. The precise shape of the stimuli does not appear to be important in determining the size of the effect or whether or not an effect occurs. An analogy between this effect and apparent movement is suggested.