Bistable stroboscopic motion percepts can be generated when two frames, each consisting of three square elements, are presented alternately at varying interstimulus intervals (ISIs). Endto-end element motion is observed at short ISIs; group motion is observed at long ISIs. We found that the ISIs at which transitions from element to group motion occurred decreased as (1) viewing eccentricity, (2) element size, and (3) frame durations increased. Since visual pattern persistence also decreases as each of these three parameters increases, we conclude that such persistence plays a role in determining which percept dominates in bistable stroboscopic motion.One phenomenon that accompanies a briefly displayed stimulus pattern is visual pattern persistence. Two such patterns displayed in spatiotemporal sequence additionally produce the sensation of stroboscopic motion. Since pattern persistence also occurs in two-or multiple-pattern sequences (Allport, 1968;Di Lollo & Hogben, 1985), we can ask how and to what extent persistence and stroboscopic motion are related (e.g., see Farrell, 1984). To address this question, we investigated the competing bistable stroboscopic motion percepts reported by Pantle and Picciano (1976). To produce such percepts, stimuli such as those shown in Figure 1 are presented in cyclic alternation. Frame 1 contains three equispaced and horizontally arrayed elements; Frame 2 contains the same elements displaced to the right by the center-to-center distance separating two adjacent elements. Thus, the two right elements of Frame 1 and the two left elements of Frame 2 overlap spatially. When these two frames are alternately flashed for several cycles at varying interstimuIus intervals (ISIs), one can observe one of two motion percepts, depending on lSI. At short ISIs, one sees the middle two, overlapping elements as stationary and the endmost elements moving back and forth. This perception of end-to-end element motion is replaced at longer ISIs by a perception of group motion in which three elements are seen to move back and forth as a group.In a separate study (Breitmeyer & Ritter, in press), we showed that an overall increase of group motion-and hence a decrease of element motion-could be effected by increasing either element size or, as Petersik and Pantle (1979) had done, frame duration. In particular, the lSI at which transitions from element to group motion occurred decreased with increases in element size or frame durations. These results were interpreted in terms of the Requests for reprints should be directed to B. G. Breitmeyer, Department of Psychology, University of Houston, University Park, Houston, TX 77004. hypothesis that the perception of end-to-end element motion depends on the perception of stationarity of the inner two elements (Braddick, 1980; Braddick & Adlard, 1978;Pantle & Petersik, 1980). That is to say, over successive frames, the spatially overlapping elements are temporally integrated by the perceptual system. Moreover, we suggested that a process responsible for such ...
