Time-Shared Visual Awareness of Multiple Moving Objects
43.4064, Monday, 18-May, 8:30 am - 12:30 pm, Pavilion
Joseph Lappin1, Douglas Morse2, Adriane Seiffert1; 1Psychology, Arts & Science, Vanderbilt University, 2Psychology & Human Development, Peabody College, Vanderbilt University
How does vision encompass multiple moving objects? Well-trained observers monitored ongoing patterns of randomly moving objects, trying to quickly detect a non-random target motion (pursuit of a visible ‘prey’) by any one of the objects. Three experiments evaluated effects of the set size of observed objects (n = 1 – 12) on the temporal process of motion detection. Strikingly lawful effects on motion detection were observed: (1) Detection rates slowed in direct proportion to set size. (2) Two simultaneous visual processes governed motion detection — spatiotemporal motion integration (independent of conscious awareness), and constant-rate transfer into conscious awareness. The rates of both reflected time-shared parallel processes divided among the set of moving objects. Conventional RT analyses inadequately described the temporal process. Conditional detection rates for targets not yet detected — hazard rates (bits/sec), rates of change in RT — revealed simple lawful effects of set size on motion detection. For all observers, set sizes, motion speeds, and response times, detection rates had two phases: a first phase (~ 0.4 s) of motion integration in which detection rates increased linearly with time, followed by a second phase of constant-rate detection invariant with increasing time and motion. Detection rates decreased proportionally with set size in both phases. In Exp. 1, (n = 2, 4, 6, 8 objects), this two-phase process (3 parameters) described 98% of the variance of detection rates associated with set size and response time (Fig. 1). Exp. 2 (n = 1, 4, 12) found that greater motion speed yielded faster detections, but detection rate in spacetime was invariant with motion speed. Exp. 3 (n = 1, 2, 4, 8) found that early motion integration was hindered without a visible ‘prey’ object, but later awareness of the motion was unaffected.