Parallel and competing operations in visual and memory search

Two adjacent probe letters exposed at variable asynchrony are searched for the presence of one target letter drawn from a set of one, three, or five memorized targets. Latency of decision was longer at 70-msec ISI than at 150, 300, and 500, except that at 300-msec ISI there was also an elevated response lateney to a target when it occurred as the first of two probes. Models of search through successive probes must be qualified to accommodate these divergences from monotonicity. Interference between near-simultaneous inputs may account for the longer lateney at 70-msee ISI, and competition for processing capacity by operations at different processing stages could be involved in the effeet at 300-msec ISI. 1972, Psychonomic Society, Inc., Austin, Texas