Parallel perceptual processing and decisional strategies: A reinterpretation of the Shaw and LaBerge effect

A reinterpretation is offered for an effect found by Shaw and LaBerge (1971) in a tachistoscopic detection paradigm. Their Ss were instructed to “scan” the letters of a multiletter stimulus array in a particular sequence. The Ss were more accurate in identifying a target letter if it occurred earlier rather than later in the instructed sequence. Although Shaw and LaBerge interpreted this result as supporting a limited-capacity attentional mechanism, the result is also consistent with a nonattentional parallel processing conception: the payoff incentives used to encourage the correct “scanning sequence” could alter Ss’ postperceptual decisional strategy so as to produce the results obtained. Given the compatibility of a parallel processing conception with the results of Shaw and LaBerge and the results of other detection experiments, the need for postulating a spatial capacity limit or attentional mechanism is questioned.