Global and local precedence: Selective attention in form and motion perception

Five experiments traced the causes of the discrepancy in research that showed both local and global precedence in selective attention tasks. The effects of the relative discriminabilities of the local and global levels of the stimuli and the differences between Stroop-type interference (attributable to incongruity on the irrelevant dimension) and Garner-type interference (attributable to variability on the irrelevant dimension) were explored. The experiments also examined whether the precedence effects previously examined in form perception generalize to motion perception. 45 Ss, most of whom were college students, participated. Ss viewed stimuli on an oscilloscope under 9 conditions. Results show that (a) some cases of global precedence were due solely to the greater perceptual discriminability of the global level; (b) instances of both local and global precedence could be demonstrated for certain types of stimuli, even when the discriminabilities of their local and global levels had been equated; and (c) the Stroop and Garner measures of selective attention were not equivalent but instead measured different types of interference. It is concluded that cases of both local and global precedence have been amply documented but that no general theory can account for why or when these effects will appear until a better understanding is gained of both the nature of part-whole relationships and the perceptual processes that are tapped by different measures of selective attention. (31 ref)