EVIDENCE FOR LIMITED-CAPACITY, PARALLEL MODELS OF VISUAL-SEARCH - A TEST OF A GENERAL GROUP-PROCESSING MODEL OF ATTENTION

Using a letter search task, we tested a new postulate of the extended feature-integration theory of attention (Treisman & Gormican, 1988), n amely the hypothesis of a continuum of attentive processing. This hypo thesis, which replaces the old dichotomy of a strict parallel vs. seri al stage, implies that groups of items can be scanned in parallel with group size depending on target discriminability. The prediction that a variation of group size leads to varying slopes of the reaction time vs. display size functions was found to be consistent with the data. More particularly, the data lend support to a general, formal group-pr ocessing model of attention, which was tested quantitatively. In addit ion, the results indicate that in visual search the relation between R T and target discriminability obeys a simple inverse power law (Jacobs , 1991 a & b).