The processing of hierarchical stimuli: Effects of retinal locus, locational uncertainty, and stimulus identity

Abstract

Three experiments examined the effects of changes in retinal locus and locational uncertainty in the processing of hierarchical stimuli. In Experiment 1, stimuli were presented randomly in the left, center, or right portions of a display. Central presentation decreased reaction times for identifying small letters presented within a hierarchical stimulus pattern (i.e., local letters) but not for a single small letter presented alone. In Experiment 2, all stimuli were presented centrally, thus eliminating the locational uncertainty that existed in Experiment 1. The elimination of locational uncertainty resulted in faster reaction times (as compared with the central data of Experiment 1) for identifying small letters, whether or not they appeared in a hierarchical pattern. In Experiment 3, eye movements were monitored and eliminated as a possible source of these effects. The results are discussed in terms of possible effects of an attentional "spotlight" on hierarchical stimulus processing. It was also found that the identity of the target letter (i.e., whether it was an H or an S) had a large effect on performance. Finally, in contrast to earlier findings (Hoffman, 1980; Martin, 1979), the response-time advantage at a given level and the amount of Stroop-type interference produced at the other level did not always covary, suggesting that these two effects may reflect the operation of separate mechanisms. © 1988 Psychonomic Society, Inc.