Daniel Kahneman Avishai Henik
The Hebrew University of Jerusalem Jerusalem, Israel
A phenomenon labeled "group processing" is observed when arrays of letters or digits organized in perceptual groups are presented for immediate recall. Recall probabilities are similar within each group and vary sharply between groups. Grouped items tend to be recalled in all-or-none fashion, but there is evidence of competition between groups in recall. Adding an item to the last group in the array depresses performance in that group. The interference is equally severe when the added item is a relevant digit or an irrelevant suffix. These effects are predicted by a model of allocation rules for attention or processing resources. Alternative interpretations, in terms of visual interference or hierarchical coding, are tested and rejected. Grouping structure has very strong effects in a task of selective attention by color: total performance depends on the complexity of grouping, and the groups that occur late in the processing queue are affected most severely by the presence of irrelevant material.
In this chapter we are concerned with several aspects of a single question: How does perceptual grouping affect the recall of tachistoscopically exposed arrays of digits or letters? We report experiments in which subjects are shown arrays of unrelated items, variously organized in groups by manipulations of similarity or proximity. In some experimental conditions, all the material that is presented is