Locus of the effect of a distinguishing feature in a memory search task

Subjects memorized one to four 8- or 16-sided random forms in a memory search task. The positive set forms ("yes" response) differed in number of sides from the negative set forms ("no" response) for the different set (DS) group, but this distinguishing feature was not available to the same set (SS) group. Mean reaction time increased as a linear function of log(2) of the positive set size for both groups, but the increase was greater for the SS than the DS group, suggesting that memory search rather than an encoding stage of information processing was influenced by the availability of a distinguishing feature. In a transfer task which followed, new forms were introduced in which the positive and negative set forms differed in number of sides for both groups. In this task, the two groups did not differ in memory search, but in encoding. It was proposed that (a) availability of a distinguishing feature influences search time because the information specifying the number of sides of the set of memorized forms can be used to influence the speed with which individual forms are examined in memory; (b) previous experience with a distinguishing feature influences encoding because the DS group had learned to extract the information specifying the set of memorized forms (not the information specifying individual forms) more efficiently than the SS group.