POSITIONAL DISTINCTIVENESS AND THE RATIO RULE IN FREE-RECALL

The ratio rule relates the recency effect in free recall to the ratio of the duration of the interitem presentation interval (IPI) and the r etention interval (RI). Three experiments examined this ratio rule in an immediate memory setting. An approximately linear relationship was discovered to hold over ratios ranging from 1:12 to 12:1 (Experiment 1 ), and also for constant ratios ranging from 1:1 to 12:12 (Experiments 2 and 3). However, in contrast to a ''true'' ratio rule, recency syst ematically decreased with increases in absolute duration, despite a co nstant IPI to RI ratio. A new distinctiveness model is proposed that a ccurately predicts the reported empirical relationships. The model inc orporates a precise definition of stimulus distinctiveness, based on t he dimensional distinctiveness model, and includes a specific mechanis m to account for how the distinctiveness of each item arises, based on the perturbation model. (C) 1997 Academic Press.