Dissociations in memory for item identity and item frequency: evidence from hemispheric interactions.

Evidence for a dissociation between memory for the identity of an item and memory for its frequency of occurrence was provided by two tachistoscopic studies employing lateralized abstract designs as stimuli. In both experiments, subjects viewed a random series of presentation trials, in which certain designs appeared only once, others 5 times, and still others 9 times. Then in a series of probe trials, subjects decided, on each trial, if a design was familiar or novel, either by an old/new decision (Experiment 1) or a forced-choice decision (Experiment 2), after which they estimated the frequency of item occurrence. Presentation and probe trials were either displayed in the same visual field (within-hemisphere trials) or opposite visual fields (across-hemisphere trials). Both experiments revealed that the pattern of interhemispheric processing as well as lateralized processing differed for item identity as compared to item frequency, providing further evidence for a dissociation between these two memory processes.