Effect of retention interval on implicit and explicit memory for pictures

Abstract

A picture-fragment completion task and a yes-no recognition task were used to determine whether rates of forgetting in perceptual (implicit) and episodic (explicit) memory systems were the same. In Session 1, identification thresholds for 60 fragmented pictures were measured. In Session 2, which occurred after one of four delay periods (immediate, 2 days, 7 days, or 14 days), the subjects were presented with half of the pictures shown in the previous session mixed with an equal number of new pictures, and their identification thresholds were measured. A yes-no recognition test for the picture names (90 names of pictures shown in the picture-fragment completion task, 30 new-picture names) was given after the identification phase, and both speed and accuracy of recognition were measured. Perceptual learning was measured by relative savings in identification of repeated, compared to new, pictures. Episodic learning was measured in two ways: by the corrected recognition score for names of pictures presented in Session 1 alone (hits minus false alarms) and by the difference in hit reaction times between Session 1 pictures and the new pictures presented for identification in Session 2. These three learning measures showed approximately equal rates of forgetting; furthermore, the episodic learning measure based on accuracy showed more similarity to the perceptual learning measure than it did to the episodic learning measure based on reaction time. Accordingly, the results of this experiment do not support functional dissociation of implicit and explicit memory systems by different forgetting rates.