Effects of scopolamine on verbal memory; a retrieval or acquisition deficit?

This study examines the relationship between encoding and retrieval factors in producing the well-documented scopolamine-induced deficits in verbal memory. Subjects were required to learn word lists of 10 items, and were given a total of 8 acquisition trials per list. While the placebo group achieved criterion within 4 acquisition trials, the group treated with scopolamine failed to reach criterion at all, with recall levelling off within 4 acquisition trials. Acquisition curves for subjects treated with scopolamine paralleled those obtained for the placebo group. Performance on delayed recall and recognition tests indicated that the subjects had in fact successfully encoded items in long-term memory, but had been unable to retrieve them in free recall. The results suggest a retrieval problem in what has traditionally been considered a scopolamine-induced encoding deficit. We suggest that scopolamine may disrupt the organization of material at input, so that items which have achieved durable storage are not accessible for free recall.