M. S. Weldon and K. D. Bellinger (1997) showed that people who collaborate on a recall test (collaborative group) perform much more poorly than the same number of people tested individually (nominal group). Four experiments tested the hypothesis that retrieval-strategy disruption underlies this collaborative inhibition when categorized lists are studied. Collaborative groups performed worse than nominal groups when categories were large (Experiment 1) and when category names were provided at recall (Experiment 2). However, collaborative- and nominal-group recall were equivalent when participants retrieved nonoverlapping parts of the list (Experiment 3) and when participants were forced to organize their recall by category (Experiment 4). Clearly, disorganized retrieval can account for collaborative inhibition with the materials and procedures used here.

Directed forgetting has been studied by instructing Ss to forget either (a) an initial list or (b) individually selected words. Differential encoding was hypothesized to be responsible for wordmethod directed forgetting, and retrieval inhibition for list-method directed forgetting. In Experiments 1 and 2, directed forgetting was observed in recognition with the word method but not with the list method. Release from directed forgetting occurred in final recall after recognition but only with the list method. These results are interpreted in terms of a theoretical framework that integrates distinctive-relational processing theory with revised generation-recognition theory. In Experiments 1-3, predictions from that framework were generally well supported on implicit and explicit retention tests that provided the same stimulus conditions. Consistent with processing theory, list-method directed forgetting was absent on data-driven or conceptually driven implicit tests, and word-method directed forgetting was absent on data-driven implicit tests.

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Collaborative inhibition, the poorer memory performance of collaborative groups as compared with nominal (noninteracting) groups was measured in the free recall of categorized lists. In Experiment 1, collaborative inhibition was present in four-person groups, but not in pairs of two-person groups, where each was compared with performance in four-person nominal groups. However, on a ®nal individual free recall test, members of two-and fourperson collaborative groups recalled a higher proportion of the list than members of nominal groups. In Experiment 2, recall in three-person collaborative groups was less than in threeperson nominal groups but only on the ®rst of three successive study-test trials. On the ®nal individual free recall test, members of collaborative groups recalled more words than members of nominal groups. Despite inhibiting recall and reminiscence, collaboration bene®ts remembering when collaborators are subsequently tested individually.Collaborative remembering refers to the eorts of two or more individuals working together to produce a common record of their recollections. Although active interest in the memorial consequences of collaboration is fairly recent (e.g. Weldon and Bellinger, 1997;Basden et al., 1997), social psychologists have long been interested in the de®cits associated with collaboration. Their research has focused on the eect of brainstorming on problem solving. The in¯uence of collaboration is determined by comparing the performance of collaborative groups with that of nominal groups. Performance of nominal groups is determined by pooling the output of the same number of people working individually at the same task. In general, nominal groups provide a greater number of unique problem solutions than do collaborative groups (see Clark and Stephenson, 1989, for a review).In like fashion, recent studies of collaborative memory have compared the performance of nominal and collaborative groups. Weldon and Bellinger (1997) found non-redundant recall (the memory equivalent of unique ideas) to be greater for nominal than for collaborative groups and to be greater for collaborative groups than for individuals. The latter result had been expected from prior research on group remembering (e.g. Vollrath et al., 1989). Weldon and Bellinger referred to lower collaborative than nominal group recall as collaborative inhibition.

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