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Article Excerpt
Forgetting usually occurs imperceptibly and spontaneously with the passing of time and is often considered a major memory problem. In some circumstances, however, forgetting is exactly what we need to do to function efficiently (see Anderson & Schooler, 2000 for an adaptive analysis of forgetting). First, a key to accurate memorization is the ignoring or inhibition of irrelevant information. For orderly and purposeful memory function, information must be classified as relevant or irrelevant, memory must be constantly updated, and only those memories relevant to the task at hand should be retrieved. Second, people often try to forget unwanted memories, such as events in their lives that are painful or embarrassing.
The issues related to intentional forgetting and suppression have involved many areas in psychology, such as social, clinical and cognitive psychology. Nonetheless, so far, the mechanisms of forgetting/suppression remain poorly understood. Different areas of study often produced mixed results. Studies on directed forgetting, conducted mostly by cognitive psychologists, have shown that forgetting can be intentional and controllable (see MacLeod, 1998, for a review). On the other hand, studies on thought suppression, the concern of clinical and social psychologists, tend to suggest that people have difficulties in suppressing unwanted thoughts (see Wegner, 1994; Wenzlaff & Wegner, 2000, for reviews). Yet the notion of repressing unwanted memories is central to psychoanalytic theory. However, studies on repression sometimes support the idea that unwanted memories can be repressed and then recovered, and sometimes not (see Loftus & Ketcham, 1994). The purpose of this study was to find a possible factor that was related to both intentional forgetting and thought suppression by examining the effect of post-cue interval.
Substantial literature has been devoted to directed forgetting (see Johnson, 1994; MacLeod, 1998, for reviews). Two common procedures have been used in directed forgetting research to present instructional cues to participants regarding items they should forget or remember. Under the item method, participants are given explicit cues for each to-be-forgotten item (F item), such as 'forget', and for each to-be-remembered item (R item), such as 'remember'. The memory cue comes after the relevant item to ensure that the participant has registered the words. The list method only involves one cue, usually an instruction to forget all the preceding items, given in the middle of the list. The directed forgetting effect describes the finding that F items are less well remembered than R items, and sometimes proactive interference on the R items followed by the F items is reduced.
The occurrence of this effect depends on how memory is tested. When participants are tested with a recall test, both item and list method produce a directed forgetting effect. However, when participants are tested using a recognition test, rather than a recall test, only the item method produced such an effect (e.g. Block, 1971; MacLeod, 1975). Based on this and other findings, several studies have suggested that the item method fosters selective rehearsal favouring the R items, whereas the list method promotes inhibition of the F items (Basden & Basden, 1998; Basden, Basden, & Gargano, 1993; MacLeod, 1999; Wilson & Kipp, 1998). In the item method, the F items are less well rehearsed than the R items and thus F items are not encoded as completely as R items. This phenomenon impairs both recognition and recall for F items. In the list method, both R items and F items are encoded and stored in memory. The cue to forget affects retrieval access to F items. Consequently, the directed forgetting effect was found only in the recall test and not in the recognition and indirect memory tests, in which active retrieval is not necessary (e.g. Basden et al., 1993).
Some studies using the item method have found results consistent with the retrieval inhibition account, however. Firstly, Weiner and Reed (1969) found higher recall in the unrehearsed remember condition than in the active forgetting condition, suggesting that the active forgetting was not a result of mere nonrehearsal. Roediger and Crowder (1972), nonetheless, found evidence suggesting that the forgetting effect was due to covert rehearsal in the nonrehearsal remember condition. Secondly, Geiselman and Bagheri (1985) found greater memory gains for the initial F items than the R items and proposed that this was evidence for the releasing of F items from retrieval inhibition. Findings from directed forgetting on indirect memory tests are also consistent with the notion of retrieval inhibition (MacLeod, 1989). On the other hand, Basden et al. (1993) suggest that MacLeod's result may have been contaminated by explicit retrieval and the evidence from Geiselman and Bagheri was not compelling; thus the role of retrieval inhibition in the item method of forgetting is negligible.
If directed forgetting is mediated by processes that enhance the rehearsal of remember items rather than by processes that suppress or inhibit the retrieval of forget items, then F items ought to be ignored after the forgetting cue. As a result, increasing the post-cue interval should improve memory only for R items and not for F items. Specifically, memory for R items should increase as a function of the immediate rehearsal period, whereas the retention for F items ought to remain stable over such a period. Although many studies have investigated the effect of pre-cue interval on directed forgetting (e.g. Timmins, 1974; Woodward, Bjork, & Jongeward, 1973), we found only one study in the literature testing this prediction. Allen and Vokey (1998) manipulated the time available to retrieve and rehearse an item following an instruction to remember or forget it. They found that the directed forgetting effect did not vary as a function of the time available (1 vs. 3 seconds) for rehearsal and occurred even for items immediately followed by a remember item (zero lag). Thus, they concluded that some process at the time of the first instruction to remember or to forget was responsible for the directed forgetting effect and that additional rehearsal opportunities played no significant role in directed forgetting.
There were several problems with this study, however. Firstly, the difference between the post-cue intervals of 1 vs. 3 seconds might not be large enough to create a difference in the directed forgetting effect. This was very likely because the investigators also did not find an expected effect of rehearsal (post-cue interval) on R items (compare with Wetzel & Hunt, 1977). Secondly, even at the shortest rehearsal times (1 second), on the average R items still had more chances to be rehearsed than the F items because participants are very likely to take every instruction to forget as a period in which to retrieve and to rehearse prior R items. Thus, the single-retrieval hypothesis proposed by Allen and Vokey (1998) was not the only explanation.
Thirdly, their manipulation of training lag (the number of F items given prior to an R item) might not be effective, because the post-cue interval for F...
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