Introspective forgetting

We model the forgetting of propositional variables in a modal logical context where agents become ignorant and are aware of each others’ or their own resulting ignorance. The resulting logic is sound and complete. It can be compared to variable-forgetting as abstraction from information, wherein agents become unaware of certain variables: by employing elementary results for bisimulation, it follows that beliefs not involving the forgotten atom(s) remain true. The work for this publication was mainly carried out while Hans van Ditmarsch was associated to: Institut de Recherche en Informatique, Université Paul Sabatier, France.     

Very rapid forgetting

Human forgetting can be much more rapid than previous experiments have indicated. Subjects who do not expect a test after a filled retention interval can rarely recall three consonants correctly after 2 sec of distraction. If there are two kinds of memory, primary and secondary, the present technique provides a purer method of studying forgetting from primary memory.     

When remembering causes forgetting: retrieval-induced forgetting as recovery failure

Retrieval practice on a subset of previously learned material can cause forgetting of the unpracticed material and make it inaccessible to consciousness. Such inaccessibility may arise because the material is no longer sampled from the set of to-be-recalled items, or, though sampled, its representation is not complete enough to be recovered into consciousness. In 2 experiments, it was examined whether retrieval-induced forgetting reflects a sampling or recovery failure by studying the time course of cued recall in this type of situation. Although retrieval practice reduced recall totals of the unpracticed items, in both experiments, the forgetting was not accompanied by an effect on the items' response latencies. This pattern of results is consistent with the view that inhibited items are successfully sampled but, because of a reduction in their activation level, do not exceed the recovery threshold.     

Interference resolution in retrieval-induced forgetting: Behavioral evidence for a nonmonotonic relationship between interference and forgetting

Retrieving memories renders related memories less accessible. This phenomenon, termed retrieval-induced forgetting (RIF), is thought to be the result of processes that resolve interference during competitive retrieval. In several studies, researchers have manipulated the level of interference to test different theoretical accounts of RIF (e.g., inhibitory vs. noninhibitory). However, the nature of how interference and RIF are related has not been systematically investigated. Here, we introduce a design that allows for assessing interference during competitive retrieval by measuring the recall RTs associated with target recall. Using such a design, we found that RIF occurred only when interference during competitive retrieval reached moderate levels, but not when it was too low or too high. This finding might indicate that low levels of interference do not trigger interference resolution, whereas interference resolution might fail when the interference reaches extremely high levels.     

Divided attention facilitates intentional forgetting: evidence from item-method directed forgetting

This study examined the effects of post-cue interval and cognitive load on item-method directed forgetting. The results of Experiment 1 (free recall test) and Experiment 2 (cued recall test) showed that forget item retention increased as the post-cue interval increased. Moreover, increasing the cognitive load of participants by asking them to perform a secondary counting task did not impair, but rather facilitated, the intentional forgetting of the studied item under long post-cue interval conditions. These results and analyses of recall gains from the additional use of the independent cue suggest that the improved recall of forget items caused by an increase in the post-cue interval came from an automatic process, and that after receiving the forget cue, participants did not engage a suppression operation that was resource-demanded. The current findings suggest that forgetting is more effective when participants perform a secondary task after receiving the forget cue.     

Retrieval-induced forgetting: Evidence for a recall-specific mechanism

Previous work has shown that recalling information from long-term memory can impair the long-term retention of related representations—a phenomenon known as retrieval-induced forgetting (Anderson, Bjork, & Bjork, 1994). We report an experiment in which the question of whether retrieval is necessary to induce this form of impairment was examined. All the subjects studied six members from each of eight taxonomic categories (e.g.,fruit orange). In the competitive practice condition, the subjects practiced recalling three of the six members, using category-stem cues (e.g.,fruit or____). In the noncompetitive practice condition, the subjects were reexposed to these same members for the same number of repetitions but were asked to recall the category name by using the exemplar and a stem as cues (e.g.,fr____orange). Despite significant and comparable facilitation of practiced items in both conditions, only the competitive practice subjects were impaired in their ability to recall the nonpracticed members on a delayed cued-recall test. These findings argue that retrieval-induced forgetting is not caused by increased competition arising from the strengthening of practiced items, but by inhibitory processes specific to the situation of recall.     

Varieties of graded forgetting

Forgetting is typically viewed as counterproductive in everyday life. However, it may mainly be harmful when it is complete, that is, all-encompassing and permanent, and not when it is graded, that is, partial and fluctuating. I propose that forgetting is in fact mostly graded, and that this is an essential reason that it is often helpful. I delineate three ways in which forgetting may be graded. First, it may occur with respect to one, but not another, part of a memory. Second, it may occur in one context, but not in another. Third, forgetting may be present at one point in time, but not at another. Also, I propose that different levels of forgetting are possible, based on whether an engram or a context is unavailable, silent, restricted, latent, or potent. Overall, I hypothesize that forgetting is often helpful because it can be flexible and tailored to the circumstances.     

Episodic generation can cause semantic forgetting: Retrieval-induced forgetting of false memories

In two experiments, we tested whether false recognition and false recall were prone to retrieval-induced forgetting, using the retrieval practice paradigm (Anderson, Bjork, & Bjork, 1994). Participants encoded lists of cue-target word pairs associated with a nonpresented, critical theme word and then engaged in retrieval practice for half of the word pairs from half of the lists. As expected, unpracticed targets from practiced lists were recognized (Experiment 1) and recalled (Experiment 2) less well than those from unpracticed lists. In addition, false recognition and false recall of critical items associated with practiced lists was lower than false recognition and false recall of items associated with unpracticed lists. We argue that false memories are prone to inhibitory mechanisms engendered by the retrieval practice paradigm. The results are consistent with the claim that semantically activated critical themes interfere with the episodic retrieval of list words and that inhibition decreases the activation level of these interfering memory representations during retrieval practice.     

The crucial role of postcue encoding in directed forgetting and context-dependent forgetting

People can intentionally forget previously studied material if, after study, a forget cue is provided and new material is learned. It has recently been suggested that such list-method directed forgetting arises because the forget cue induces a change in internal context and causes context-dependent forgetting of the studied material (L. Sahakyan & C. M. Kelley, 2002). The authors compared directed forgetting and context-dependent forgetting by examining whether, like a forget cue, a change in internal context needs subsequent learning of new material to be effective. Participants studied an item list and, after study, received a remember cue or a forget cue or their internal context was changed through an imagination task. In each condition, half the participants learned a second list, and the other half fulfilled an unrelated distractor task. Both the forget cue and the change in internal context induced forgetting of the first list only when learning of the second list was interpolated. These results suggest that postcue encoding of new material is crucial for both directed forgetting and (some forms of) context-dependent forgetting.     

The benefit of forgetting

Recent research using change-detection tasks has shown that a directed-forgetting cue, indicating that a subset of the information stored in memory can be forgotten, significantly benefits the other information stored in visual working memory. How do these directed-forgetting cues aid the memory representations that are retained? We addressed this question in the present study by using a recall paradigm to measure the nature of the retained memory representations. Our results demonstrated that a directed-forgetting cue leads to higher-fidelity representations of the remaining items and a lower probability of dropping these representations from memory. Next, we showed that this is made possible by the to-be-forgotten item being expelled from visual working memory following the cue, allowing maintenance mechanisms to be focused on only the items that remain in visual working memory. Thus, the present findings show that cues to forget benefit the remaining information in visual working memory by fundamentally improving their quality relative to conditions in which just as many items are encoded but no cue is provided.     

Short-term forgetting without interference

In the 1st reported experiment, we demonstrate that auditory memory is robust over extended retention intervals (RIs) when listeners compare the timbre of complex tones, even when active or verbal rehearsal is difficult or impossible. Thus, our tones have an abstract timbre that resists verbal labeling, they differ across trials so that no "standard" comparison stimulus is built up, and the spectral change to be discriminated is very slight and therefore does not shift stimuli across verbal categories. Nonetheless, performance in this nonverbal immediate memory task was better at short (1-, 2-, or 4-s) than long (8-, 16-, or 32-s) RIs, an outcome predicted by temporal distinctiveness theory whereby at long RIs, tones are closer in time to tones on previous trials. We reject this account in the 2nd experiment, where we demonstrate that the ratio of RI to intertrial interval makes absolutely no difference to performance. We suggest that steady forgetting is consistent with a psychoacoustically derived conception of an auditory memory (the timbre memory model) that embodies time-based forgetting in the absence of feature-specific interference.     

Cue discrimination and forgetting

Subjects learned paired associate fists in which word triads were paired with nouns to a partial criterion; they were then given both an immediate and a 1-week delayed recognition test for discrimination among the triads and a cued recall test. Recall after 1 week was slightly poorer than that occurring immediately, but it was unaffected by various patterns of element identity among the triads. Discrimination improved somewhat over the 1-week interval. Further experiments showed that the immediate test was responsible for both reducing forgetting and improving discrimination, but both effects were independent of identity structure. Forgetting cannot be attributed to loss of differentiation of cues.     

Retrieval-induced forgetting in rats

“Retrieval-induced forgetting” in rats was evaluated using a modified spontaneous object recognition test. The test consisted of a sample phase, retrieval or interference phase, and a test phase with 60-min delay period inserted between the phases. Rats were randomly assigned to one of three groups (control, retrieval and interference) and allowed to explore the field in which two different objects (A, B) were placed in the sample phase. In the retrieval phase, two identical objects (B, B), which were the same as one of the objects presented in the sample phase, were placed again. In the interference phase, two identical objects (C, C), which were novel for animals, were placed. In the test phase, two different objects (A, D), one of which was identical to that presented in sample phase (familiar object) and the other was novel, were placed and the time spent exploring each object was analyzed. While the exploration of the novel object was significantly longer than that of the familiar object in rats subjected to the interference phase, rats subjected to the retrieval phase could not discriminate between the familiar and the novel objects at the test phase. These results demonstrate the “retrieval-induced forgetting” phenomenon in a spontaneous object recognition test in rats.     

Depressive deficits in forgetting

The aim of this study was to investigate whether difficulties in forgetting (like difficulties in remembering) are associated with depressive states. First, dysphoric and nondysphoric students learned 40 word pairs, each consisting of a positive or negative adjective and a neutral noun (target). Next, the students practiced responding with some targets and suppressing others, when given the adjective as cue, for a varied number of repetitions. On the final test, they were told to disregard the prior instruction to suppress and to recall the target associated with every cue. Compared with nondysphoric students, dysphoric students recalled similar percentages of targets from sets assigned for response practice but higher percentages from sets assigned for suppression practice. The degree of forgetting showed some mood-congruent tendencies and was significantly correlated with self-report measures of rumination and unwanted thoughts.     

Reducing interference in forgetting

According to interference theories forgetting results from the intervention of extraneous associations which disturb the patterns built up during learning. It also seems that the period immediately following learning is critical for forgetting. The experiment which is described was carried out to investigate whether administration of the central-depressant drug nitrous oxide immediately after learning would reduce forgetting, since it had been shown to impair the formation of associations and ought therefore to reduce interference. This expectation was borne out, significantly less forgetting occurring when nitrous oxide was given than when air was given. A possible physiological basis, relating these results to those for sleep is discussed.