How does acoustic similarity influence short-term memory?

This study attempts to discover why items which are similar in sound are hard to recall in a short-term memory situation. The input, storage, and retrieval stages of the memory system are examined separately. Experiments I, II and III use a modification of the Peterson and Peterson technique to plot short-term forgetting curves for sequences of acoustically similar and control words. If acoustically similar sequences are stored less efficiently, they should be forgotten more rapidly. All three experiments show a parallel rate of forgetting for acoustically similar and control sequences, suggesting that the acoustic similarity effect does not occur during storage. Two input hypotheses are then examined, one involving a simple sensory trace, the other an overloading of a system which must both discriminate and memorize at the same time. Both predict that short-term memory for spoken word sequences should deteriorate when the level of background noise is increased. Subjects performed both a listening test and a memory test in which they attempted to recall sequences of five words. Noise impaired performance on the listening test but had no significant effect on retention, thus supporting neither of the input hypotheses. The final experiments studied two retrieval hypotheses. The first of these, Wickelgren's phonemic-associative hypotheses attributes the acoustic similarity effect to inter-item associations. It predicts that, when sequences comprising a mixture of similar and dissimilar items are recalled, errors should follow acoustically similar items. The second hypothesis attributes the effect to the overloading of retrieval cues which consequently do not discriminate adequately among available responses. It predicts maximum error rate on, not following, similar items. Two experiments were performed, one involving recall of visually presented letter sequences, the other of auditorily presented word sequences. Both showed a marked tendency for errors to coincide with acoustically similar items, as the second hypothesis would predict. It is suggested that the acoustic similarity effect occurs at retrieval and is due to the overloading of retrieval cues.     

Short-Term Forgetting of Order Under Conditions of Reduced Interference

Three experiments examined the short-term retention of order in a modified Brown-Peterson task. Our intent was to examine the loss of order memory, unconfounded by item memory, under conditions in which interference from prior trials is kept low. In previous work on the short-term forgetting of order, experimenters have tended to repeat the same items across trials or to draw from a restricted set; in our experiments, we changed the to-be-recalled items from trial to trial and used reconstruction as the retention measure. In all three experiments, very little forgetting was obtained across retention intervals that have traditionally produced dramatic and systematic loss. Our results are reminiscent of those obtained in the BrownPeterson task when performance is assessed after only the first experimental trial.     

Forgetting in immediate serial recall: decay, temporal distinctiveness, or interference?

Three hypotheses of forgetting from immediate memory were tested: time-based decay, decreasing temporal distinctiveness, and interference. The hypotheses were represented by 3 models of serial recall: the primacy model, the SIMPLE (scale-independent memory, perception, and learning) model, and the SOB (serial order in a box) model, respectively. The models were fit to 2 experiments investigating the effect of filled delays between items at encoding or at recall. Short delays between items, filled with articulatory suppression, led to massive impairment of memory relative to a no-delay baseline. Extending the delays had little additional effect, suggesting that the passage of time alone does not cause forgetting. Adding a choice reaction task in the delay periods to block attention-based rehearsal did not change these results. The interference-based SOB fit the data best; the primacy model overpredicted the effect of lengthening delays, and SIMPLE was unable to explain the effect of delays at encoding. The authors conclude that purely temporal views of forgetting are inadequate.     

Forgetting at short term: When do event-based interference and temporal factors have an effect?

Memory tasks combining storage and distracting tasks performed at either encoding or retrieval have provided divergent results pointing towards accounts of forgetting in terms of either temporal decay or event-based interference respectively. The aim of this study was to shed light on the possible sources of such a divergence that could rely on methodological aspects or deeper differences in the memory traces elicited by the different paradigms used. Methodological issues were explored in a first series of experiments by introducing at retrieval computer-paced distracting tasks that involved articulatory suppression, attentional demand, or both. A second series of experiments that used a similar design was intended to induce differences in the nature of memory traces by increasing the time allowed for encoding the to-be-remembered items. Although the introduction of computer-paced distracting tasks allowed for a strict control of temporal parameters, the first series of experiments replicated the effects usually attributed to event-based interference. However, deeper encoding abolished these effects while time-related effects remained unchanged. These findings suggest that the interplay between temporal factors and event-based interference in forgetting at short term is more complex than expected and could depend on the nature of memory traces.     

No retrieval-induced forgetting using item-specific independent cues: evidence against a general inhibitory account

Retrieval practice with particular items from memory can impair the recall of related items on a later memory test. This retrieval-induced forgetting effect has been ascribed to inhibitory processes (M. C. Anderson & B. A. Spellman, 1995). A critical finding that distinguishes inhibitory from interference explanations is that forgetting is found with independent (or extralist) cues. In 4 experiments, the authors tested whether the forgetting effect is cue-independent. Forgetting was investigated for both studied and unstudied semantically related items. Retrieval-induced forgetting was not found using item-specific independent cues for either studied or unstudied items. However, forgetting was found for both item types when studied categories were used as cues. These results are not in line with a general inhibitory account, because this account predicts retrieval-induced forgetting with independent cues. Interference and context-specific inhibition are discussed as possible explanations for the data.     

Short-term forgetting and the articulatory loop

Two experiments explored the role of subvocal articulatory rehearsal in the Peterson short-term forgetting task. In the first of these, subjects recalled consonant trigrams after an interval of 0, 5 or 15 s during which they either counted backwards in threes, suppressed articulation by continuously uttering the word “the”, or in a third control condition continuously tapped on the table. While counting backwards caused the usual dramatic forgetting, tapping caused no forgetting, and articulatory suppression only minimal forgetting at the longest delay. A second study used the same procedure but included only two conditions, articulatory suppression during the retention interval and articulatory suppression during both input and retention. Neither showed evidence of forgetting over the 15 s delay. These results suggest that covert speech is not necessary for rehearsal in short-term verbal memory. As such they call for a re-evaluation of the nature and function of rehearsal.     

Recognition-induced forgetting does not occur for temporally grouped objects unless they are semantically related

Recent evidence has shown that practice recognizing certain objects hurts memories of objects from the same category, a phenomenon called recognition-induced forgetting. In all previous studies of this effect, the objects have been related by semantic category (e.g., instances of vases). However, the relationship between objects in many real-world visual situations stresses temporal grouping rather than semantic relations (e.g., a weapon and getaway car at a crime scene), and temporal grouping is thought to cluster items in models of long-term memory. The goal of the present study was to determine whether temporally grouped objects suffer recognition-induced forgetting. To this end, we implemented a modified recognition-induced forgetting paradigm in which the objects were temporally clustered at study. Across four experiments, we found that recognition-induced forgetting occurred only when the temporally clustered objects were also semantically related. We conclude by discussing how these findings relate to real-world vision and inform models of memory.     

Retrieval-practice task affects relationship between working memory capacity and retrieval-induced forgetting

Retrieving a subset of items from memory can cause forgetting of other items in memory, a phenomenon referred to as retrieval-induced forgetting (RIF). Individuals who exhibit greater amounts of RIF have been shown to also exhibit superior working memory capacity (WMC) and faster stop-signal reaction times (SSRTs), results which have been interpreted as suggesting that RIF reflects an inhibitory process that is mediated by the processes of executive control. Across four experiments, we sought to further elucidate this issue by manipulating the way in which participants retrieved items during retrieval practice and examining how the resulting effects of forgetting correlated with WMC (Experiments 1–3) and SSRT (Experiment 4). Significant correlations were observed when participants retrieved items from an earlier study phase (within-list retrieval practice), but not when participants generated items from semantic memory (extra-list retrieval practice). These results provide important new insight into the role of executive-control processes in RIF.     

Cognitive control of familiarity: Directed forgetting reduces proactive interference in working memory

Proactive interference (PI) occurs when previously learned information interferes with new learning. In a working memory task, PI induces longer response times and more errors to recent negative probes than to new probes, presumably because the recent probe’s familiarity invites a “yes” response. Warnings, longer intertrial intervals, and the increased contextual salience of the probes can reduce but not eliminate PI, suggesting that cognitive control over PI is limited. Here we tested whether control exerted in the form of intentional forgetting performed during working memory can reduce the magnitude of PI. In two experiments, participants performed a working memory task with directed-forgetting instructions and the occasional presentation of recent probes. Surprise long-term memory testing indicated better memory for to-be-remembered than for to-be-forgotten items, documenting the classic directed-forgetting effect. Critically, in working memory, PI was virtually eliminated for recent probes from prior to-be-forgotten lists, as compared to recent probes from prior to-be-remembered lists. Thus cognitive control, when executed via directed forgetting, can reduce the adverse and otherwise persistent interference from familiarity, an effect that we attribute to attenuated memory representations of the to-be-forgotten items.     

Impaired verbal short-term memory in Down syndrome reflects a capacity limitation rather than atypically rapid forgetting

Individuals with Down syndrome suffer from relatively poor verbal short-term memory. Recent work has indicated that this deficit is not caused by problems of audition, speech, or articulatory rehearsal within the phonological loop component of Baddeley and Hitch's working memory model. Given this, two experiments were conducted to investigate whether abnormally rapid decay underlies the deficit. In a first experiment, we attempted to vary the time available for decay using a modified serial recall procedure that had both verbal and visuospatial conditions. No evidence was found to suggest that forgetting is abnormally rapid in phonological memory in Down syndrome, but a selective phonological memory deficit was indicated. A second experiment further investigated possible problems of decay in phonological memory, restricted to item information. The results indicated that individuals with Down syndrome do not show atypically rapid item forgetting from phonological memory but may have a limited-capacity verbal short-term memory system.     

Time-dependent forgetting in visual short-term memory

ABSTRACT

Whether visual short-term memory can be lost over an unfilled delay, in line with time-dependent forgetting, is controversial and prior work has yielded mixed results. The present study explored time-dependent forgetting in visual short-term memory in relation to other factors. In three experiments, participants compared single target and probe objects over a 2 s or 10 s retention interval. The objects across trials were either similar or dissimilar (Experiment 1) and had to be remembered in the presence of an additional distractor (Experiment 2) or under conditions where the amount of time separating trials varied (Experiment 3). In all experiments, the retention interval manipulation made the biggest contribution to performance, with accuracy decreasing as the retention interval was lengthened from 2 s to 10 s. These results pose problems for interference and temporal distinctiveness models of memory but are compatible with temporal forgetting mechanisms such as decay.     

The aftermath of memory retrieval for recycling visual working memory representations

We examined the aftermath of accessing and retrieving a subset of information stored in visual working memory (VWM)—namely, whether detection of a mismatch between memory and perception can impair the original memory of an item while triggering recognition-induced forgetting for the remaining, untested items. For this purpose, we devised a consecutive-change detection task wherein two successive testing probes were displayed after a single set of memory items. Across two experiments utilizing different memory-testing methods (whole vs. single probe), we observed a reliable pattern of poor performance in change detection for the second test when the first test had exhibited a color change. The impairment after a color change was evident even when the same memory item was repeatedly probed; this suggests that an attention-driven, salient visual change made it difficult to reinstate the previously remembered item. The second change detection, for memory items untested during the first change detection, was also found to be inaccurate, indicating that recognition-induced forgetting had occurred for the unprobed items in VWM. In a third experiment, we conducted a task that involved change detection plus continuous recall, wherein a memory recall task was presented after the change detection task. The analyses of the distributions of recall errors with a probabilistic mixture model revealed that the memory impairments from both visual changes and recognition-induced forgetting are explained better by the stochastic loss of memory items than by their degraded resolution. These results indicate that attention-driven visual change and recognition-induced forgetting jointly influence the “recycling” of VWM representations.     

Directed forgetting in pigeons resulting from the reallocation of memory-maintaining processes on forget-cue trials

When procedural artifacts are controlled, it has been difficult to demonstrate directed forgetting in pigeons. However, previous research with pigeons has not allowed for the reallocation of working memory (from forget items to remember items) on forget-cued trials as is possible in human directed forgetting experiments. In the present experiment, directed forgetting was found while controlling for procedural artifacts and allowing the pigeons to reallocate memory resources on forget trials. The results indicate that under these conditions, pigeons have active control over memory processing.     

Decomposing item-method directed forgetting of emotional pictures: Equivalent costs and no benefits

Using an item-method directed forgetting task, we presented negative, neutral, and positive photographic pictures, one at a time, each followed by an instruction to remember or forget. We determined that the directed forgetting effect, defined as better subsequent recognition of to-be-remembered (TBR) items than to-be-forgotten (TBF) items, was equivalent across negative, neutral, and positive pictures. To disentangle the underlying costs (i.e., decrease in memory for TBF items) and benefits (i.e., increase in memory for TBR items), we compared recognition memory performance in the directed forgetting task to that of a novel within-subjects remember-all control condition (Experiment 1) and to a between-subjects remember-all control group (Experiment 2). We observed costs without benefits across all three emotions—negative, neutral, and positive—in both experiments. These results demonstrate that equivalent directed forgetting effects for emotional stimuli are not attributable to different underlying component processes. Instead, our results suggest that selection for encoding is accomplished in similar ways, regardless of emotional content.     

Retrieval practice can eliminate list method directed forgetting

It has recently been shown that retrieval practice can reduce memories’ susceptibility to interference, like retroactive and proactive interference. In this study, we therefore examined whether retrieval practice can also reduce list method directed forgetting, a form of intentional forgetting that presupposes interference. In each of two experiments, subjects successively studied two lists of items. After studying each single list, subjects restudied the list items to enhance learning, or they were asked to recall the items. Following restudy or retrieval practice of list 1 items, subjects were cued to either forget the list or remember it for an upcoming final test. Experiment 1 employed a free-recall and Experiment 1 a cued-recall procedure on the final memory test. In both experiments, directed forgetting was present in the restudy condition but was absent in the retrieval-practice condition, indicating that retrieval practice can reduce or even eliminate this form of forgetting. The results are consistent with the view that retrieval practice enhances list segregation processes. Such processes may reduce interference between lists and thus reduce directed forgetting.     

Part-list reexposure and release of retrieval inhibition

In list-method directed forgetting, reexposure to forgotten List 1 items has been shown to reduce directed forgetting. proposed that reexposure to a few List 1 items only during a direct test of memory reinstates the entire List 1 episode. In the present experiments, part-list reexposure in the context of indirect as well as direct memory tests reduced directed forgetting. Directed forgetting was reduced when 50% or more of the items were reexposed, and was intact when only 25% were reexposed. Furthermore, part-list reexposure appeared to reinstate only reexposed items-not the entire List 1 episode.     

短时记忆定向遗忘的负荷效应:来自ERP的证据

采用事件相关电位(ERPs)技术,通过一个短时记忆测试,考察记忆/遗忘线索在不同的工作记忆负荷条件下诱发的脑电差异。实验以字母和数字为刺激,要求被试记忆或遗忘不同数量的视觉信息。ERP结果发现:在线索呈现230~430ms的时间窗口,高负荷条件的遗忘线索比低负荷条件的遗忘线索诱发了更正的ERPs。这一结果表明,抑制机制在定向遗忘中有重要作用,抑制不同数量的信息需要不同数量的认知资源。     

The nature and position of processing determines why forgetting occurs in working memory tasks

The effect of potentially distracting processing within working memory was examined by varying the nature and position of processing across conditions of a Brown-Peterson-like task. Separate groups of participants carried out verbal or visuospatial processing operations on identical stimuli, while retaining lists of to-be-remembered words. The number of words presented either before or after the processing interval was varied systematically. Results showed that although verbal processing was no more demanding than visuospatial processing, it led to greater forgetting. However, forgetting was confined to items presented prior to processing, and the difference in degree of forgetting shown by the two groups was maximal when four items occurred before processing. Temporal isolation effects were more marked in the verbal processing group. These findings indicate that individuals can keep active a limited number of items in primary memory during processing, unless processing blocks rehearsal, in which case retrieval occurs from secondary memory.     

Directed forgetting of visual symbols: Evidence for nonverbal selective rehearsal

Is selective rehearsal possible for nonverbal information? Two experiments addressed this question using the item method directed forgetting paradigm, where the advantage of remember items over forget items is ascribed to selective rehearsal favoring the remember items. In both experiments, difficult-to-name abstract symbols were presented for study, followed by a recognition test. Directed forgetting effects were evident for these symbols, regardless of whether they were or were not spontaneously named. Critically, a directed forgetting effect was observed for unnamed symbols even when the symbols were studied under verbal suppression to prevent verbal rehearsal. This pattern indicates that a form of nonverbal rehearsal can be used strategically (i.e., selectively) to enhance memory, even when verbal rehearsal is not possible.