Free recall measures of short-term store: Are rehearsal and order of recall data necessary?

Several investigators have claimed that immediate free recall is a composite of output from two different storage systems—a short-term store (STS) and a long-term store (LTS). Free recall data and measures of STS were evaluated by having subjects report their rehearsals while lists of words were presented at a rate of one word every 1.25, 2.50, or 5.00 sec. The results support the conclusions that (a) arranging recall as a function of where an item was presented, rather than where it was rehearsed, is inappropriate to discussions of STS and LTS, and (b) computing measures of STS without both rehearsal and order of recall data yields a biased estimate of STS.

     

Semantic similarity dissociates short- from long-term recency effects: Testing a neurocomputational model of list memory

The finding that recency effects can occur not only in immediate free recall (i.e., short-term recency) but also in the continuous-distractor task (ie., long-term recency) has led many theorists to reject the distinction between short- and long-term memory stores. Recently, we have argued that long-term recency effects do not undermine the concept of a short-term store, and we have presented a neurocomputational model that accounts for both short- and long-term recency and for a series of dissociations between these two effects. Here, we present a new dissociation between short- and long-term recency based on semantic similarity, which is predicted by our model. This dissociation is due to the mutual support between associated items in the short-term store, which takes place in immediate free recall and delayed free recall but not in continuous-distractor free recall.     

The role of articulation in the parsing and retention of letter strings in tachistoscopic free recall

In Mewhort and Campbell's (1981) model of visual word recognition, a scan-parse mechanism transfer information from a character buffer to a short-term store and is largely responsible for the familiarity effects observed in tachistoscopic free recall. Although Mewhort and Campbell do not elaborate on the role of articulation in this task, they do suggest that the scan-parse mechanism acts prior to any involvement of articulatory processes (see Mewhort & Campbell, 1980). However, proponents of working memory (see Baddeley, 1986) are clear that articulation is necessary for the transfer of visual information to a phonological short-term store. In order to clarify the role of articulation in the parsing and retention of letter string, we asked subjects to undertake a tachistoscopic free-recall task, involving first- and fourth-order letter strings, with and without articulatory suppression and/or unattended speech. Unattended speech was observed to interfere with recall, but only when subjects were free to articulate the strings. This implies that subjects were retrieving information from the phonological store and that articulation is necessary for the registration of visual information in this store. The lack of interaction between order-of-approximation and suppression supports the view that the scan-parse mechanism acts independently of articulation. It appears, therefore, that letter strings are parsed at a stage preceding their transfer of the pharmacological store. Finally, the results indicate that subjects are able to draw directly on a representation of the parsed components of a letter string and may do so when phonological storage is difficult.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maintenance of semantic information in capacity-limited item short-term memory

We report a semantic effect in immediate free recall, which is localized at recency and is preserved under articulatory suppression but is highly reduced when recall is delayed after an intervening distractor task. These results are explained by a neurocomputational model based on a limited-capacity short-term memory (STM) store, consisting ofactivated long-term memory representations. The model makes additional predictions about serial position functions in semantically cued recall, indicating capacity limitations caused by a displacement type mechanism, which are confirmed in a second experiment. This suggests that in addition to the phonological component in verbal STM, there is an activation/ item-limited component with semantically sensitive representations.     

Articulatory rehearsal and phonological storage in working memory

The theoretical distinction between an articulatory control process and a short-term phonological store was supported in five experiments on immediate serial recall. In Experiment 1, articulatory suppression during the presentation and recall of auditory material abolished the word length effect but not the phonemic similarity effect. In Experiment 2, the two latter effects were found to be independent with auditory presentation. In Experiment 3, the effects of irrelevant speech and word length were found to be independent with visual presentation. In Experiment 4, articulatory suppression during the presentation and recall of auditory material abolished the phonemic similarity effect with a slow presentation rate. Nevertheless, in Experiment 5, articulatory suppression with a conventional presentation rate did not reduce the effect of phonemic similarity, even when a 10-sec interval was interposed between presentation and recall. These results indicate that the encoding, maintenance, and retrieval of spoken material within the phonological store do not depend on a process of articulatory rehearsal.     

Testing the Idea of Distinct Storage Mechanisms in Memory

This paper sets out quantitative foundations for testing the idea that memory is served by two distinct storage mechanisms, a short-term and a separate long-term store, using data from the single-trial free-recall experiment by Murdock and Okada (1970). In single-trial free recall one can observe which word is recalled next and how long that recall takes, but that is all. So justification for two separate stores must turn either on the probabilities of recall, or on the latencies, for particular serial positions in the stimulus list. (a) Nearly one-third of all recalls after the first are successors (Word n+1 immediately following recall of Word n). So recall is dominated, not by absolute serial position (as a short-term store would require), but by position relative to the preceding recall. (b) To a first approximation, all first recalls have the same latency distribution except for Word 1. A common latency distribution is compatible with a single store. An explanation is offered why Word 1 should take longer, in which Word 1 is the second retrieval from a common store. The idea of two separate stores appears to lack experimental support.     

A constrained Rasch model of trace redintegration in serial recall

The notion that verbal short-term memory tasks, such as serial recall, make use of information in long-term as well as in short-term memory is instantiated in many models of these tasks. Such models incorporate a process in which degraded traces retrieved from a short-term store are reconstructed, or redintegrated (Schweickert, 1993), through the use of information in long-term memory. This article presents a conceptual and mathematical model of this process based on a class of item-response theory models. It is demonstrated that this model provides a better fit to three sets of data than does the multinomial processing tree model of redintegration (Schweickert, 1993) and that a number of conceptual accounts of serial recall can be related to the parameters of the model.     

Phonological short-term store and the nature of the recency effect: Evidence from neuropsychology

The recency effect in immediate recall of lists of unrelated words was investigated in P.V., a left hemisphere-damaged patient, who had a grossly reduced auditory verbal span, attributed to a selective impairment of a phonological short-term store. No recency effect was evident in free recall of auditorily presented material. When the patient was instructed to recall the final items of the list first, the recency performance remained defective, even though P.V. was able to adopt a recall from end order. In the case of visual presentation, P.V.'s free recall performance was within the normal range and a clear recency occurred in the recall from end condition. These results are consistent with the view that the standard recency effect in immediate free recall of auditorily presented material represents the output of a phonological short-term store to which ordinal retrieval strategies, in P.V.'s case unimpaired, are applied. Finally, the contributions of the phonological short-term store and the process of rehearsal to the recency effect and to immediate memory span performance are discussed.     

The persistence of memory: Contiguity effects across hundreds of seconds

A contiguity effect-the finding that stimuli that occur close together in time become associated to each other--is observed between words that are separated by several seconds. The traditional account of contiguity effects is that item representations become associated to each other while active in a short-term memory buffer--a limited-capacity store that can hold a small, integral number of items. Participants studied and free recalled 48 lists of words. At the end of the session, participants were given a surprise final free recall test on all of the items from all of the lists. In addition to a standard contiguity effect between items presented at nearby serial positions, we simultaneously observed a contiguity effect between items presented in different lists. This latter contiguity effect extended over several lists, or several hundred seconds, well beyond the range that can be attributed to a buffer holding a small, integral number of items.     

Eye movements under different rehearsal strategies.

Eye movements were recorded while subjects studied lists of simultaneously presented words. The 24 subjects in the storage group studied for immediate recall, and the 24 subjects in the coding group studied primarily for a later, final recall. Those subjects in the coding group had longer eye fixations and fewer regressions than did subjects in the storage group. In addition, the subjects in the coding group recalled fewer words in immediate recall and more words in final recall than did the subjects in the storage group. These results were interpreted as supporting the elaboration hypothesis of coding in rehearsal, which states that coding into long-term store consists of rehearsing both old and new information in short-term store. The results did not support the concentration hypothesis, which states that coding into long-term store consists of intensively rehearsing a smaller number of items than rehearsed under a storage strategy. The eye movement data also indicate that subjects read about twice as many words as they overtly rehearse.     

The demise of short-term memory revisited: empirical and computational investigations of recency effects

In the single-store model of memory, the enhanced recall for the last items in a free-recall task (i.e., the recency effect) is understood to reflect a general property of memory rather than a separate short-term store. This interpretation is supported by the finding of a long-term recency effect under conditions that eliminate the contribution from the short-term store. In this article, evidence is reviewed showing that recency effects in the short and long terms have different properties, and it is suggested that 2 memory components are needed to account for the recency effects: an episodic contextual system with changing context and an activation-based short-term memory buffer that drives the encoding of item-context associations. A neurocomputational model based on these 2 components is shown to account for previously observed dissociations and to make novel predictions, which are confirmed in a set of experiments.     

A context-based theory of recency and contiguity in free recall

The authors present a new model of free recall on the basis of M. W. Howard and M. J. Kahana's temporal context model and M. Usher and J. L. McClelland's leaky-accumulator decision model. In this model, contextual drift gives rise to both short-term and long-term recency effects, and contextual retrieval gives rise to short-term and long-term contiguity effects. Recall decisions are controlled by a race between competitive leaky accumulators. The model captures the dynamics of immediate, delayed, and continual distractor free recall, demonstrating that dissociations between short- and long-term recency can naturally arise from a model in which an internal contextual state is used as the sole cue for retrieval across time scales.     

The effects of word co-occurrence on short-term memory: associative links in long-term memory affect short-term memory performance

In immediate serial recall tasks, high-frequency words are recalled better than low-frequency words. This has been attributed to high-frequency words' being better represented and providing more effective support to a redintegration process at retrieval (C. Hulme et al., 1997). In studies of free recall, there is evidence that frequency of word co-occurrence, rather than word frequency per se, may explain the recall advantage enjoyed by high-frequency words (J. Deese, 1960). The authors present evidence that preexposing pairs of low-frequency words, so as to create associative links between them, has substantial beneficial effects on immediate serial recall performance. These benefits, which are not attributable to simple familiarization with the words per se, do not occur for high-frequency words. These findings indicate that associative links between items in long-term memory have important effects on short-term memory performance and suggest that the effects of word frequency in short-term memory tasks are related to differences in interitem associations in long-term memory.     

Irrelevant sound disrupts speech production: Exploring the relationship between short-term memory and experimentally induced slips of the tongue

To explore the relationship between short-term memory and speech production, we developed a speech error induction technique. The technique, which was adapted from a Japanese word game, exposed participants to an auditory distractor word immediately before the utterance of a target word. In Experiment 1, the distractor words that were phonologically similar to the target word led to a greater number of errors in speaking the target than did the dissimilar distractor words. Furthermore, the speech error scores were significantly correlated with memory span scores. In Experiment 2, memory span scores were again correlated with the rate of the speech errors that were induced from the task-irrelevant speech sounds. Experiment 3 showed a strong irrelevant-sound effect in the serial recall of nonwords. The magnitude of the irrelevant-sound effects was not affected by phonological similarity between the to-be-remembered nonwords and the irrelevant-sound materials. Analysis of recall errors in Experiment 3 also suggested that there were no essential differences in recall error patterns between the dissimilar and similar irrelevant-sound conditions. Weproposed two different underlying mechanisms in immediate memory, one operating via the phonological short-term memory store and the other via the processes underpinning speech production.     

Examining the relationship between free recall and immediate serial recall: the effect of concurrent task performance

In 3 experiments, participants saw lists of 16 words for free recall with or without a 6-digit immediate serial recall (ISR) task after each word. Free recall was performed under standard visual silent and spoken-aloud conditions (Experiment 1), overt rehearsal conditions (Experiment 2), and fixed rehearsal conditions (Experiment 3). The authors found that in each experiment, there was no effect of ISR on the magnitude of the recency effect, but interleaved ISR disrupted free recall of those words that would otherwise be rehearsed. The authors conclude that ISR and recency cannot both be outputs from a unitary limited-capacity short-term memory store and discuss the possibility that the process of rehearsal may be common to both tasks.     

The long-term recency effect in recognition memory

Three classes of theories explain the recency effect: the modal model, single-store models, and the composite view, which integrates the two positions. None could explain the absence of a long-term recency effect in recognition memory in previous studies. We suggest that prior work did not obtain a recency effect because testing used a multiple-probe rather than a single-probe recognition procedure. Here we tested memory using a single-probe recognition procedure. Experimental conditions included an immediate test, a delayed test after a filled interval, and a continuous-distractor paradigm in which the same filled delay preceded the first word and followed every study word. The long-term recency effect in continuous-distractor recognition was equivalent to the recency effect in immediate recognition. Its absence in the delayed recognition condition demonstrated that it was not attributed to the use of a putative short-term memory store. Single-store models and the composite view can account for this novel finding.     

Developing the theory of working memory

The theory of working memory was devised to explain the effects of a concurrent memory load in various experimental situations in terms of the operation of a central executive processor and a phonemic response buffer. It also explains the effects of phonemic similarity, articulatory suppression, word length, and unattended speech. Experiment 1 demonstrated that a concurrent memory load markedly reduced the phonemic similarity effect in immediate serial recall, which was taken to support the concept of a limited-capacity phonemic response buffer. A more detailed analysis of the results suggested that a concurrent memory load may affect the storage capacity of the central executive processor and the translation of orthographic stimuli into phonological representations, as well as the storage capacity of the phonemic response buffer. Experiment 2 showed that a concurrent free-recall task reduced the phonemic similarity effect in immediate serial recall, but only in the case of visually presented sequences of items. Moreover, unattended speech was found to have no effect upon performance in immediate free recall. These results were taken to imply that the phonemic response buffer contributes only to performance in cognitive tasks that require the accurate retention of serial-order information.     

单字法有意遗忘的内部心理机制：基于多项式加工树模型的分析

通过构建使用单个双字词作为实验材料,并在测验阶段全面考察记忆提取过程的MPT模型,考察单字法有意遗忘的心理机制。结果发现,对于TBF/R项目,遗忘组的储存能力和提取能力均弱于记忆组;对于TBR/R项目,遗忘组的储存能力强于记忆组。并且无论对于短时SOA还是长时SOA,遗忘组对TBF项目后探测刺激的反应时都显著长于TBR项目。研究表明,单字法有意遗忘现象是由选择性复述、注意抑制和提取抑制三种机制共同作用的结果。     

Initial-retrieval “depth” and the negative recency effect

A novel variation of the probed recall, negative recency paradigm was employed to test the general hypothesis that the amount of learning from an initial recall test is a function of the level of processing used during initial retrieval, and to test specific predictions concerning the role of initial tests in the production and elimination of the negative recency effect. On each of 32 trials, 32 subjects each saw four words followed by a search-mode signal and a probe word. The level of initial retrieval processing (acoustic or semantic) was controlled by the search-mode signal. Initial test response latencies were recorded, and the learning derived from initial tests was assessed by an unexpected final free recall test. Final recall of words initially retrieved in the semantic-search condition showed no negative recency, while final recall of words initially retrieved in the acoustic-search condition did show negative recency. Conditional analyses showed that memory was incremented more by semantic-level initial retrieval than by acoustic-level initial retrieval. Implications of these results for an explanation of negative recency effects and for other learning-from-tests effects are discussed.     

Maintaining recency despite a stimulus suffix

Two processes of information retrieval were considered in the context of the logogen model. The aim was to establish whether information about the final items of an auditory short-term memory list is held exclusively in precategorical acoustic storage at presentation or whether these items are automatically registered in a cognitive store as well. Error data for a final heterogeneous item in alphanumeric lists showed significantly better recall, despite the addition of a stimulus suffix. Although these results demonstrated that coding had proceeded further than a precategorical stage, which maintains only physical features, the possibility remained that the effect was due to a bias in focal attention and selective coding at list presentation. A second experiment increased the difficulty of the retrieval task, and effectively precluded the possibility of a bias in attention. The results confirmed the findings in the first experiment. It was concluded that information about the final item(s) is registered automatically in the cognitive system, and that responses are made available from this source when information about physical features of the item is degraded by a stimulus suffix.