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.
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 of activated 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.
We report three correlation studies, which investigate the hypothesis that individual differences in the capacity of a semantic short-term memory (STM) component in working memory (WM) predict performance on complex language tasks. To measure the capacity of semantic STM, we devised a storage-only measure, the conceptual span, which makes use of a category-cued recall procedure. In the first two studies, where the conceptual span was administered with randomized words (not blocked by categories), we found that conceptual span predicted single-sentence and text comprehension, semantic anomaly detection and verbal problem solving, explaining unique variance beyond non-word and word span. In some cases, the conceptual span explained unique variance beyond the reading span. Conceptual span correlated better with verbal problem solving than reading span, suggesting that a storage-only measure can outperform a storage-plus-processing measure. In Study 3, the conceptual span was administered with semantically clustered lists. The clustered span correlated with the comprehension measures as well as the non-clustered span, indicating that the critical process is memory maintenance and not semantic clustering. Moreover, we found an interaction between subjectsÕ performance on the conceptual span and the effect of the distance between critical words in anomaly detection, supporting the proposal that semantic STM maintains unintegrated word meanings. Ó 2002 Elsevier Science (USA). All rights reserved.Keywords: Short term memory; Working memory; Reading comprehension; Individual differences; Conceptual span; Reading span It is widely recognized that a limited-capacity working memory (WM) system plays an important role in complex cognition, supporting both the temporary storage and processing of information (for a review see Kintsch, Healy, Hegarty, Pennington, & Salthouse, 1999). A seminal study by Daneman and Carpenter (1980) demonstrated the importance of WM in the domain of language processing. Its major finding was that a storage-plus-processing measure of WM, the reading span, predicted accuracy of text comprehension (see also Baddeley, Logie, Nimmo-Smith, & Brereton, 1985;Budd, Whitney, & Turley, 1995;Daneman & Carpenter, 1983;Dixon, Le Fevre, & Twilley, 1989;Engle, Cantor, & Carullo, 1992;LaPointe & Engle, 1990;Masson & Miller, 1983), while a storage-only measure, the word span, did not (see also Turner & Engle, 1989). Moreover, when a statistically significant correlation between word span and comprehension is obtained, it tends to be smaller than the correlation between reading span and comprehension (LaPointe & Engle, 1990). The reading span test determines the number of sentence-final words a person can recall immediately after reading aloud a set of sentences and thus emphasizes both storage and processing of words. By contrast, the word span is a storage-only measure, which determines the number of 0749-596X/02/$ -see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII: S 0 7 4 9 -5 9 6 ...
Recently, several investigators have suggested that the parsing system of Broca's aphasics is affected by a resource limitation which could involve (1) a reduction in the size of a syntactic buffer, (2) slow activation of syntactic information, or (3) fast decay of syntactic information. The results of a syntactic-priming experiment, which varied the SOA (stimulus-onset asynchrony: 300, 700 and 1100 ms) between a prime fragment and target presented for lexical decision, provided support for the slow-activation hypothesis. A group of 13 age-matched controls showed syntactic priming, that is, significantly faster response times in the grammatical condition than in the ungrammatical condition, at all three SOAs. A group of 13 Broca's aphasics, on the other hand, showed significant syntactic priming only at the 110 ms SOA.
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