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Biomedical subjects

R M Shiffrin

Publications and source records attributed to R M Shiffrin.

33 records · Page 2Linked to original sources
PubMed1986

Retrieval strategies in recall of natural categories and categorized lists.

Experiments 1 and 2 examined the effect of retrieval strategies on 3 or 12 min of recall from a natural category. Experiment 3 examined the effect of strategy on 6 min of recall from a subset of a category presented as a list. In Experiments 1 and 2, a large recall deficit was produced by retrieval strategies involving recall in alphabetic order and by size of the words' referents, relative to free recall. In Experiment 3, four strategies, alphabetic, size, serial order, and free recall, gave similar levels of recall after 6 min, though the growth rate of the cumulative output functions differed among the strategies. An extension of the search of associative memory (SAM) model of Raaijmakers and Shiffrin was developed to explain these results; the new model postulates attention sharing among probe cues and the use of idiosyncratic strategies for free recall from natural categories.

Adolescent↗
PubMed1985

Building permanent memory codes: codification and repetition effects in word identification.

The studies presented in this article investigate the memory processes that underlie two phenomena in threshold identification: word superiority over pseudowords and the repetition effect (a prior presentation of an item facilitates later identification of that item). Codification (i.e., the development of a single memory code that can be triggered even by fragmented input information) explains the faster and more accurate identification of words than pseudowords. Our studies trace the development and retention of such codes for repeated pseudowords and examine the growth and loss of the repetition effect for both pseudowords and words. After approximately five prior occurrences, words and pseudowords are identified equally accurately in two types of threshold identification tasks, suggesting codification has been completed for pseudowords. Although the initial word advantage disappears, the accuracy of identification still increases with repetitions. The facilitation caused by repetition is not affected much by spacing within a session, but drops from one day to the next, and after a delay of one year has disappeared (new and old words were identified equally well). These results suggest an episodic basis for the repetition effect. Most important, after one year, performance is equal for old pseudowords and new and old words: all these levels are superior to that for new pseudowords, suggesting that the learned codes for pseudowords are as strong and permanent as the codes for words. A model of identification is presented in which feedback from codes and episodic images in memory facilitates letter processing. An instantiation of the model accounts for the major features of the data.

Attention↗
PubMed1985

Memory codes and episodes in models of word identification: a reply to Johnston, van Santen, and Hale.

We suggest that the activation model of identification benefits for repeated words and pseudowords proposed by Johnston, van Santen, and Hale (1985) is a variant of our own code/episode model (Salasoo, Shiffrin, & Feustel, 1985), used to explain the temporary and long-lasting effects of repetitions. In particular, Johnston et al.'s X and Y factors may reflect the operation of episodic memory traces and codification, respectively. Computational processing models, we believe, are useful because their precision helps clarify otherwise fuzzy theoretical distinctions.

Humans↗
PubMed1982

Forward masking of diotic and dichotic clicks by noise.

The first experiment reported here measured thresholds for clicks in forward masking as a function of the masker level and as a function of the temporal relation of a 6-kHz low-pass noise masker to the click (300-msec duration with a 20-msec temporal gap or 10-msec duration with a 5-msec gap). Also varied were the spectral content of the click (low-pass filtered at 1 or 5 kHz) and the interaural phase of the click (0 or pi). The difference in frequency content had no effect on the amount of masking for the 300-msec masker, while with the 10-msec masker greater masking was found for the 1-kHz click. This combination (1 kHz, 10 msec) was also the only one to produce Masking Level Differences (MLDs) when the click was presented dichotically. A second experiment investigated the effects of combining the maskers used in the first experiment. Additional masking (above that predicted by an energy sum) was found, as has been reported elsewhere [Penner and Shiffrin, A. Acoust. Soc. Am. 67, 617-627 (1980)]. However, the magnitude of this additional masking was decreased for certain conditions. These data conflict with the predictions of additivity of masking obtained from a model proposed by Penner and Shiffrin and suggest that modifications to that model are needed. The results of both experiments can be explained by assuming that two processes are acting in forward masking [Duifhuis, J. Acoust. Soc. Am. 54, 1471-1488 (1973)].

Acoustic Stimulation↗
PubMed1980

Nonlinearities in the coding of intensity within the context of a temporal summation model.

A model of temporal summation and intensity coding relates the subject's internal percept y(t) to the stimulus input x(t) by the equation y(t) = g(St - oof[x(tau)] h [t, tau, x (tau)]d tau). In words, some transformation f[x (t)] of the stimulus intensity is weighted by a function h and integrated; the result is transformed into the internal percept by a function g. This system postulates a linear integral operator preceded and followed by transformations which may be nonlinear. Based on forward masking of clicks by white noise, we (1) show that the above characterization of the model is appropriate (which involves showing that there is a linear temporal summation stage), and (2) derive certain characteristics of the system's nonlinearities. In particular, the integral of h times f is shown to be a nonlinear function of the input intensity exhibiting more compression than a power function. It is also shown that h must depend upon the intensity of the stimulus.

Auditory Perception↗
PubMed1976

Attending to forty-nine spatial positions at once.

Simultaneous attention to 49 spatial positions resulted in the processing of threshold information from one of those positions essentially identical to the processing when the subject knew in advance that that position would be tested. This result held true when the task consisted of detection of the presence of a briefly presented dot. The same result held true for 9 spatial positions when the task consisted of report of the briefly presented letter in the target position.

Attention↗
PubMed1970

Forgetting: trace erosion or retrieval failure?

A series of lists of random words was presented. Following each list, the subject attempted to recall the words of the list prior to the list just presented. Recall probability for a given word depended on the length of the list in which it was embedded, not on the length of the list intervening between presentation and test. These results indicate that forgetting is a failure in the memory search during retrieval rather than a degradation of the memory trace occurring between presentation and test.

Humans↗