The mirror effect and attention-likelihood theory: a reflective analysis.

The mirror effect refers to findings from studies of recognition memory consistent with the idea that the underlying "strength" distributions are symmetric around their midpoint separating studied and nonstudied items. Attention-likelihood theory assumes underlying binomial distributions of marked features and claims that old-item differences result from differential attention across conditions during study. The symmetry arises because subjects use the likelihood ratio as the basis for decision. The author analyzes the model and argues that one of the main criticisms (the complexity of the likelihood-ratio decision rule) is unwarranted. A further analysis shows that other distributions (the Poisson and the hypergeometric) can also produce a mirror effect. Even with the binomial distribution, a variety of parameter values can produce a mirror effect, and with the right combination of parameter values, differential attention across conditions is not necessary for a mirror effect to occur.

Developing TODAM: three models for serial-order information.

TODAM2, a theory of distributed associative memory, shows how item and associative information can be considered special cases of serial-order information. Consequently, it is important to get the right model for serial-order information. Here, we analyze and compare three distributed-memory models for serial-order information that use TODAM's convolution-correlation formalism. These models are the chaining model, the chunking model, and a new model, the power-set model. The chaining model associates each item with its predecessor; the chunking model uses multiple convolutions and n-grams to form chunks; and the power-set model interassociates all items in a set in a particular way to form a chunk. The models are compared in terms of their performance on seven basic tests of serial-order information--namely, serial recall, backward recall, recall of missing items, sequential probe tests, positional probe tests, serial-to-paired-associate transfer, and item recognition. The strengths and weaknesses of each model are discussed.

TODAM2: a model for the storage and retrieval of item, associative, and serial-order information.

This article presents an extended version of the convolution-correlation memory model TODAM (theory of distributed associative memory) that not only eliminates some of the inadequacies of previous versions but also provides a unified treatment of item, associative, and serial-order information. The chunking model extended the basic convolution-correlation formalism by using multiple convolutions, n-grams (multiple autoassociations of sums of item vectors), and chunks (sums of n-grams) to account for chunking and serial organization. TODAM2 extends the chunking model by including rn-grams (reduced n-grams), labels, and "lebals" (the involution or mirror image of a label) to provide a general model for episodic memory. For paired associates, it is assumed that subjects store only labeled n-grams and lebaled rn-grams. It is shown that the model is broadly consistent with a number of major empirical paired-associate and serial-order effects.

Output and retrieval interference in the missing-number task.

Three experiments are reported that represent a reexamination of the missing-number method (Buschke, 1963b) of estimating short-term memory span. The missing-number task involved presenting a random sequence of all but one of the numbers of a known reference set and asking subjects to identify the missing number. Experiment 1 introduced a modified missing-number task that included two missing items and two choices made by the subject. With a large decline in performance for the second choice relative to the first, it is possible that only the second choice was subject to output or retrieval interference. An alternative explanation is that subjects output the number with the weakest memory representation as their first response. By postcuing subjects to report their two choices in a forward or backward sequence, Experiment 2 provided evidence against the importance of output interference and support either for the importance of retrieval interference or for the "weakest-first" hypothesis. However, with a paradigm that replaced only correctly identified missing numbers, a prediction that subjects would select the number with the weakest memory representation as their first response was not confirmed in Experiment 3. Instead, retrieval interference was implicated to explain the first-choice superiority found in Experiments 1 and 3. The results were interpreted in terms of the TODAM model of Murdock (1982, 1987, in press).

The role of auditory features in memory span for words.

In two experiments on the effects of modality on memory span for words, conventional measures of span were supplemented by analyses of serial position curves and by analyses of the principal auditory features of intrusion errors. Auditory presentation led not only to better recall of the terminal words in each stimulus list but also to better recall of word order given correct item recall. Intrusion errors were found to share a number of auditory features with the corresponding omissions, even when the lists had been presented visually. The most salient or the best-retained word features were the syllabic stress pattern and the identity of the stressed vowel phoneme. The data provide evidence for a partial retention of auditory features of stimulus words in short-term memory tasks and are taken to support attribute rather than unit models of short-term memory.

The effect of a subsidiary task on iconic memory.

Using a subsidiary task technique, Doest and Turvey (1971) concluded that iconic memory was independent of the central processing system. However, they did not control the timing between the short-term memory and the iconic-memory tasks in their first experiment and they used a rather long stimulus duration in their second experiment. These procedural difficulties were rectified here in Experiments I and II. It was found that memory load reduced partial report at all interstimulus intervals and there was no interaction. The results of Experiment I were replicated with auditory presentation in Experiment III, ruling out a masking interpretation. Experiment IV ruled out an interpretation in terms of rehearsal or response competition. It was concluded that iconic memory, like short-term memory, is dependent on the central processing system in the sense that it will suffer in a subsidiary-task situation. The locus of the interference effect appears to be in the encoding stage.

The effects of visual presentation method on single-trial free recall.

In two experiments four different conditions of visual presentation were studied with the purpose of furthering our understanding of the role of temporal and spatial factors underlying modality effects in single-trial free recall. Enriching spatial factors in the visual presentation did not produce a higher performance in the recency part of the serial-position curve, and it was therefore concluded that the modality effect could not be due to any visual handicap. A lag distribution measure was suggested and applied to the data to characterize output order (the order of recall) in single-trial free recall. The two experiments carried out used a within-subjects and a between-subjects design, respectively, and illustrate the importance of the methodological difference between these two designs.