Short-term memory in autism spectrum disorder

Three experiments examined verbal short-term memory in comparison and autism spectrum disorder (ASD) participants. Experiment 1 involved forward and backward digit recall. Experiment 2 used a standard immediate serial recall task where, contrary to the digit-span task, items (words) were not repeated from list to list. Hence, this task called more heavily on item memory. Experiment 3 tested short-term order memory with an order recognition test: Each word list was repeated with or without the position of 2 adjacent items swapped. The ASD group showed poorer performance in all 3 experiments. Experiments 1 and 2 showed that group differences were due to memory for the order of the items, not to memory for the items themselves. Confirming these findings, the results of Experiment 3 showed that the ASD group had more difficulty detecting a change in the temporal sequence of the items.     

Overt language production plays a key role in the Hebb repetition effect

When asked to recall verbatim a short list of items, performance is very limited. However, if the list of items is repeated across trials, recall performance improves. This phenomenon, known as the Hebb repetition effect (Hebb, 1961; Brain Mechanisms and Learning: A Symposium, pp. 37–51), is considered a laboratory analogue of language learning. In effect, learning a new word implies the maintenance of a series of smaller units, such as phonemes or syllables, in the correct order for a short amount of time before producing them. The sequence of smaller units is typically presented more than once. In the present study, we investigated the role of overt language production in language learning by manipulating recall direction. If the learning of a repeated list of items relies on overt language production processes, changing list production order by manipulating recall direction should impact the learning of the list. In Experiment 1, one list was repeated every third trial, and recall direction of the repeated list changed on the ninth repetition. In Experiment 1a, the repeated list changed from a forward to a backward order recall, where participants had to recall the items in reverse presentation order. In Experiment 1b, the repeated list changed from a backward to a forward order recall. Results showed a cost in recall performance for the repeated list when recall direction switched from forward to backward recall, whereas it was unaffected by the change from backward to forward recall. In Experiment 2, we increased the number of trials before introducing the change from a backward to a forward order recall. Results showed a decrement in recall performance for the repeated list following the change in recall direction, suggesting that language production processes play a role in the Hebb repetition effect.     

Word frequency effects in associative and item recognition

The word frequency effect (WFE) has been taken as evidence that recall and recognition are in some way fundamentally different. Consequently, most models assume that recall and recognition operate via very different retrieval mechanisms. Experiment 1 showed that the WFE reverses for associative recognition, which requires discrimination between intact test pairs and recombinations of study list words from different study pairs. Experiment 2, in which word triples were used, revealed an interaction between word frequency and test type: for item recognition, performance was better for low-frequency words; however, for associative recognition and free recall, performance was better for high-frequency words. In Experiment 3, item recognition was tested: although overall performance was better for low-frequency words, the recognition advantage for items in intact pairs was larger for high-frequency words, suggesting two components in recognition memory. These results imply common mechanisms in recall and recognition. Theoretical implications are discussed within the framework of the SAM model.     

Accurate monitoring leads to effective control and greater learning of patient education materials

Effective management of chronic diseases (e.g., diabetes) can depend on the extent to which patients can learn and remember disease-relevant information. In two experiments, we explored a technique motivated by theories of self-regulated learning for improving people's learning of information relevant to managing a chronic disease. Materials were passages from patient education booklets on diabetes from NIDDK. Session 1 included an initial study trial, Session 2 included self-regulated restudy, and Session 3 included a final memory test. The key manipulation concerned the kind of support provided for self-regulated learning during Session 2. In Experiment 1, participants either were prompted to self-test and then evaluate their learning before selecting passages to restudy, were shown the prompt questions but did not overtly self-test or evaluate learning prior to selecting passages, or were not shown any prompts and were simply given the menu for selecting passages to restudy. Participants who self-tested and evaluated learning during Session 2 had a small but significant advantage over the other groups on the final test. Secondary analyses provided evidence that the performance advantage may have been modest because of inaccurate monitoring. Experiment 2 included a group who also self-tested but who evaluated their learning using idea-unit judgments (i.e., by checking their responses against a list of key ideas from the correct response). Participants who self-tested and made idea-unit judgments exhibited a sizable advantage on final test performance. Secondary analyses indicated that the performance advantage was attributable in part to more accurate monitoring and more effective self-regulated learning. An important practical implication is that learning of patient education materials can be enhanced by including appropriate support for learners' self-regulatory processes.     

A motor isolation effect: When object manipulability modulates recall performance

Previous studies suggested that the language production architecture is recruited during verbal retention, and others proposed that spatial memory relies on the oculomotor system. The objective of the present study was to investigate the role of the motor system in object memory, by examining the effect of objects' affordances on retention. In a serial recall task, we manipulated the manipulability of objects to retain in memory. We used an isolation paradigm where we isolated the manipulability level of one object from the list. We showed that recall performance improved for the isolated object (Experiment 1) and that this advantage was abolished when participants were required to perform motor suppression during the task (Experiment 2). In Experiment 3, we showed that the abolition of the motor isolation effect in Experiment 2 was not due to an effect of distraction since motor suppression was shown not to interfere with a semantic isolation effect. It is argued that motor affordances play a role in object memory, but only when the motor characteristics of an object allow discriminating it from the other objects in the list.     

Repetition effects in directed forgetting: evidence for retrieval inhibition

Four experiments were conducted in support of a role for memory retrieval inhibition in directed forgetting. In each experiment, subjects were presented a list of words, some of which they were instructed to remember and some of which they were instructed to forget. After a recall test for all the words, the list was repeated. This time, however, all the words were presented with instructions that they be remembered. The improvement in recall from Trial 1 to Trial 2 was greater for the “forget” (F) words than for the “remember” (R) words. This difference was not due to a memorization-difficulty, item-selection effect (Experiment 2), a differential priority for rehearsal or output position given to the F items on Trial 2 (Experiment 3), or the greater number of F items left to be learned after Trial 1 (Experiment 4). Thus, the differential improvement from List 1 to List 2 for the F items was interpreted as a release of retrieval inhibition owing to the change in cue from forget to remember.     

Long-term proactive interference and novelty enhancement effect in monkey list memory

Serial-probe-recognition (SPR) performance by 2 monkeys deteriorated over several months of training. Three hundred and twenty different items were presented without repetition within a session (trial unique) but were repeated between sessions. The cause of the deterioration was identified as proactive interference (PI) due to repetitive use of items from day to day. Introduction of novel stimuli across days improved performance from 63% to 82% correct (Experiment 1). Tests with only probe items and no list items (Experiment 2) revealed that the monkeys were using a familiar/novel response strategy in combination with a relational strategy (relating the probe item to the list items) to further improve their SPR performance. Intermixing familiar baseline trials and novel transfer trials within a session (Experiment 3) encouraged the subjects to use a relational strategy, and it improved performance on baseline trials as well as on transfer trials. Possible qualitative similarity between the relational strategy and the familiar/novel response strategy is discussed along with theoretical implications of these findings for experiments which have used small number of repeating stimuli within a session.     

Aging and the Ranschburg effect: no evidence of reduced response suppression in old age

Two experiments tested 1 aspect of L. Hasher and R. T. Zacks's (1988) reduced inhibition hypothesis, namely, that old age impairs the ability to suppress information in working memory that is no longer relevant. In Experiment 1, young and older adults were asked to recall lists of letters in the correct order. Half of the lists contained repeated items while half were control lists. Recall of nonadjacent repeated items was worse than that of control items. This Ramschburg effect was larger (i.e., greater response suppression) in older than in young adults. In Experiment 2, young and older adults were required either to recall the list or to report if there was a repeated item. Repetition detection was high and similar in the 2 age groups. When age differences in overall performance were taken into account, there was evidence of increased repetition inhibition with age in both experiments. Thus, contrary to the general reduced inhibition hypothesis, the specific process of response suppression during serial recall is not reduced by aging.     

Testing effects in mixed- versus pure-list designs

In the present study, we investigated the role of list composition in the testing effect. Across three experiments, participants learned items through study and initial testing or study and restudy. List composition was manipulated, such that tested and restudied items appeared either intermixed in the same lists (mixed lists) or in separate lists (pure lists). In Experiment 1, half of the participants received mixed lists and half received pure lists. In Experiment 2, all participants were given both mixed and pure lists. Experiment 3 followed Erlebacher’s (Psychological Bulletin, 84, 212–219, 1977) method, such that mixed lists, pure tested lists, and pure restudied lists were given to independent groups. Across all three experiments, the final recall results revealed significant testing effects for both mixed and pure lists, with no reliable difference in the magnitude of the testing advantage across list designs. This finding suggests that the testing effect is not subject to a key boundary condition—list design—that impacts other memory phenomena, including the generation effect.     

Nonword repetition in lexical decision: Support for two opposing processes

We tested and confirmed the hypothesis that the prior presentation of nonwords in lexical decision is the net result of two opposing processes: (1) a relatively fast inhibitory process based on global familiarity; and (2) a relatively slow facilitatory process based on the retrieval of specific episodic information. In three studies, we manipulated speed-stress to influence the balance between the two processes. Experiment 1 showed item-specific improvement for repeated nonwords in a standard “respond-when-ready” lexical decision task. Experiment 2 used a 400-ms deadline procedure and showed performance for nonwords to be unaffected by up to four prior presentations. In Experiment 3 we used a signal-to-respond procedure with variable time intervals and found negative repetition priming for repeated nonwords. These results can be accounted for by dual-process models of lexical decision (e.g., Balota & Chumbley, 1984; Balota & Spieler, 1999).     

Automatization and training in visual search.

In several search tasks, the amount of practice on particular combinations of targets and distractors was equated in varied-mapping (VM) and consistent-mapping (CM) conditions. The results indicate the importance of distinguishing between memory and visual search tasks, and implicate a number of factors that play important roles in visual search and its learning. Visual search was studied in Experiment 1. VM and CM performance were almost equal, and slope reductions occurred during practice for both, suggesting the learning of efficient attentive search based on features, and no important role for automatic attention attraction. However, positive transfer effects occurred when previous CM targets were re-paired with previous CM distractors, even though these targets and distractors had not been trained together. Also, the introduction of a demanding simultaneous task produced advantages of CM over VM. These latter two results demonstrated the operation of automatic attention attraction. Visual search was further studied in Experiment 2, using novel characters for which feature overlap and similarity were controlled. The design and many of the findings paralleled Experiment 1. In addition, enormous search improvement was seen over 35 sessions of training, suggesting the operation of perceptual unitization for the novel characters. Experiment 3 showed a large, persistent advantage for CM over VM performance in memory search, even when practice on particular combinations of targets and distractors was equated in the two training conditions. A multifactor theory of automatization and attention is put forth to account for these findings and others in the literature.     

Odour and Proustian memory: reduction of context‐dependent forgetting and multiple forms of memory

In Experiment 1, the reintroduction of the same ambient odour (lemon or lavender) improved performance four weeks later in both free recall and recognition of a word list. This was a cross‐over design that allowed direct comparison between congruent and incongruent odour conditions. A further comparison with an additional group showed that memory was not improved by the presence of a different odour. Experiment 2 investigated the effect of two odour cues (lemon and lavender) in the same cross‐over design using three learning and memory tests: (1) free recall of a word list; (2) problem solving; and (3) spatial learning. While recall of the word list and spatial learning were best when the same odour was present at both learning and test, there was no such context‐dependent effect for the problem‐solving task. However, the presence of the lavender odour at test improved performance in the problem‐solving task, irrespective of the odour present at the first exposure. Thus although lavender had some effect on problem solving, we saw context‐dependent retrieval only in free recall and spatial learning. We discuss the implications of this dissociation. Copyright © 2001 John Wiley & Sons, Ltd.     

Detrimental influence of contextual change on spacing effects in free recall

Two experiments were conducted to determine the mechanism underlying the spacing effect in free-recall tasks. Participants were required to study a list containing once-presented words as well as massed and spaced repetitions. In both experiments, presentation background at repetition was manipulated. The results of Experiment 1 demonstrated that free recall was higher for massed items repeated in a different context than for massed items repeated in the same context, whereas free recall for spaced items was higher when repeated in the same context. Furthermore, a spacing effect was shown for words repeated in the same context, whereas an attenuated spacing effect was revealed for words repeated in a different context. These findings were replicated in Experiment 2 under a different presentation background manipulation. Both experiments seem to be most consistent with a model that combines the contextual variability and the study-phase retrieval mechanism to account for the spacing effect in free-recall tasks.     

Effects of talker, rate, and amplitude variation on recognition memory for spoken words

This study investigated the encoding of the surface form of spoken words using a continuous recognition memory task. The purpose was to compare and contrast three sources of stimulus variability--talker, speaking rate, and overall amplitude--to determine the extent to which each source of variability is retained in episodic memory. In Experiment 1, listeners judged whether each word in a list of spoken words was "old" (had occurred previously in the list) or "new." Listeners were more accurate at recognizing a word as old if it was repeated by the same talker and at the same speaking rate; however, there was no recognition advantage for words repeated at the same overall amplitude. In Experiment 2, listeners were first asked to judge whether each word was old or new, as before, and then they had to explicitly judge whether it was repeated by the same talker, at the same rate, or at the same amplitude. On the first task, listeners again showed an advantage in recognition memory for words repeated by the same talker and at same speaking rate, but no advantage occurred for the amplitude condition. However, in all three conditions, listeners were able to explicitly detect whether an old word was repeated by the same talker, at the same rate, or at the same amplitude. These data suggest that although information about all three properties of spoken words is encoded and retained in memory, each source of stimulus variation differs in the extent to which it affects episodic memory for spoken words.     

Effects of phonological similarity and concurrent irrelevant articulation on short-term-memory recall of repeated and novel word lists

The extent to which phonological similarity of list words impairs short-term-memory recall was investigated in two experiments. Experiment 1 showed that the phonological-similarity effect occurred both when list words were repeatedly sampled from a small set and when they were new on every trial, both when word-order information was required and when it was not. Furthermore, the adverse effect of phonological similarity on recall was apparent on the initial lists recalled, did not change over trials, and cannot be attributed to increasing levels of proactive inhibition across lists. In Experiment 2, subjects were required to count repeatedly to six during list presentation. Concurrent irrelevant articulation lowered recall and abolished the phonological similarity effect for both repeated and novel word lists.     

Retrieval dynamics in recognition and list discrimination: Further evidence of separate processes of familiarity and recall

Two experiments tested the hypothesis that the time course of retrieval from memory is different for familiarity and recall. The response-signal method was used to compare memory retrieval dynamics in yes-no recognition memory, as a measure of familiarity, with those of list discrimination, as a measure of contextual recall. Responses were always made with regard to membership in two previous study lists. In Experiment 1 an exclusion task requiring positive responses to words from one list and negative responses to new words and words from the nontarget list was used. In Experiment 2, recognition and list discrimination were separate tasks. Retrieval curves from both experiments were consistent, showing that the minimal retrieval time for recognition was about 100 msec faster than that for list discrimination. Repetition affected asymptotic performance but had no reliable effects on retrieval dynamics in either the recognition or the list-discrimination task.     

Adapting to an irrelevant item in an immediate recall task

Recall of the last one or two items of a spoken list is impaired when the list is followed by a nominally irrelevant item. At issue here was whether this suffix effect is reduced with repeated exposure to the irrelevant item. The effect was found to decline over successive blocks of trials, but only slightly (Experiment 1). No decisive evidence for adaptation to the irrelevant item was found when it was spoken after each of the list items rather than after the last one only (Experiments 2 and 3). The strongest evidence for adaptation was obtained when the irrelevant item was repeated in an unbroken stream that extended through the presentations and recall periods of successive lists: The recency effect and the level of recall at the last position within a list were greater under these conditions than when the irrelevant item was presented only once after each list (Experiments 4, 5, and 6).     

Recognition memory for words and pictures at short and long retention intervals

In two experiments, subjects studied a long series of words and pictures for recognition. Retention intervals varied from several minutes to a few months. The complicated testing procedures in Experiment I required the use of a traditional correction for guessing to obtain estimates of subjects' memory performance. A comparable, but simpler, design in Experiment II permitted the calculation of sensitivity and bias measures. In both studies, pictorial memory was superior to verbal memory at all retention intervals tested, and this advantage was essentially constant over time. In addition, the experiments identified an increasing tendency to call verbal test items "old" over time. Bias scores in Experiment H revealed that subjects adopted a more lenient criterion in responding to words than to pictures, and increased leniency was noted for both item types over time. Explanations of the results are offered in terms of differences in initial encoding and of a loss of discrimination between experimental and extraexperimental materials.     

Word repetitions in sentence recognition

When some items on a list are strengthened by extra study time or repetitions, recognition of other, unrelated, list items is not harmed (Ratcliff, Clark, & Shiffrin, 1990). Shiffrin, Ratcliff, and Clark (1990) accounted for this list-strength finding with a model assuming that different items are stored separately in memory, but that repetitions are accumulated together into a single stronger memory trace. Repeating words in the context of different sentences might cause separate storage of the repetitions of a given word, because either word or sentence traces are stored separately. Separate storage would, in effect, convert a list-strength manipulation into a list-length manipulation and thereby induce a positive list-strength effect. In Experiment 1, this result was produced for single-word recognition and for two types of sentence recognition. In Experiment 2, both words and sentences were repeated together, which should have caused repetitions to be stored in a single, stronger, trace. As expected, the list-strength effect was eliminated. A sentence trace model was fit to the data, supporting the account of Shiffrin et al. (1990) and supporting an account of word and sentence recognition in which activation is summed for representations of all list items. The results from the two studies are inconsistent with most current models of memory (as shown by the theoretical analyses of Shiffrin et al., 1990) and pose an additional challenge for theory.