Memory skills mediating superior memory in a world-class memorist

Laboratory studies have investigated how individuals with normal memory spans attained digit spans over 80 digits after hundreds of hours of practice. Experimental analyses of their memory skills suggested that their attained memory spans were constrained by the encoding time, for the time needed will increase if the length of digit sequences to be memorised becomes longer. These constraints seemed to be violated by a world-class memorist, Feng Wang (FW), who won the World Memory Championship by recalling 300 digits presented at 1 digit/s. In several studies we examined FW’s memory skills underlying his exceptional performance. First FW reproduced his superior memory span of 200 digits under laboratory condition, and we obtained his retrospective reports describing his encoding/retrieval processes (Experiment 1). Further experiments used self-paced memorisation to identify temporal characteristics of encoding of digits in 4-digit clusters (Experiment 2), and explored memory encoding at presentation speeds much faster than 1 digit/s (Experiment 3). FW’s superiority over previous digit span experts is explained by his acquisition of well-known mnemonic techniques and his training that focused on rapid memorisation. His memory performance supports the feasibility of acquiring memory skills for improved working memory based on storage in long-term memory.     

Cross‐Linguistic Differences in Digit Memory Span

This study investigated whether the better performance of the Chinese in digit memory span tasks was due only to the shorter pronunciation duration of Chinese digit names, or to enhanced visuospatial sketchpad abilities, or to both. Results of the experiment showed that the Chinese outperformed their Malay counterparts in digit memory span tasks because Chinese digit names had shorter pronunciation durations than Malay digit names and not because the Chinese had better visuospatial sketchpad abilities than the Malays. The results thus support Baddeley's phonological loop hypothesis as an account for cross‐linguistic differences in digit memory spans. Because memory traces are subject to decay and the phonological store is temporally limited, the shorter the pronunciation duration of digit names in a language, the more digits one can rehearse within a limited time period, and therefore the larger is one's short‐term digit span in that language.     

One percent ability and ninety-nine percent perspiration: a study of a Japanese memorist

In 1987, Hideaki Tomoyori, a Japanese memorist, set a world record for reciting the first 40,000 digits of pi. The authors report results from a series of tests that give a view of Tomoyori's memory performance compared with that of a control group, matched for age and educational level. He showed very good scores on tasks with digits, such as digit memory span tasks and 5 x 5 number matrix learning, although some of the control participants were nearly as good. In contrast, his performance was not particularly good for learning word lists and story recall. Overall, his performance on the tasks does not suggest that he has superior cognitive abilities. We believe that his extraordinary memory performance in reciting the digits of pi results from his effective use of a combination of digit-syllable transformations and imagery mnemonics developed from extensive practice. These results are consistent with the skilled memory framework.     

Midazolam amnesia and short-term/working memory processes

We examined whether midazolam impairs short-term/working memory processes. We hypothesize that prior dissociations in midazolam's effects on short-term/working memory tasks and episodic memory tasks arise because midazolam has a larger effect on episodic memory processes than on short-term/working memory processes. To examine these issues, .03 mg/kg of participant's bodyweight of midazolam was administered in a double-blind placebo-controlled within-participant design. Performance on the digit span and category generation/recall tasks was examined. The results of Experiment 1 demonstrated that: (1) midazolam impaired performance on the digit span task; (2) midazolam did not impair performance on the category generation task; (3) midazolam impaired performance on the category recall task; and (4) midazolam's effect on category recall was four times as large as its effect on digit span. The results of Experiment 2 demonstrated that midazolam did not impair digit span performance when the digit span task was administered at a later time. These results suggest that midazolam can impair short-term/working memory processes, but these effects are substantially smaller than midazolam's effect on episodic memory processes. Moreover, they demonstrate that conscious awareness of materials during study is not sufficient to produce episodic memory.     

The phonological loop and memory for rhythms: an individual differences approach

The purpose of the current study was to examine the relationship between short-term memory for rhythm and the phonological loop in working memory. Results showed that digit span scores significantly correlated with the scores on the rhythmic memory task, and that the correlation between the two scores remained significant even after the common variance with reading speed was partialled out. Partial correlation and regression analyses indicated that the relation between memory for rhythm and digit span scores is mediated by the third component in the phonological loop, the component that is responsible for regulation of timing mechanisms in immediate memory tasks.     

Individual differences in sentence memory

Results from an experiment with two parts are presented in this paper. In part one, participants listened to sentences containing two, three, four, or five clauses, and were asked questions about the content of the sentences. The results of part one demonstrate that an important unit of representation in sentence memory is the clause, and not some other component of discourse structure. In part two, the same group of participants performed eight different short-term storage/working memory tasks. A composite complex span score was computed for each participant based on three working memory tasks closely based on Daneman & Carpenter's (1980) reading span task. This working memory measure was significantly correlated with the participants' performance on the sentence memory task in part one. A second working memory measure—N-back—was also significantly correlated with the participants' performance on the sentence memory task, and there was no correlation between their performance on the complex span task and the N-back task. It is therefore concluded that (i) working memory consists of a number of dissociable components; and (ii) memory for sentences taps into more than one of these working memory components. Furthermore, the high correlations of sentence memory with the complex span and the N-back tasks (neither of which are language processing tasks) suggests that memory for sentences is not simply a result of linguistic experience; rather, it is likely that an independent working memory component contributes to participants' performance on the sentence memory task.     

How does the severity of a learning disability affect working memory performance?

Working memory performance was examined in children aged 11-12 years who had borderline, mild, and moderate learning disabilities. Comparisons with children of average abilities were used to determine whether those with more severe learning disabilities had greater impairments in working memory. Seven measures of working memory span were used to assess temporary phonological short-term storage (digit span, word span), temporary visuo-spatial short-term storage (pattern span, spatial span), and temporary short-term storage with additional processing, or central executive, demands (listening span, odd one out span, reverse digit span). Children with mild and moderate learning disabilities were impaired on all measures of working memory compared to children of average abilities. Children with borderline learning disabilities were just as good as children with average abilities on visuo-spatial and complex span tasks, but showed an impairment on phonological span tasks. Children with moderate learning disabilities were indistinguishable from children with mild learning disabilities on simple span tasks, but were significantly poorer than the mild group on the more demanding complex span tasks. For the group as a whole, working memory was strongly related to mental age.     

How does the severity of a learning disability affect working memory performance?

Working memory performance was examined in children aged 11-12 years who had borderline, mild, and moderate learning disabilities. Comparisons with children of average abilities were used to determine whether those with more severe learning disabilities had greater impairments in working memory. Seven measures of working memory span were used to assess temporary phonological short-term storage (digit span, word span), temporary visuo-spatial short-term storage (pattern span, spatial span), and temporary short-term storage with additional processing, or central executive, demands (listening span. odd one out span, reverse digit span). Children with mild and moderate learning disabilities were impaired on all measures of working memory compared to children of average abilities. Children with borderline learning disabilities were just as good as children with average abilities on visuo-spatial and complex span tasks, but showed an impairment on phonological span tasks. Children with moderate learning disabilities were indistinguishable from children with mild learning disabilities on simple span tasks, but were significantly poorer than the mild group on the more demanding complex span tasks. For the group as a whole, working memory was strongly related to mental age.     

Do young children rehearse? An individual-differences analysis

The issue of whether young children rehearse in auditory memory tasks was investigated across a series of three studies comparing individual differences in articulation rates and memory spans. Applying the principles of the working-memory model, children with faster rates of speaking should have superior memory spans if they engage in rehearsal. Two of the experiments, with 4-year-old children, failed to establish any significant association between articulation rate and memory span, although both the memory span and articulation rate procedures were found to be highly reliable in this age group A third experiment confirmed that, as expected, articulation rates and memory spans were significantly associated with one another in adult subjects. The results indicate that, contrary to recent theories of children’s short-term-memory development, 4-year-old children do not engage in subvocal rehearsal during auditory memory span tasks.     

Short-term memory performances during sustained wakefulness in patients with obstructive sleep apnea-hypopnea syndrome

Both working and immediate memories were assessed every 4h by specific short-term memory tasks over sustained wakefulness in 12 patients with obstructive sleep apnea and hypopnea syndrome (OSAHS) and 10 healthy controls. Results indicated that OSAHS patients exhibited lower working memory performances than controls on both backward digit span and complex Sternberg tasks. Speed and accuracy on Sternberg tasks were affected by memory load in both groups. However, immediate memory was not impaired in OSAHS patients. Diurnal and nocturnal SaO(2) were correlated with speed and accuracy high-speed memory scanning performance on Sternberg tasks in patients. These results suggest specific working memory deficits associated with OSAHS over sustained wakefulness with a possible deficiency in the central executive responsible for the higher information processing, in addition to a potentially insufficient storage capacity. Among OSAHS patients, working memory ability involved in high-speed memory scanning may be impaired by chronic hypoxemia.     

Interference in immediate spatial memory

It has been suggested that maintenance in visuospatial immediate memory involves implicit motor processes that are analogous to the articulatory loop in verbal memory. An alternative account, which is explored here, is that maintenance is based on shifts of spatial attention. In four experiments, subjects recalled spatial memory span items after an interval, and in a fifth experiment, digit span was recalled after an interval. The tasks carried out during the interval included touching visual targets, repeating heard words, listening to tones from spatially sepa-rated locations, pointing to these tones, pointing to visual targets, and categorizing spatial tar-gets as being from the left or right. Spatial span recall was impaired if subjects saw visual tar-gets or heard tones, and this impairment was increased if either a motor response or a categorical response was made. Repeating words heard in different spatial locations did not impair recall, but reading visually presented words did interfere. For digit span only, the tasks involving a verbal response impaired recall. The results are interpreted within a framework in which active spatial attention is involved in maintaining spatial items in order in memory, and is interfered with by any task (visual, auditory, perceptual, motor) that also makes demands on spatial attention.     

Age, gesture span, and dissociations among component subsystems of working memory

Working memory was examined in old and young adults using a series of span tasks, including the forward versions of the visual-spatial and digit span tasks from the Wechsler Memory Scale-Revised, and comparable hand gesture and visual design span tasks. The observation that the young participants performed significantly better on all the tasks except digit span suggested that aging has an impact on some component subsystems of working memory but not others. Analyses of intercorrelations in span performance supports the dissociation among three component subsystems, one for auditory verbal information (the articulatory loop), one for visual-spatial information (visual-spatial scratch-pad), and one for hand/body postural configuration.     

Maximum key-profile correlation (MKC) as a measure of tonal structure in music

Tonal structure is musical organization on the basis of pitch, in which pitches vary in importance and rate of occurrence according to their relationship to a tonal center. Experiment 1 evaluated the maximum key-profile correlation (MKC), a product of Krumhansl and Schmuckler’s key-finding algorithm (Krumhansl, 1990), as a measure of tonal structure. The MKC is the maximum correlation coefficient between the pitch class distribution in a musical sample and key profiles,which indicate the stability of pitches with respect to particular tonal centers. The MKC values of melodies correlated strongly with listeners’ ratings of tonal structure. To measure the influence of the temporal order of pitches on perceived tonal structure, three measures (fifth span, semitone span, and pitch contour) taken from previous studies of melody perception were also correlated with tonal structure ratings. None of the temporal measures correlated as strongly or as consistently with tonal structure ratings as did the MKC, and nor did combining them with the MKC improve prediction of tonal structure ratings. In Experiment 2, the MKC did not correlate with recognition memory of melodies. However, melodies with very low MKC values were recognized less accurately than melodies with very high MKC values. Although it does not incorporate temporal, rhythmic, or harmonic factors that may influence perceived tonal structure, the MKC can be interpreted as a measure of tonal structure, at least for brief melodies.     

The reliability and stability of verbal working memory measures

The psychometric properties of several commonly used verbal working memory measures were assessed. One hundred thirty-nine individuals in five age groups (18–30, 50–59, 60–69, 70–79, and 80+ years) were tested twice (Time I and Time II) on seven working memory span measures (alphabet span, backward digit span, missing digit span, subtract 2 span, running item span, and sentence span for syntactically simple and complex sentences), with an interval of approximately 6 weeks between testing. There were significant effects of age on all but two of the tasks. All the measures had adequate internal consistency. Correlations between performances at Time I and Time II were significant for all the tasks, other than the missing digit span task. The magnitude of the correlations was similar across the age groups and ranged from .52 to .81. Classification of subjects into discrete memory span groups on the basis of a single measure was highly inconsistent across testing sessions and tasks. Classification into upper and lower quartiles was more stable than using a cutoff score for group membership or than classification into high-, medium-, and low-span groups. Correlational analyses showed that there was a moderate relationship between performances on many of the span tasks. Confirmatory factor analysis suggested that six of the seven tasks reflected a common factor. Both test—retest reliability and stability of classification improved when a composite measure reflecting performance on several tasks was used.     

Stimulus similarity decrements in children's working memory span

Two experiments investigated the impact of the relationship between processing and storage stimuli on the working memory span task performance of children aged 7 and 9 years of age. In Experiment 1, two types of span task were administered (sentence span and operation span), and participants were required to recall either the products of the processing task (sentence-final word, arithmetic total) or a word or digit unrelated to the processing task. Experiment 2 contrasted sentence span and operation span combined with storage of either words or digits, in tasks in which the item to be remembered was not a direct product of the processing task in either condition. In both experiments, memory span was significantly greater when the items to be recalled belonged to a different stimulus category from the material that was processed, so that in sentence span tasks, number recall was superior to word recall, and in operation span tasks, word recall was superior to number recall. Explanations of these findings in terms of similarity-based interference and response competition in working memory are discussed.     

Age and individual differences in working memory: the size judgment span task

The authors introduced the Size Judgment Span (SJS) task, a working memory measure developed for use with persons of varied educational backgrounds and general intellectual ability. The authors pooled data from 5 published articles where the SJS task and other measures of cognitive performance were administered to create an archival data set with 496 participants. Analyses of these data yielded strong evidence of age and individual ability differences in SJS performance, confirming the sensitivity of this task for empirically distinguishing age and ability groups. The SJS was also significantly correlated with the backward digit span and listening span tasks. Using hierarchical regression analyses, the authors examined the SJS task as a predictor of different forms of episodic memory, including spatial location memory, verbal free recall, and recognition memory. Results confirmed the practical utility and predictive validity of the SJS task. The authors considered implications for current theoretical views of working memory.     

The feasibility of working memory tablet tasks in predicting scholastic skills in classroom settings

Cognitive assessment in natural group settings facilitates data collection but poses threats to the validity. In this study, tablet‐based working memory (WM) tasks, the counting span, and reading span were used in predicting 12‐year‐old children's (N = 837) scholastic skills and fluid intelligence in a classroom with environmental noise. WM tasks had excellent internal consistency, correlated with scholastic skills, and accounted for more of the variance in cognitive performance (grade point average, fluid intelligence, scholastic skills) compared with individually administered (n = 190) digit span task. Furthermore, the multilevel analysis revealed that compared with the classrooms with no noise, when naturally occurring speech or nonspeech types of environmental noises were present during assessment, WM scores or the reliability estimates were not lower. In contrast, when both types of noises were present, the relationships between some of the WM and achievement scores were even stronger. Thus, assessments in natural classroom contexts may promote revealing the individual differences in WM.     

Positional Sequences in Two-Choice Discrimination Problems with Non-Positional Cues

Individuals seem to differ in their ability to maintain consistent performance. This is obviously an important attribute of behavior that has been largely neglected by researchers. There is, however, some evidence to suggest that, in certain types of situations, the behaviors of the mental retardate are characterized by a relatively high degree of variability. Two studies are reported here that deal with some of the developmental implications of intraindividual variability. In one study, involving retardates, reliability and generality of response consistency were examined in reaction time, time estimation, and digit span tasks. It was shown that individual differences in consistency are reliable and that these generalize across tasks. A second experiment was concerned with the developmental aspects of variability. First-, third-, and fifth-grade pupils and college students were given many trials on a reaction-time task. A variety of measures, reflecting typical performance, limit of performance, and variability, were computed for each subject. The ability to react quickly shows a developmental trend not only with respect to overall performance, but also in the efficiency with whichthe individual maintains his optimal level of responding.     

Timing the “magical number seven”: Presentation rate and regularity affect verbal working memory performance

The informative value of time and temporal structure often remains neglected in cognitive assessments. However, next to information about stimulus identity we can exploit temporal ordering principles, such as regularity, periodicity, or grouping to generate predictions about the timing of future events. Such predictions may improve cognitive performance by optimising adaptation to dynamic stimuli. Here, we investigated the influence of temporal structure on verbal working memory by assessing immediate recall performance for aurally presented digit sequences (forward digit span) as a function of standard (1000 ms stimulus-onset-asynchronies, SOAs), short (700 ms), long (1300 ms) and mixed (700–1300 ms) stimulus timing during the presentation phase. Participant's digit spans were lower for short and mixed SOA presentation relative to standard SOAs. This confirms an impact of temporal structure on the classic “magical number seven,” suggesting that working memory performance can in part be regulated through the systematic application of temporal ordering principles.