Verbal working memory deficit in Parkinson's disease subjects.

The aim of the present work was to evaluate verbal working memory in patients affected by Parkinson's disease (PD). In particular, tests that explore the functionality of the Articulatory Loop and of the Central Executive during verbal tasks were given. PD patients displayed normal phonological similarity, word length and word frequency effects in a Word span task, thus demonstrating adequate retention capacity of the phonological store, normal functioning of the articulatory rehearsal mechanism and a normal contribution of lexical-semantic knowledge to verbal immediate recall. In the Brown-Peterson task, PD patients showed abnormal performance decay on the letter recall task when articulatory rehearsal was inhibited by a serial subtraction concurrent task. These data provide evidence for normal functioning of the Articulatory Loop in PD patients. However, when the verbal recall task is more attention demanding, PD patients show deficient performance levels, presumably due to depleted processing resources by the Central Executive.     

Verbal short‐term memory in Down's syndrome: An articulatory loop deficit?

Background Verbal short‐term memory, as measured by digit or word span, is generally impaired in individuals with Down's syndrome (DS) compared to mental age‐matched controls. Moving from the working memory model, the present authors investigated the hypothesis that impairment in some of the articulatory loop sub‐components is at the base of the deficient maintenance and recall of phonological representations in individuals with DS. Methods Two experiments were carried out in a group of adolescents with DS and in typically developing children matched for mental age. In the first experiment, the authors explored the reliance of these subjects on the subvocal rehearsal mechanism during a word‐span task and the effects produced by varying the frequency of occurrence of the words on the extension of the word span. In the second experiment, they investigated the functioning of the phonological store component of the articulatory loop in more detail. Results A reduced verbal span in DS was confirmed. Neither individuals with DS nor controls engaged in spontaneous subvocal rehearsal. Moreover, the data provide little support for defective functioning of the phonological store in DS. Conclusions No evidence was found suggesting that a dysfunction of the articulatory loop and lexical‐semantic competence significantly contributed to verbal span reduction in subjects with DS. Alternative explanations of defective verbal short‐term memory in DS, such as a central executive system impairment, must be considered.     

Executive dysfunction in patients with spinocerebellar ataxia type 3

The aim of this study was to assess the cognitive functions of patients with spinocerebellar ataxia type 3(SCA3). We examined 15 patients with genetically confirmed SCA3 and 15 healthy control subjects matched for age, years of education, and intellectual ability. We administered verbal memory (word recall and word recognition) and executive function tasks (word fluency test, forward and backward digit and visual span tests, Kana Pick-out Test, Trail Making Test, and conflicting instructions and a Go/NoGo task from the Frontal Assessment Battery). We found that patients with SCA3 had significantly lower scores than the healthy control subjects on the word recall, semantic, and letter fluency, and backward digit span tests, while word recognition was well preserved. The other executive function tests showed preserved functions in the SCA3 group, indicating that visual working memory, and attention and inhibition control were not affected. The patients with SCA3 showed impaired word recall and intact word recognition, and accordingly, episodic memory encoding and storage processes in short-term memory were preserved. In category and letter-fluency tests, impairment was attributable to word-retrieval from semantic memory. Impaired verbal working memory may be involved in the retrieval of verbal information from phonological storage by means of continuous subvocal rehearsal, rather than a deficit in initial phonological encoding. Essential executive dysfunction in patients with SCA3 may be due to damage in the cerebellar cortex–ventral dentate nucleus–thalamus–prefrontal cortex circuits, which are involved in strategic retrieval of verbal information from different modes of memory storage.     

A stroke patient with impairment of auditory sensory (echoic) memory

A 42-year-old man suffered damage to the left supra-sylvian areas due to a stroke and presented with verbal short-term memory (STM) deficits. He occasionally could not recall even a single syllable that he had heard one second before. A study of mismatch negativity using magnetoencephalography suggested that the duration of auditory sensory (echoic) memory traces was reduced on the affected side of the brain. His maximum digit span was four with auditory presentation (equivalent to the 1st percentile for normal subjects), whereas it was up to six with visual presentation (almost within the normal range). He simply showed partial recall in the digit span task, and there was no self correction or incorrect reproduction. From these findings, reduced echoic memory was thought to have affected his verbal short-term retention. Thus, the impairment of verbal short-term memory observed in this patient was “pure auditory” unlike previously reported patients with deficits of the phonological short-term store (STS), which is the next higher-order memory system. We report this case to present physiological and behavioral data suggesting impaired short-term storage of verbal information, and to demonstrate the influence of deterioration of echoic memory on verbal STM.     

Phonological recoding, visual short-term store and the effect of unattended speech: evidence from a case of slowly progressive anarthria

Phonological processing and short-term memory were investigated in a patient with slowly progressive anarthria. The patient, who had an auditory-verbal span in the lower unimpaired range, showed preserved phonological similarity and word length effects with auditory presentation. These phonological effects of immediate retention were absent with visual input. The patient was also unable to perform phonological judgments on written verbal material. Under unattended speech interference her visual span improved, with an increase of visual confusion errors. In the light of a model including a main auditory-verbal storage component (the phonological short-term input store, STS), and a rehearsal process, that, after phonological recoding, conveys visually presented verbal material to the phonological STS, the patient's pattern of impairment is interpreted as a selective deficit in the process of phonological recoding. This prevents visual-verbal material from accessing the phonological STS, that is, therefore, insulated from visual inputs.     

The neural correlates of phonological short-term memory: a repetitive transcranial magnetic stimulation study

Neuropsychological reports and activation studies by means of positron emission tomography and functional magnetic resonance imaging have suggested that the neural correlates of phonological short-term memory are located in the left hemisphere, with Brodmann's area (BA) 40 being responsible for short-term storage, and BA 44 for articulatory rehearsal. However, a careful review of the literature on the role of left BA 40 shows that the data are equivocal. We tested these hypotheses by means of repetitive transcranial magnetic stimulation (rTMS). Participants performed four tasks: two phonological judgements, thought to require only articulatory rehearsal without the contribution of short-term storage; a digit span, which involves both, short-term storage and articulatory rehearsal; and a pattern span, this last being the control task. The sites of stimulation were left BA 40, left BA 44 and the electrode location v(tx), plus a baseline without TMS. Reaction times increased and accuracy decreased in the case of the phonological judgements and digit span after stimulation of both left sites, suggesting that BA 40, in addition to BA 44, is involved in phonological judgements. Possible explanations are discussed, namely, the possibility that (i) the neural correlates of rehearsal are not limited to BA 44 and (ii) phonological judgements involve processes other than rehearsal. We also consider the effects of using different tasks and responses to resolve some of the discrepancies in the literature.     

Down syndrome and the phonological loop: the evidence for, and importance of, a specific verbal short-term memory deficit

Individuals with Down syndrome are thought to perform poorly on tests of verbal short-term memory, such as measures of word span or digit span. This review critically examines the evidence for a specific deficit in verbal short-term memory in Down syndrome, and outlines a range of possible explanations for such a deficit. The potential implications of a verbal short-term memory impairment for broader aspects of development are outlined, in particular with respect to vocabulary development. Possible intervention strategies, which might improve verbal short-term memory performance in Down syndrome are also considered. However, we argue that further research is needed to fully clarify the nature of a verbal short-term memory deficit in Down syndrome, before the merits of these various intervention approaches can be properly evaluated.     

Verbal short-term memory in individuals with congenital articulatory disorders: new empirical data and review of the literature

Background To investigate the nature of the articulatory rehearsal mechanism of the Articulatory Loop in Baddeley's Working Memory model, it seems particularly important to study individuals who developed a deficit (dysarthria) or total abolition (anarthria) of the ability to articulate language following a cerebral lesion. Method In this study, a forced‐choice recognition procedure for word sequences of increasing length was used to evaluate verbal short‐term memory in nine individuals with severe congenital motor and verbal disabilities (seven anarthric and two severely dysarthric) and associated intellectual disability (ID) and 30 normal children of comparable mental age. Results The normal children exhibited classical phonological similarity effects (better performance on acoustically dissimilar than on similar word lists), word length (greater accuracy on two‐syllable than on four‐syllable word lists) and frequency of occurrence (an advantage of high‐frequency over low‐frequency words). Instead, all of these effects were lacking in the experimental group. Conclusions These data suggest that persons with congenital anarthria/dysarthria and ID present defective maturation at many levels of the Articulatory Loop and reduced contribution of semantic‐lexical processing in the temporary retention of phonological sequences. It is likely that in these individuals both communicative deficits and ID play a role in the impaired development of verbal short‐term memory abilities.     

Cognitive consequences of early phase of literacy.

The effect of the degree of illiteracy (complete or incomplete) on phonological skills, verbal and visual memory and visuospatial skills is examined in 97 normal Brazilian adults who considered themselves illiterate, and 41 Brazilian school children aged 7 to 8 years, either nonreaders or beginning readers. Similar literacy effects were observed in children and in adults. Tasks involving phonological awareness and visual recognition memory of nonsense figures distinguish the best nonreaders and beginning readers. Children performed better than adults at oral repetition of short items and figure recall, and adults better than children at semantic verbal fluency, digit span, and word list recall. A principal component analysis of the correlations between tasks showed that phonological awareness/reading, phonological memory/oral repetition, and semantic verbal memory/fluency tasks, generated different components. The respective role of culturally based preschool activities and literacy on the cognitive functions that are explored in this study is discussed.     

The hand movement test as a tool in neuropsychological assessment: interpretation within a working memory theoretical framework.

While the Kaufman Hand Movements Test (KHMT) is argued to be sensitive to cognitive impairment secondary to various forms of brain dysfunction in adults, it is unknown which cognitive processes it addresses. Dual-task research has employed tasks similar to the KHMT to determine whether such tasks assess (1) verbal or visuospatial memory, or (2) a proposed additional short-term memory component, movement memory. However findings consistent with both hypotheses have been reported. Experiment 1 involved 24 participants completing a hand movement task and a letter span task under articulatory suppression, finger movement and no interference conditions. Performance on both the hand movement task and letter span task was significantly reduced by articulatory suppression. In Experiment 2, 16 participants were administered the hand movement task and a Corsi span task under articulatory suppression, finger movement, spatial tapping, and no interference. Again, hand movement span was most reduced by articulatory suppression, in contrast to Corsi span which was most reduced by spatial tapping. Hand movement task performance was therefore assumed to rely upon verbal recoding strategies and thus the proposition of an additional component of movement memory was not supported.