A multiple case study of verbal short-term memory in velo-cardio-facial syndrome

Background Velo‐cardio‐facial syndrome (VCFS, 22q11.2 deletion) is characterized by severely delayed language development. The current study explored the integrity of verbal short‐term memory (STM), a cognitive function critically involved in language development, in eight children with VCFS. Methods Using a multiple case study design, we presented a series of STM tasks exploring immediate serial recall for word and non‐word lists to eight children with VCFS (aged 8–12 years) and to chronological‐age‐matched control groups. A first task assessed the integrity of phonological coding in verbal STM by comparing recall for phonologically similar and dissimilar words. Subsequently, the interaction between verbal knowledge and STM capacity was investigated by comparing recall for high‐ and low‐imageability words, for high‐ and low‐frequency words, and for words and non‐words. A final task assessed short‐term serial order recognition for digit sequences. Results When computing the number of items recalled in the word recall tasks, independently of their serial position, only one child presented consistent difficulties. Short‐term recall of non‐words was normal in each child. Phonological similarity and verbal knowledge influenced STM performance to a similar extent in children with VCFS and controls. On the other hand, when applying a strict serial recall criterion, difficulties with the word and non‐word recall tasks were observed in most children. Half of the patients were also impaired in the serial order recognition task. Conclusions Despite mild intellectual disability, it is possible for short‐term retention capacities for verbal item information to be at an age‐appropriate level in VCFS. However, STM for serial order information could be impaired more specifically.     

A category-specific advantage for numbers in verbal short-term memory: evidence from semantic dementia

This study explored possible reasons for the striking difference between digit span and word span in patients with semantic dementia. Immediate serial recall (ISR) of number and non-number words was examined in four patients. For every case, the recall of single-digit numbers was normal whereas the recall of non-number words was impaired relative to controls. This difference extended to multi-digit numbers, and remained even when frequency, imageability, word length, set size and size of semantic category were matched for the numbers and words. The advantage for number words also applied to the patients' reading performance. Previous studies have suggested that semantic memory plays a critical role in verbal short-term memory (STM) and reading: patients with semantic dementia show superior recall and reading of words that are still relatively well known compared to previously known but now semantically degraded words. Additional assessments suggested that this semantic locus was the basis of the patients' category-specific advantage for numbers. Comprehension was considerably better for number than non-number words. Number knowledge may be relatively preserved in semantic dementia because the cortical atrophy underlying the condition typically spares the areas of the parietal lobes thought to be crucial in numerical cognition but involves the inferolateral temporal-lobes known to support general conceptual knowledge.     

The Role of Semantic Knowledge in Short-term Memory

In this paper we examine the role of stored semantic knowledge in recall from short-term memory. We assessed the performance of a patient (FK), who showed a consistent lack of semantic knowledge for some words (‘unknown’) but not others (‘known’) on a range of serial recall tasks using both spoken and written words. Overall, FK was significantly better at recalling lists of known compared with unknown words. His recall of unknown words was characterized by numerous phonological errors, such as repeating ‘bear skunk’ as ‘bunk scare’. FK showed a relatively normal primacy effect in immediate recall, but a striking lack of a recency effect. This pattern of performance is useful for constraining theoretical accounts of language production and verbal short-term memory and for understanding the role that long-term semantic knowledge may play in maintaining information in short-term memory.     

The role of semantic knowledge in short-term memory

In this paper we examine the role of stored semantic knowledge in recall from short-term memory. We assessed the performance of a patient (FK), who showed a consistent lack of semantic knowledge for some words ('unknown') but not others ('known') on a range of serial recall tasks using both spoken and written words. Overall, FK was significantly better at recalling lists of known compared with unknown words. His recall of unknown words was characterized by numerous phonological errors, such as repeating 'bear skunk' as 'bunk scare'. FK showed a relatively normal primacy effect in immediate recall, but a striking lack of a recency effect. This pattern of performance is useful for constraining theoretical accounts of language production and verbal short-term memory and for understanding the role that long-term semantic knowledge may play in maintaining information in short-term memory.     

A multicomponent exploration of verbal short-term storage deficits in normal aging and Alzheimer's disease

Although many studies have shown diminished performance in verbal short-term memory tasks in normal aging and Alzheimer's disease (AD), the cognitive processes responsible for this verbal short-term storage (STS) impairment are still unclear for both populations. We explored verbal STS functioning in patients with AD, elderly participants, and young participants, by investigating a series of processes that could underlie STS impairments in normal elderly and AD populations. The processes we investigated were (a) the influence of lexical and sublexical language knowledge on short-term storage performance, (b) functioning of the phonological loop component via word length and phonological similarity effects, and (c) executive control processes (coordination and integration). For the AD and elderly groups, the influence of language knowledge on verbal STS performance and the functioning of the phonological loop were preserved. In contrast, the AD group showed deficits for coordination and integration processes. Our results suggest that the verbal STS deficit observed in AD patients is related to impaired executive control processes. On the other hand, language-related processes underlying passive storage capacity seem to be preserved.     

Semantic memory is key to binding phonology: Converging evidence from immediate serial recall in semantic dementia and healthy participants

Patients with semantic dementia (SD) make numerous phoneme migration errors when recalling lists of words they no longer fully understand, suggesting that word meaning makes a critical contribution to phoneme binding in verbal short-term memory. Healthy individuals make errors that appear similar when recalling lists of nonwords, which also lack semantic support. Although previous studies have assumed that the errors in these two groups stem from the same underlying cause, they have never been directly compared. We tackled this issue by examining immediate serial recall for SD patients and controls on “pure” word lists and “mixed” lists that contained a mixture of words and nonwords. SD patients were equally poor at pure and mixed lists and made numerous phoneme migration errors in both conditions. In contrast, controls recalled pure lists better than mixed lists and only produced phoneme migrations for mixed lists. We also examined the claim that semantic activation is critical for words in the primacy portion of the list. In fact, the effect of mixed lists was greatest for later serial positions in the control group and in the SD group recall was poorest towards the ends of lists. These results suggest that mixing nonwords with words in healthy participants closely mimics the impact of semantic degradation in SD on word list recall. The study provides converging evidence for the idea that lexical/semantic knowledge is an important source of constraint on phonological coherence, ensuring that phonemes in familiar words are bound to each other and emerge together in recall.     

Lexicality effects in word and nonword recall of semantic dementia and progressive nonfluent aphasia

Background: Verbal working memory is an essential component of many language functions, including sentence comprehension and word learning. As such, working memory has emerged as a domain of intense research interest both in aphasiology and in the broader field of cognitive neuroscience. The integrity of verbal working memory encoding relies on a fluid interaction between semantic and phonological processes. That is, we encode verbal detail using many cues related to both the sound and meaning of words. Lesion models can provide an effective means of parsing the contributions of phonological or semantic impairment to recall performance.

Methods & Procedures: We employed the lesion model approach here by contrasting the nature of lexicality errors incurred during recall of word and nonword sequences by three individuals with progressive nonfluent aphasia (a phonological dominant impairment) compared to that of two individuals with semantic dementia (a semantic dominant impairment). We focused on psycholinguistic attributes of correctly recalled stimuli relative to those that elicited a lexicality error (i.e., nonword → word OR word → nonword).

Outcomes & Results: Patients with semantic dementia showed greater sensitivity to phonological attributes (e.g., phoneme length, wordlikeness) of the target items relative to semantic attributes (e.g., familiarity). Patients with PNFA showed the opposite pattern, marked by sensitivity to word frequency, age of acquisition, familiarity, and imageability.

Conclusions: We interpret these results in favour of a processing strategy such that in the context of a focal phonological impairment patients revert to an over-reliance on preserved semantic processing abilities. In contrast, a focal semantic impairment forces both reliance on and hypersensitivity to phonological attributes of target words. We relate this interpretation to previous hypotheses about the nature of verbal short-term memory in progressive aphasia.     

Selective effects of cholinergic treatment on verbal memory in posttraumatic amnesia

Abstract

The combined effects or orally administered physostigmine and lecithin were assessed in a double-blind study of a single patient with posttraumatic amnesia. Treatment improved verbal recall but not verbal recognition, visual memory, or conceptual reasoning. Both storage and retrieval of words in verbal memory were facilitated. Greater improvement in learning of longer or semantically homogeneous word lists than shorter or semantically mixed lists may indicate that treatment reduced the effects of interstimulus interference. Greater divergence of recognition response biases for semantically homogeneous vs. mixed lists was observed under treatment, reflecting some enhancement of semantic appreciation. Absence of a treatment effect on visual nonverbal memory may be due in part to lateralization of the mesencephalic lesion to the left in this patient. Lack of improvement of encoding capacity, d', or conceptual reasoning may reflect a greater dependence of basal forebrain structures on catecholaminergic than cholinergic mechanisms.     

How does linguistic knowledge contribute to short-term memory? Contrasting effects of impaired semantic knowledge and executive control

Background: Linguistic knowledge makes an important contribution to verbal STM. Some theories, including Baddeley's original conception of the episodic buffer, hold that harnessing linguistic knowledge to support STM is executively demanding. However, some recent evidence suggests that the linguistic contribution does not depend on executive resources.

Aims: In this study we tested the hypothesis that activation of language representations is automatic and that executive control is most important when the material to be remembered is incompatible with this automatic activation.

Methods & Procedures: Word list recall was tested in three patients with transcortical sensory aphasia (TSA) following stroke. All had preserved word repetition and digit span but poor comprehension associated with impaired executive control. They were compared with two semantic dementia (SD) patients with degraded semantic representations but intact executive control. Patients repeated word lists that varied in their semantic and syntactic resemblance to meaningful sentences.

Outcomes & Results: The executively impaired TSA patients showed large benefits of semantic and syntactic structure, indicating that their executive deficits did not interfere with the normal linguistic contribution to STM. Instead they showed severe deficits in repetition of scrambled word lists that did not follow usual syntactic rules. On these, the patients changed the word order to better fit their existing knowledge of syntactic structure. In contrast, the SD patients had no problems repeating words in unusual sequences but their semantic knowledge degradation led to frequent phonological errors due to a loss of “semantic binding”, the process by which semantic knowledge of words helps to constrain their phonological representation.

Conclusions: These findings suggest that linguistic support for STM consists of (a) automatic activation of semantic and syntactic knowledge and (b) executive processes that inhibit this activation when it is incompatible with the material to be remembered.     

Phonological working memory in children with phonological impairment

Phonological working memory was examined in a group of children with phonological impairment and a group of normal age-matched controls. Based on the Baddeley and Hitch model of working memory, traditional serial recall tasks of word length and phonological similarity were used to examine the efficiency of subvocal rehearsal and short-term storage, respectively. Analysis of recall performance for lists of four and six words revealed that, in comparison to agematched controls, children with phonological impairment are similarly sensitive to the effects of word length and phonological similarity, but demonstrate poorer overall recall for word lists of unrelated items. Theoretically, these findings suggest that the subvocal rehearsal mechanism and the phonological short-term store appear to be operating efficiently in this group of children with phonological impairment. Therefore their poorer recall performance may be attributable to interactions between short-term memory processes and aspects of phonological knowledge stored in long-term memory rather than to specific components of a phonological loop.     

Semantic organization and verbal episodic memory in patients with mild and moderate Alzheimer's disease

The objective of the present research was to investigate the relationship between semantic organization and cue utilization in mildly and moderately demented patients with Alzheimer's disease (AD). In Experiment 1, subjects were presented with two lists of words: a list with semantically unrelated words and a list with words from four semantic categories presented randomly intermixed. Free recall was assessed and following the organizable list, subjects received a cued recall test. Normal controls, as opposed to mildly and moderately demented patients, showed higher performance in the organizable list as compared to the random list. In addition, normal controls and mildly demented patients benefited from semantic cues in the organizable list and performed at a higher level in total recall as compared to free recall. In Experiment 2, subjects were presented with two lists of words: a list with words from four semantic categories presented randomly intermixed and a list with words from four semantic categories presented clustered, together with information about the organization of the list. Free recall and cued recall, with the category names serving as cues, were assessed. Free recall performance of normal controls was higher in the clustered than in the organizable list, whereas no such effect was observed for the AD patients. Normal controls and mildly demented patients performed at a higher level in total as compared to free recall in both lists, whereas this effect was present only in the clustered list for the moderately demented patients. The overall pattern of results indicates that there are conditions under which memory facilitation from semantic organization may be obtained in AD.     

Verbal learning in semantic dementia: Is repetition priming a useful strategy?

Background: Semantic dementia (SD) is a neurodegenerative disease that impacts long-term conceptual and lexical knowledge (Hodges & Patterson, 1996). Severe naming difficulties are prevalent in SD, yet little is known about the potential for word learning in this population.Aims: We assessed patterns of repetition and implicit learning in patients with moderate to advanced SD via repeated exposure to word lists varied by frequency and imageability. We propose a tentative framework for the language loss incurred in SD and open a dialogue for treatment approaches targeted towards progressive semantic anomia.Methods and Procedures: In two experiments, we examined immediate serial recall and short-term learning in five patients with SD. We predicted reduced semantic effects (imageability), preservation of lexical effects (frequency), and diminished primacy effects in serial recall, consistent with other semantically impaired populations (Martin & Saffran, 1997). We also predicted that severity of semantic impairment would modulate the facilitative effects of repeated exposure (i.e., repetition priming) on word list recall.Outcomes and Results: In immediate serial recall, all participants showed reduced imageability effects, but only one patient showed a significant word frequency advantage. Two patterns of serial position effects emerged: (1) poor recall of initial list items and (2) better recall of initial and final items. All participants showed minimal gains across repeated trials; however, patients who poorly recalled initial items showed the least benefit from repeated exposure.Conclusions: We discuss the usefulness of repetition-based interventions for SD and advocate maintenance of known vocabulary over reacquisition of forgotten words. We provide a theoretical framework for progressive language loss associated with SD; this model reflects an ordered reduction of lexical-semantic support coinciding with dementia severity.     

Effects of working memory load on processing of sounds and meanings of words in aphasia

BACKGROUND: Language performance in aphasia can vary depending on several variables such as stimulus characteristics and task demands. This study focuses on the degree of verbal working memory (WM) load inherent in the language task and how this variable affects language performance by individuals with aphasia. AIMS: The first aim was to identify the effects of increased verbal WM load on the performance of judgments of semantic similarity (synonymy) and phonological similarity (rhyming). The second aim was to determine if any of the following abilities could modulate the verbal WM load effect: semantic or phonological access, semantic or phonological short-term memory (STM) and any of the following executive processing abilities: inhibition, verbal WM updating, and set shifting. METHOD AND PROCEDURES: Thirty-one individuals with aphasia and 11 controls participated in this study. They were administered a synonymy judgment task and a rhyming judgment task under high and low verbal WM load conditions that were compared to each other. In a second set of analyses, multiple regression was used to identify which factors (as noted above) modulated the verbal WM load effect. OUTCOME AND RESULTS: For participants with aphasia, increased verbal WM load significantly reduced accuracy of performance on synonymy and rhyming judgments. Better performance in the low verbal WM load conditions was evident even after correcting for chance. The synonymy task included concrete and abstract word triplets. When these were examined separately, the verbal WM load effect was significant for the abstract words, but not the concrete words. The same pattern was observed in the performance of the control participants. Additionally, the second set of analyses revealed that semantic STM and one executive function, inhibition ability, emerged as the strongest predictors of the verbal WM load effect in these judgment tasks for individuals with aphasia. CONCLUSIONS: The results of this study have important implications for diagnosis and treatment of aphasia. As the roles of verbal STM capacity, executive functions and verbal WM load in language processing are better understood, measurements of these variables can be incorporated into our diagnostic protocols. Moreover, if cognitive abilities such as STM and executive functions support language processing and their impairment adversely affects language function, treating them directly in the context of language tasks should translate into improved language function.     

Improved verbal learning in the semantic variant of primary progressive aphasia when using semantic cues

The semantic variant of primary progressive aphasia (PPA-S) is characterized by impairments in confrontation naming and single word comprehension. Although episodic memory may be relatively spared, there can be impairment in verbal learning tasks. We report a patient with PPA-S and impaired verbal learning who was tested to learn if when provided with semantic categories, her learning would improve. A 70-year-old right-handed woman with a 2-year history of progressive difficulties with word finding, naming, and memory was tested for language and memory deficits using the Hopkins Verbal Learning Test-Revised (HVLT-R). She was then retested with the HVLT-R after being provided with the three semantic categories to which these words belonged. Confrontation naming was impaired on the Boston Naming Test. Sentence repetition was normal. Comprehension testing with word picture matching and sentence comprehension was normal. On a test of semantic associations, Pyramids and Palm Trees, she was impaired. She was also impaired on tests of verbal learning (HVLT-R) (total: 13) but not recall. When a different version of the HVLT-R was given with the semantic categories of the words given beforehand, her scores improved (total: 26). This patient with PPA-S had an impairment of verbal learning, but not delayed recall. When given a semantic category cue beforehand, her verbal learning performance improved. This observation suggests that this patient did not spontaneously use semantic encoding. Using a semantic cueing strategy may help other patients with PPA-S improve their capacity for verbal learning.     

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.     

Grouping,semantic relation and imagery effects in individuals with Down syndrome

Down syndrome (DS) is associated with a specific verbal short-term memory (STM) deficit. This study explored the effects of grouping, semantic relations and visual presentation upon verbal STM recall performance in a group of 15 individuals with DS and 15 vocabulary-matched typically developing (TD) children. Participants were presented with memoranda in either a temporally grouped schedule, such that items were grouped as pairs, or in an equally spaced presentation schedule. The two items constituting each pair were either semantically related or unrelated. Performance across these conditions was compared in verbal or verbal plus visual presentation modes. Significant memory recall benefits were observed across populations as a result of temporal grouping, semantic relations and verbal and visual combined presentation. However, a reduced benefit of semantic relation in the DS group compared to the TD group indicated that those with DS were less influenced by LTM relational knowledge. In addition, those with DS only experienced a grouping benefit during verbal and visual combined presentation, in contrast to the TD group who experienced grouping benefits throughout. This indicates that individuals with DS are poorer at encoding temporal context for purely verbal memoranda. These findings were replicated in a follow-up experiment, aimed at aligning baseline performance in the two populations. This study provides encouraging evidence that, despite their difficulties in some areas, individuals with DS can benefit from the use of grouping and LTM knowledge to assist their verbal STM performance under certain circumstances.     

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.     

Processing speed: a strong predictor of verbal memory performance in schizophrenia

The role of slowing of processing speed in verbal memory impairment in patients with schizophrenia was investigated. Forty-one patients with schizophrenia and 41 healthy control subjects were administered a verbal memory task involving free recall of three lists of words, which varied in their degree of semantic organization. Standard processing speed tests were administered as well. Regression analyses were conducted on the number of words recalled in each list. A global processing speed measure was a significant predictor of the recall of each list in patients. Patients were very significantly impaired in the recall of the three lists relative to healthy controls. However, when the processing speed measure was entered in the regression, the significance of diagnosis was considerably reduced for one of the lists, with no semantic organization, and eliminated for the other two lists which contained semantic organization. These findings suggest that slowing in processing speed is an important contributor to verbal memory impairment in patients with schizophrenia. The possible role of various specific slowing functions is discussed.     

Routine clinical diagnosis of primary progressive non-fluent aphasia

It may be difficult to distinguish between a primary progressive aphasia at a very mild stage from the beginning of Alzheimer's disease (AD). However, this may be achieved by carrying out simple neuro-psychological tests. Nine non-fluent PPA (NFPPA) and 76 AD patients with comparable MMSE as well as 58 control subjects were evaluated using simple tests: MMSE, fluency, apraxia, naming, digital span, story memory, 5 words memory test. NFPPA patients had significantly impaired functions during the semantic category fluency and naming tests as compared to AD patients, whereas they showed a better delayed recall of the 5 words and story memory tests. As compared to AD, MMSE of NFPPA patients was also better in the time orientation and word recall sub-tests, although inferior in words repetition and language items. Thus, with comparable MMSE, NFPPA patients have more lexico-semantic difficulties, but a better delayed verbal memory than AD patients. These simple tests easily confirm the language impairment of NFPPA patients as opposed to the mnestic difficulties of AD, even at very early stages of these pathologies.     

Cued recall and release from proactive interference in Alzheimer's disease

Two tasks were administered to 13 mildly to moderately impaired subjects who met clinical research criteria for AD, and 17 controls matched for age and education. In the first task, subjects were administered a cued recall test (Buschke, 1984). AD subjects were found to be variably impaired in their ability to perform the initial stimulus-processing procedure, which involved matching cues with referents. The subsequent cued recall test did not typically facilitate performance. In the second task, subjects were administered a release from proactive interference (PI) paradigm consisting of semantically related and unrelated word lists. AD subjects did not develop the expected proactive interference effect for the semantically related words or show a resulting "release from PI" on related word list recall compared to normal controls. Results are discussed in terms of the role of semantic processing in episodic memory tasks.