Relations between Short-term Memory Deficits, Semantic Processing, and Executive Function

Recovery of Verbal Working Memory Depends on Left Hemisphere White Matter Tracts

Researchers propose that the recovery of language function following stroke depends on the recruitment of perilesional regions in the left hemisphere and/or homologous regions in the right hemisphere (Kiran, 2012). Many investigations of recovery focus on changes in gray matter regions (e.g., Turkeltaub et al., 2011), whereas relatively few examine white matter tracts (e.g., Schlaug et al., 2009) and none address the role of these tracts in the recovery of verbal working memory (WM). The present study addressed these gaps, examining the role of left vs. right hemisphere tracts in the longitudinal recovery of phonological and semantic WM. For 24 individuals with left hemisphere stroke, we assessed WM performance within one week of stroke (acute timepoint) and at more than six months after stroke (chronic timepoint). To address whether recovery depends on the recruitment of left or right hemisphere tracts, we assessed whether changes in WM were related to the integrity of five white matter tracts in the left hemisphere which had been implicated previously in verbal WM and their right hemisphere analogues. Behavioral results showed significant improvement in semantic but not phonological WM from the acute to chronic timepoints. Improvements in semantic WM significantly correlated with tract integrity as measured by functional anisotropy in the left direct segment of the arcuate fasciculus, inferior fronto-occipital fasciculus and inferior longitudinal fasciculus. The results confirm the role of white matter tracts in language recovery and support the involvement of the left rather than right hemisphere in the recovery of semantic WM.

The role of input vs. output phonological working memory in narrative production: Evidence from case series and case study approaches

Separable input and output phonological working memory (WM) capacities have been proposed, with the input capacity supporting speech recognition and the output capacity supporting production. We examined the role of input vs. output phonological WM in narrative production, examining speech rate and pronoun ratio - two measures with prior evidence of a relation to phonological WM. For speech rate, a case series approach with individuals with aphasia found no significant independent contribution of input or output phonological WM capacity after controlling for single-word production. For pronoun ratio, there was some suggestion of a role for input phonological WM. Thus, neither finding supported a specific role for an output phonological buffer in speech production. In contrast, two cases demonstrating dissociations between input and output phonological WM capacities provided suggestive evidence of predicted differences in narrative production, though follow-up research is needed. Implications for case series vs. case study approaches are discussed.

Unraveling the Thread of Aphasia Rehabilitation: A Translational Cognitive Perspective

Translational neuroscience is a multidisciplinary field that aims to bridge the gap between basic science and clinical practice. Regarding aphasia rehabilitation, there are still several unresolved issues related to the neural mechanisms that optimize language treatment. Although there are studies providing indications toward a translational approach to the remediation of acquired language disorders, the incorporation of fundamental neuroplasticity principles into this field is still in progress. From that aspect, in this narrative review, we discuss some key neuroplasticity principles, which have been elucidated through animal studies and which could eventually be applied in the context of aphasia treatment. This translational approach could be further strengthened by the implementation of intervention strategies that incorporate the idea that language is supported by domain-general mechanisms, which highlights the impact of non-linguistic factors in post-stroke language recovery. Here, we highlight that translational research in aphasia has the potential to advance our knowledge of brain-language relationships. We further argue that advances in this field could lead to improvement in the remediation of acquired language disturbances by remodeling the rationale of aphasia-therapy approaches. Arguably, the complex anatomy and phenomenology of aphasia dictate the need for a multidisciplinary approach with one of its main pillars being translational research.

Differential working memory function between phonological and visuospatial strategies: a magnetoencephalography study using a same visual task

Previous studies have reported that, in working memory, the processing of visuospatial information and phonological information have different neural bases. However, in these studies, memory items were presented via different modalities. Therefore, the modality in which the memory items were presented and the strategy for memorizing them were not rigorously distinguished. In the present study, we explored the neural basis of two working memory strategies. Nineteen right-handed young adults memorized seven sequential directions presented visually in a task in which the memory strategy was either visuospatial or phonological (visuospatial/phonological condition). Source amplitudes of theta-band (5-7 Hz) rhythm were estimated from magnetoencephalography during the maintenance period and further analyzed using cluster-based permutation tests. Behavioral results revealed that the accuracy rates showed no significant differences between conditions, while the reaction time in the phonological condition was significantly longer than that in the visuospatial condition. Theta activity in the phonological condition was significantly greater than that in the visuospatial condition, and the cluster in spatio-temporal matrix with p < 5% difference extended to right prefrontal regions in the early maintenance period and right occipito-parietal regions in the late maintenance period. The theta activity results did not indicate strategy-specific neural bases but did reveal the dynamics of executive function required for phonological processing. The functions seemed to move from attention control and inhibition control in the prefrontal region to inhibition of irrelevant information in the occipito-parietal region.

Contributions of semantic and phonological working memory to narrative language independent of single word production: Evidence from acute stroke

ABSTRACTNeuropsychological case studies have provided evidence that individuals with semantic, but not phonological, working memory (WM) deficits have difficulty producing phrases containing several content words. These findings supported the claim of a phrasal scope of planning at the grammatical formulation stage of production, where semantic WM supports the maintenance of lexical-semantic representations as they are inserted into slots in phrasal constituents. Recent narrative production results for individuals at the acute stage of stroke supported the role for semantic WM in phrasal elaboration while suggesting a role for phonological WM at a subsequent phonological encoding stage in supporting fluent, rapid speech. In the present study, we employed a larger participant sample while controlling for single word production abilities at semantic and phonological levels. Results confirmed the relations between semantic WM and phrasal elaboration whereas the relation between phonological WM and speech rate was eliminated. There was, however, evidence that both impaired phonological retrieval and restricted phonological WM were related to the tendency to produce short, highly frequent words such as pronouns rather than longer, less frequent words. Future research is needed to address whether the results relating to phonological WM depend on damage specific to an output rather than an input phonological capacity.

Dissociable language and executive control deficits and recovery in post-stroke aphasia: An exploratory observational and case series study

A growing body of evidence indicates many, but not all, individuals with post-stroke aphasia experience executive dysfunction. Relationships between language and executive function skills are often reported in the literature, but the degree of interdependence between these abilities remains largely unanswered. Therefore, in this study, we investigated the extent to which language and executive control deficits dissociated in 1) acute stroke and 2) longitudinal aphasia recovery. Twenty-three individuals admitted to Johns Hopkins Hospital with a new left hemisphere stroke completed the Western Aphasia Battery-Revised (WAB-R), several additional language measures (of naming, semantics, spontaneous speech, and oral reading), and three non-linguistic cognitive tasks from the NIH Toolbox (i.e., Pattern Comparison Processing Speed Test, Flanker Inhibitory Control and Attention Test, and Dimensional Change Card Sort Test). Two participants with aphasia (PWA) with temporoparietal lesions, one of whom (PWA1) had greater temporal but less frontal and superior parietal damage than the other (PWA2), also completed testing at subacute (three months post-onset) and early chronic (six months post-onset) time points. In aim 1, principal component analysis on the acute test data (excluding the WAB-R) revealed language and non-linguistic executive control tasks largely loaded onto separate components. Both components were significant predictors of acute aphasia severity per the WAB-R Aphasia Quotient (AQ). Crucially, executive dysfunction explained an additional 17% of the variance in AQ beyond the explanatory power of language impairments alone. In aim 2, both case patients exhibited language and executive control deficits at the acute post-stroke stage. A dissociation was observed in longitudinal recovery of these patients. By the early chronic time point, PWA1 exhibited improved (but persistent) deficits in several language domains and recovered executive control. In contrast, PWA2 demonstrated mostly recovered language but persistent executive dysfunction. Greater damage to language and attention networks in these respective patients may explain the observed behavioral patterns. These results demonstrate that language and executive control can dissociate (at least to a degree), but both contribute to early post-stroke presentation of aphasia and likely influence longitudinal aphasia recovery.

Generalizable predictive modeling of semantic processing ability from functional brain connectivity

Semantic processing (SP) is one of the critical abilities of humans for representing and manipulating conceptual and meaningful information. Neuroimaging studies of SP typically collapse data from many subjects, but its neural organization and behavioral performance vary between individuals. It is not yet understood whether and how the individual variabilities in neural network organizations contribute to the individual differences in SP behaviors. We aim to identify the neural signatures underlying SP variabilities by analyzing functional connectivity (FC) patterns based on a large‐sample Human Connectome Project (HCP) dataset and rigorous predictive modeling. We used a two‐stage predictive modeling approach to build an internally cross‐validated model and to test the model's generalizability with unseen data from different HCP samples and other out‐of‐sample datasets. FC patterns within a putative semantic brain network were significantly predictive of individual SP scores summarized from five SP‐related behavioral tests. This cross‐validated model can be used to predict unseen HCP data. The model generalizability was enhanced in the language task compared with other tasks used during scanning and was better for females than males. The model constructed from the HCP dataset can be partially generalized to two independent cohorts that participated in different semantic tasks. FCs connecting to the Perisylvian language network show the most reliable contributions to predictive modeling and the out‐of‐sample generalization. These findings contribute to our understanding of the neural sources of individual differences in SP, which potentially lay the foundation for personalized education for healthy individuals and intervention for SP and language deficits patients.

Intellectual awareness of naming abilities in people with chronic post-stroke aphasia

Anosognosia, or lack of self-awareness, is often present following neurological injury and can result in poor functional outcomes. The specific phenomenon of intellectual awareness, the knowledge that a function is impaired in oneself, has not been widely studied in post-stroke aphasia. We aim to identify behavioral and neural correlates of intellectual awareness by comparing stroke survivors' self-reports of anomia to objective naming performance and examining lesion sites. Fifty-three participants with chronic aphasia without severe comprehension deficits rated their naming ability and completed a battery of behavioral tests. We calculated the reliability and accuracy of participant self-ratings, then examined the relationship of poor intellectual awareness to speech, language, and cognitive measures. We used support vector regression lesion-symptom mapping (SVR-LSM) to determine lesion locations associated with impaired and preserved intellectual awareness. Reliability and accuracy of self-ratings varied across the participants. Poor intellectual awareness was associated with reduced performance on tasks that rely on semantics. Our SVR-LSM results demonstrated that anterior inferior frontal lesions were associated with poor awareness, while mid-superior temporal lesions were associated with preserved awareness. An anterior-posterior gradient was evident in the unthresholded lesion-symptom maps. While many people with chronic aphasia and relatively intact comprehension can accurately and reliably report the severity of their anomia, others overestimate, underestimate, or inconsistently estimate their naming abilities. Clinicians should consider this when administering self-rating scales, particularly when semantic deficits or anterior inferior frontal lesions are present. Administering self-ratings on multiple days may be useful to check the reliability of patient perceptions.

Attention switching deficit in patients of Parkinson's disease who experience freezing of gait

Attention switching is involved in postural adjustments for gait. A deficit in attention switching was expected among patients having Parkinson's disease and experiencing freezing. There was a deficit in attention switching abilities among the patients of Parkinson's disease, having episodes of freezing of gait. The task accuracy and reaction time of the freezing group was significantly reduced compared to the non-freezing group having Parkinson's disease and healthy control group on total AST task performance, congruent and incongruent trials. The non-freezing group with Parkinson's disease was also slower than the healthy control group, but its accuracy was not affected. The results suggest that patients with freezing of gait experienced a stronger deficit in attention-switching than the non-freezing group of Parkinson's disease. This attention switching deficit among freezers may imply inappropriate allocation of attention for postural responses required for stepping and resulting in freezing. Also, the non-freezing group may have prioritized accuracy over time as a compensatory strategy that may be slowing their gait but prevents freezing.

Working Memory Capacities Neurally Dissociate: Evidence from Acute Stroke

Substantial behavioral evidence implies the existence of separable working memory (WM) components for maintaining phonological and semantic information. In contrast, only a few studies have addressed the neural basis of phonological versus semantic WM using functional neuroimaging and none has used a lesion-symptom mapping (LSM) approach. Here, we address this gap, reporting a multivariate LSM study of phonological and semantic WM for 94 individuals at the acute stage of left hemisphere stroke. Testing at the acute stage avoids issues of brain reorganization and the adoption of patient strategies for task performance. The LSM analyses for each WM component controlled for the other WM component and semantic and phonological knowledge at the single word level. For phonological WM, the regions uncovered included the supramarginal gyrus, argued to be the site of phonological storage, and several cortical and subcortical regions plausibly related to inner rehearsal. For semantic WM, inferior frontal regions and the angular gyrus were uncovered. The findings thus provide converging evidence for separable systems for phonological and semantic WM that are distinguished from the systems supporting long-term knowledge representations in those domains.

Evaluating the distinction between semantic knowledge and semantic access: Evidence from semantic dementia and comprehension-impaired stroke aphasia

Theories of semantic memory based on neuropsychological findings have posited a distinction between stored semantic representations and the mechanisms used to access and manipulate them (e.g., Lambon Ralph, Jefferies, Patterson, & Rogers, 2017; Warrington & Cipolotti, 1996). The most recent instantiation of this view, the controlled semantic cognition theory (Lambon Ralph et al., 2017), is supported by findings suggesting that multimodal (i.e., both verbal and nonverbal) semantic deficits may result from qualitatively different impairments: on the one hand, damage to a semantic access mechanism related to executive control, which is observed in semantic aphasia (SA), and on the other, damage to semantic representations, which is observed in semantic dementia (SD) (Jefferies & Lambon Ralph, 2006). In this study we compared SA and SD patients on several phenomena previously used to support these distinctions. Contrary to the prior results, we found that (1) overall, cross-task consistency was equivalent for the two groups; (2) neither patient group showed consistency driven by item identity across different semantic tasks; (3) correlations among task performance were not obviously driven by the semantic control demands of different tasks; (4) both groups showed executive function deficits; and (5) both groups showed strong effects of distractor interference in a synonym judgment task. Furthermore, we investigated the components of executive ability that could underlie semantic control deficits by correlating performance on updating, shifting, and inhibition tasks with performance on tasks testing semantic abilities. We found that updating was related to semantic processing generally, whereas shifting and inhibition were not. These results also suggest that complex executive function tasks relate to semantic tasks through their shared relationship with language abilities. Overall, evidence from SA and SD patients does not differentiate representations and access mechanisms in the semantic system, as has previously been suggested. Implications for the storage-access distinction are discussed.

Performance differences between aphasia and healthy aging on an executive function test battery

Purpose: Executive function (EF) deficits commonly co-occur with other linguistic and non-linguistic deficits in aphasia. The questions about whether, and to what extent, people with aphasia (PWA) present deficits on different executive functions (EFs) is relatively understudied.Method: In this study, four EFs, set-switching, updating, inhibition, and dual task processing were evaluated in aphasia and healthy groups. Three groups of participants: 30 healthy young, 30 healthy old, and 10 PWA were assessed on four tasks, Colour Trails Test (CTT 1 and 2), Conners' Continuous Performance Test II (CPT II), n-back (1- and 2-back), and divided attention task that tapped into different EFs. In order to examine performance differences on the EF tasks between the participant groups, repeated measures and multivariate analysis of variances with follow-up pairwise comparisons were computed. Pearson product-moment correlations were conducted to evaluate the strength and direction of the association between aphasia severity (on Western Aphasia Battery-Revised) and executive functioning.Result: PWA demonstrated significantly diminished performance on all EF tasks in comparison to healthy groups and differences were distinct on the higher-level complexity tasks such as the 2-back and CTT 2. The healthy older group demonstrated elevated response times on the CTT, CPT II, and divided attention tasks, and decreased sensitivity scores on the CPT II and n-back in comparison to the younger group. Also, aphasia severity correlated with reduced performance on selective EF measures.Conclusion: This study emphasises the importance of investigating EF deficits in PWA and its potential relationship to language behaviour. Understanding EF is critical for comprehension of linguistic and non-linguistic deficits and in planning treatment for PWA.

Evaluating the Contribution of Executive Functions to Language Tasks in Cognitively Demanding Contexts

Purpose The purpose of this study was to determine the degree to which the executive functions of attention switching and inhibition predicted performance on language subtests from the Temple Assessment of Language and (Verbal) Short-Term Memory in Aphasia (TALSA; N. Martin, Minkina, Kohen, &Kalinyak-Fliszar, 2018) across 3 interval conditions (no delay, 5-s delay, and 5-s filled delay), which was designed to add a memory and executive load to language tasks. Method This study was a post hoc experimental design. Participants included 27 people with aphasia who were administered 5 subtests from the TALSA (Naming, Word Repetition, Nonword Repetition, Category Judgment, and Rhyming Judgment), which were selected to evaluate input and output levels of processing in the 3 interval conditions listed above. Three executive tasks were administered to evaluate inhibition (Simon and Flanker tasks) and attention switching (number-letter shifting). Results Independent variables were proportion correct on each TALSA task in 3 separate time conditions, and predictor variables were efficiency on the Simon task and number-letter shifting task. Linear regression modeling was completed, which revealed that inhibition was a significant predictor of proportion correct for Word Repetition and Category Judgment in the 5-s filled interval condition. Conclusions Our findings indicate that inhibition plays a role in completing tasks that require lexical and/or semantic processing in cognitively demanding conditions. Attention switching was not a significant predictor for any task. These results are an important step toward creating methods to evaluate executive skills in the context of language production. Supplemental Material https://doi.org/10.23641/asha.9765107.

Maintenance Versus Transmission Deficits: The Effect of Delay on Naming Performance in Aphasia

We propose that deficits in lexical retrieval can involve difficulty in transmission of activation between processing levels, or difficulty in maintaining activation. In support, we present an investigation of picture naming by persons with aphasia in which the naming response is generated after a 1 s (sec) cue to respond in one condition or a 5 s cue to respond in another. Some individuals did better after 5 s, some did worse after 5 s, and some were not impacted by the delay. It is suggested that better performance after 5 s indicates a transmission deficit and that worse performance after 5 s indicates a maintenance deficit. To support this hypothesis, we adapted the two-step semantic-phonological model of lexical retrieval (Schwartz et al., 2006) so that it can simulate the passage of time and can simulate lesions in transmission (its semantic and phonological connection strength parameters) and/or maintenance (its decay parameter). The naming error patterns after 1 and 5 s for each participant were successfully fit to the model. Persons who did better after 5 s were found to have low connection strength parameters, persons who did worse after 5 s were simulated with an increased decay rate, and persons whose performance did not differ with delay were found to have lesions of both types. Some potential theoretical and clinical implications are discussed.

Effects of Verb Overlap on Structural Priming in Dialogue: Implications for Syntactic Learning in Aphasia

Purpose Although there is increasing interest in using structural priming as a means to ameliorate grammatical encoding deficits in persons with aphasia (PWAs), little is known about the precise mechanisms of structural priming that are associated with robust and enduring effects in PWAs. Two dialogue-like comprehension-to-production priming experiments investigated whether lexically independent (abstract structural) priming and/or lexically (verb) specific priming yields immediate and longer, lasting facilitation of syntactic production in PWAs. Method Seventeen PWAs and 20 healthy older adults participated in a collaborative picture-matching task where participant and experimenter took turns describing picture cards using transitive and dative sentences. In Experiment 1, a target was elicited immediately following a prime. In Experiment 2, 2 unrelated utterances intervened between a prime and target, thereby allowing us to examine lasting priming effects. In both experiments, the verb was repeated for half of the prime-target pairs to examine the lexical (verb) boost on priming. Results Healthy older adults demonstrated abstract priming in both transitives and datives not only in the immediate (Experiment 1) but also in the lasting (Experiment 2) priming condition. They also showed significantly enhanced priming by verb overlap (lexical boost) in transitives during immediate priming. PWAs demonstrated abstract priming in transitives in both immediate and lasting priming conditions. However, the magnitude of priming was not enhanced by verb overlap. Conclusions Abstract structural priming, but not lexically specific priming, is associated with reliable and lasting facilitation of message-structure mapping in aphasia. The findings also suggest that implicit syntactic learning via a dialogue-like comprehension-to-production task remains preserved in aphasia.

The role of executive control in post-stroke aphasia treatment

Executive control (EC) ability is increasingly emerging as an important predictor of post-stroke aphasia recovery. This study examined whether EC predicted immediate treatment gains, treatment maintenance and generalization after naming therapy in ten adults with mild to severe chronic post-stroke aphasia. Performance on multiple EC tasks allowed for the creation of composite scores for common EC, and the EC processes of shifting, inhibition and working memory (WM) updating. Participants were treated three times a week for five weeks with a phonological naming therapy; difference scores in naming accuracy of treated and untreated words (assessed pre, post, four- and eight-weeks after therapy) served as the primary outcome measures. Results from simple and multiple linear regressions indicate that individuals with better shifting and WM updating abilities demonstrated better maintenance of treated words at four-week follow-up, and those with better common EC demonstrated better maintenance of treated words at both four- and eight-week follow-ups. Better shifting ability also predicted better generalization to untreated words post-therapy. Measures of EC were not indicative of improvements on treated words immediately post-treatment, nor of generalization to untreated words at follow-up. Findings suggest that immediate treatment gains, maintenance and generalization may be supported by different underlying mechanisms.

The dual origin of semantic errors in access deficit: activation vs. inhibition deficit

According to most models of language production, to name a picture one must first map semantic features onto lexical items. Even if both sets of representations are intact, problems in mapping semantic to lexical representations can impair production. Individuals with this problem, sometimes referred to as "access deficit", often demonstrate evidence of preserved semantic knowledge (e.g., good comprehension), increased rate of lexical (usually semantic) errors in production, and inconsistent accuracy on naming the same picture on different occasions. In this paper, I argue that access deficit can have two distinct etiologies. I will present a case of double dissociation between two individuals with chronic post-stroke aphasia, one of whom shows a profile compatible with impaired activation of the target lexical item from semantic features (activation deficit), while the other shows a profile compatible with impaired inhibition of competing lexical items (inhibition deficit). These results have three key implications: (a) they provide support for the theoretical separation between activation and selection processes in computational models of word production, (b) they point to the critical role of inhibitory control in lexical selection, and (c) they invite a closer inspection of the origin of semantic errors in individuals with access deficit in order to choose the best treatment option.

A new index of semantic short-term memory: Development and validation of the conceptual span task in Spanish

Mounting evidence from both cognitive and neuropsychological research points to the importance of conceptual and lexical-semantic contributors to short-term memory performance. Nonetheless, a standardized and well-controlled measure to assess semantic short-term memory was only recently developed for English-speakers, and no parallel measure exists for Spanish-speakers. In the conceptual replication and extension reported here, we develop and validate a Spanish adaptation of the Conceptual Span task as a tool to measure the semantic component of short-term memory. Two versions of the task were validated, the Clustered and the Non-Clustered Conceptual Span task, both in separate samples of 64 and 105 Spanish-speaking university students. We found that both versions of the Conceptual Span task correlate well with another widely used standardized measure of working memory capacity, the Reading Span task. The two versions also correlated, as expected, with discrimination of linguistic congruency as assessed by a semantic anomaly judgment task. Clustered Conceptual Span remained a significant predictor of Reading Span when controlling for several additional cognitive variables, including fluid reasoning, text comprehension, verbal fluency, ideational fluency, and speed of processing. Our results present evidence that the Spanish adaptation of both versions of the Conceptual Span task can yield reliable estimates of the active maintenance of semantic representations in verbal working memory–an under-investigated ability that is involved in diverse domains such as episodic memory retrieval, language processing, and comprehension. Thus, the Conceptual Span task validated here can be employed to predict individual variation in semantic short-term memory capacity in a broad range of research domains.

Independent contributions of semantic and phonological working memory to spontaneous speech in acute stroke

Patients with left hemisphere stroke often have language deficits which impair their ability to produce phrases and sentences. One possible source of these speech impairments is the disruption of verbal working memory (WM). Single-case studies of chronic stroke have suggested the existence of a WM capacity specific to maintaining semantic information that is critical for preparing multiple words in phrases prior to speech onset (Freedman, Martin, & Biegler, 2004; Martin & Freedman, 2001; Martin & He, 2004; Martin, Miller, & Vu, 2004). The current study tested this hypothesis by examining spontaneous narrative language production and working memory capacities in a large sample of individuals at the acute stage of stroke (N = 36), prior to the reorganization of function or strategy development. Here we show using a multiple regression approach that patients' semantic but not phonological WM capacity had an independent contribution in predicting phrasal elaboration and increasing utterance length whereas patients' phonological but not semantic WM capacity had an independent contribution in predicting a more rapid speech rate. Importantly, neither WM capacity independently predicted grammatical abilities in speech, implying that the other relations did not result from overall severity. These results indicate that separable semantic and phonological WM components exist that support different aspects of narrative speech. To our knowledge, this is the first study to examine spontaneous speech in a large group of acute stroke patients demonstrating a critical relationship between working memory and the ability to produce more words in phrases and longer utterances.

Short-term memory span in aphasia: Insights from speech-timing measures

Auditory-verbal short-term memory impairments are part and parcel of aphasia and interfere with linguistic processing. To date, the science about short-term memory impairments in aphasia has been generated and dominated by studying measures of accuracy, that is, span length. Because accuracy is expressed through speech, examining the speech-timing characteristics of persons with aphasia as they engage in spoken recall could reveal insights about the manner in which accuracy is achieved. Six speech-timing measures (e.g., response durations, pause durations) were elicited from the speech waveform of word span tasks from twelve people with aphasia. Speech-timing measures were compared to neuro-typical control participants. Speech-timing performance between erroneous and correct responses in the aphasia group was also examined. Across all measures, people with aphasia produced considerably longer speech-timing patterns in comparison to control participants. Memory load affected some measures in people with aphasia and control participants. Speech-timing in correct response trials was shorter than responses in erroneous trials. Memory span correlated only with one measure, namely, speech time (defined as the sum of each individual word duration in a response). Speech time also correlated with the following measures: Aphasia severity (Aphasia Quotient of the Western Aphasia Battery), spontaneous speech, and language comprehension (also measured by the Western Aphasia Battery). Some protracted speech-timing patterns in the aphasia group may be explained by a deregulation of activation-decay patterns. However, in the absence of further evidence from people with aphasia, possible issues around the sensitivity of some speech-timing measures limit firmer conclusions. Speech-timing measures are response-time measures, which have not been systematically studied in studies of short-term or working memory in aphasia and as such, can push the current boundaries of knowledge of short-term and working memory impairments in aphasia, not only in stroke related aphasia but also other neurological conditions.

An individual differences approach to semantic cognition: Divergent effects of age on representation, retrieval and selection

Semantic cognition refers to the appropriate use of acquired knowledge about the world. This requires representation of knowledge as well as control processes which ensure that currently-relevant aspects of knowledge are retrieved and selected. Although these abilities can be impaired selectively following brain damage, the relationship between them in healthy individuals is unclear. It is also commonly assumed that semantic cognition is preserved in later life, because older people have greater reserves of knowledge. However, this claim overlooks the possibility of decline in semantic control processes. Here, semantic cognition was assessed in 100 young and older adults. Despite having a broader knowledge base, older people showed specific impairments in semantic control, performing more poorly than young people when selecting among competing semantic representations. Conversely, they showed preserved controlled retrieval of less salient information from the semantic store. Breadth of semantic knowledge was positively correlated with controlled retrieval but was unrelated to semantic selection ability, which was instead correlated with non-semantic executive function. These findings indicate that three distinct elements contribute to semantic cognition: semantic representations that accumulate throughout the lifespan, processes for controlled retrieval of less salient semantic information, which appear age-invariant, and mechanisms for selecting task-relevant aspects of semantic knowledge, which decline with age and may relate more closely to domain-general executive control.

Verbal short-term memory capacities and executive function in semantic and syntactic interference resolution during sentence comprehension: Evidence from aphasia

This study examined the role of verbal short-term memory (STM) and executive function (EF) underlying semantic and syntactic interference resolution during sentence comprehension for persons with aphasia (PWA) with varying degrees of STM and EF deficits. Semantic interference was manipulated by varying the semantic plausibility of the intervening NP as subject of the verb and syntactic interference was manipulated by varying whether the NP was another subject or an object. Nine PWA were assessed on sentence reading times and on comprehension question performance. PWA showed exaggerated semantic and syntactic interference effects relative to healthy age-matched control subjects. Importantly, correlational analyses showed that while answering comprehension questions, PWA' semantic STM capacity related to their ability to resolve semantic but not syntactic interference. In contrast, PWA' EF abilities related to their ability to resolve syntactic but not semantic interference. Phonological STM deficits were not related to the ability to resolve either type of interference. The results for semantic interference are consistent with prior findings indicating a role for semantic but not phonological STM in sentence comprehension, specifically with regard to maintaining semantic information prior to integration. The results for syntactic interference are consistent with the recent findings suggesting that EF is critical for syntactic processing.

The use of standardised short-term and working memory tests in aphasia research: a systematic review

Impairments of short-term and working memory (STM, WM), both verbal and non-verbal, are ubiquitous in aphasia. Increasing interest in assessing STM and WM in aphasia research and clinical practice as well as a growing evidence base of STM/WM treatments for aphasia warrant an understanding of the range of standardised STM/WM measures that have been utilised in aphasia. To date, however, no previous systematic review has focused on aphasia. Accordingly, the goals of this systematic review were: (1) to identify standardised tests of STM and WM utilised in the aphasia literature, (2) to evaluate critically the psychometric strength of these tests, and (3) to appraise critically the quality of the investigations utilising these tests. Results revealed that a very limited number of standardised tests, in the verbal and non-verbal domains, had robust psychometric properties. Standardisation samples to elicit normative data were often small, and most measures exhibited poor validity and reliability properties. Studies using these tests inconsistently documented demographic and aphasia variables essential to interpreting STM/WM test outcomes. In light of these findings, recommendations are provided to foster, in the future, consistency across aphasia studies and confidence in STM/WM tests as assessment and treatment outcome measures.

Changes in the default mode networks of individuals with long-term unilateral sensorineural hearing loss

Hearing impairment contributes to cognitive dysfunction. Previous studies have found changes of functional connectivity in the default mode network (DMN) associated with cognitive processing in individuals with sensorineural hearing loss (SNHL). Whereas the changes in the DMN in patients with long-term unilateral SNHL (USNHL) is still not entirely clear. In this work, we analyzed resting-state functional magnetic resonance imaging (fMRI) data and neuropsychological test scores from normal hearing subjects (n = 11) and patients (n = 21) with long-term USNHL. Functional connectivity and nodal topological properties were computed for every brain region in the DMN. Analysis of covariance (ANCOVA) and post hoc analyses were conducted to identify differences between normal controls and patients for each measure. Results indicated that the left USNHL presented enhanced connectivity (p < 0.05, false discovery rate (FDR) corrected), and significant changes (p < 0.05, Bonferroni corrected) of the nodal topological properties in the DMN compared with the control. More changes in the DMN have been found in the left than right long-term USNHL (RUSNHL). However, the neuropsychological tests did not show significant differences between the USNHL and the control. These findings suggest that long-term USNHL contributes to changes in the DMN, and these changes might affect cognitive abilities in patients with long-term USNHL. Left hearing loss affects the DMN more than the right hearing loss does. The fMRI measures might be more sensitive for observing cognitive changes in patients with hearing loss than clinical neuropsychological tests. This study provides some insights into the mechanisms of the association between hearing loss and cognitive function.

Working memory and planning during sentence production

Speakers retrieve conceptual, syntactic and lexical information in advance of articulation during sentence production. What type of working memory (WM) store is used to hold the planned information before speaking? To address this question, we measured onset latencies when subjects produced sentences that began with either a complex or a simple initial noun phrase, while holding semantic, phonological or spatial information in WM. Although we found that subjects had longer onset latencies for sentences beginning with a complex noun phrase, showing a phrasal scope of planning, the magnitude of this complexity effect was not affected by any type of WM load. However, subjects made more syntactic errors (but not lexical errors) for sentences beginning with a complex noun phrase, suggesting that advance planning for these phrases occurs at a syntactic rather than lexical-semantic level, which may account for the lack of effect with various types of WM load in the current study.

Active maintenance of semantic representations

In research on verbal working memory, articulatory rehearsal, a maintenance mechanism for phonological representations, has undergone intensive and excellent study. Possible mechanisms for semantic representation have received less attention. However, several studies have reported a double dissociation in types of memory deficits (semantic memory difficulties vs. phonological memory difficulties). This suggests the separability of two maintenance mechanisms. The present study focused on this separability in individuals with normal memory abilities, using a dual-task interference paradigm. The results indicate a crossover interaction between memory and interference task effects: Preventing articulatory rehearsal more strongly disrupted the phonological memory task, whereas performing a tapping task that interfered with attentional control more strongly disrupted semantic memory. These results suggest that semantic representations are actively maintained by a mechanism other than phonological maintenance.

Accent identification by adults with aphasia

The UK is a diverse society where individuals regularly interact with speakers with different accents. Whilst there is a growing body of research on the impact of speaker accent on comprehension in people with aphasia, there is none which explores their ability to identify accents. This study investigated the ability of this group to identify the geographical origins of a speaker. Age-matched participants with and without aphasia listened to 120 audio recordings of five speakers each of six accents, reading aloud four sentences each. Listeners were asked to make a forced-choice decision about the geographical origin of the speaker. Adults with aphasia were significantly less accurate than control participants at identifying accents but both groups made the same pattern of errors. Adults with aphasia who are able to identify a new speaker as being from a particular place may draw on this information to help them "tune in" to the accent.