Sharon M. Antonucci

Lexical retrieval and semantic knowledge in patients with left inferior temporal lobe lesions.

Background: It has been proposed that anomia following left inferior temporal lobe lesions may have two different underlying mechanisms with distinct neural substrates. Specifically, naming impairment following damage to more posterior regions (BA 37) has been considered to result from a disconnection between preserved semantic knowledge and phonological word forms (pure anomia), whereas anomia following damage to anterior temporal regions (BAs 38, 20/21) has been attributed to the degradation of semantic representations (semantic anomia). However, the integrity of semantic knowledge in patients with pure anomia has not been demonstrated convincingly, nor were lesions in these cases necessarily confined to BA 37. Furthermore, evidence of semantic anomia often comes from individuals with bilateral temporal lobe damage, so it is unclear whether unilateral temporal lobe lesions are sufficient to produce significant semantic impairment. This research was supported by a Graduate Imaging Fellowship from the University of Arizona and by NIH grants RO1DC008286 and RO1DC07464. Scans were funded through Arizona Alzheimers Research Consortium, Cognition and NeuroImaging Lab, Arizona Department of Health Services HB2354. Many thanks to Jen Parrott, Kristin Boruff, and Cathy West for their time and assistance. The authors thank Mark Borgstrom, statistical consultant at the University of Arizona, for his assistance with this project. We also thank Chris Rorden for advice regarding lesion analyses. Aims: The main goals of this study were to determine whether anomia following unilateral left inferior temporal lobe damage reflected a loss of semantic knowledge or a post‐semantic deficit in lexical retrieval and to identify the neuroanatomical correlates of the naming impairment. Methods & Procedures: Eight individuals who underwent left anterior temporal lobectomy (L ATL) and eight individuals who sustained left posterior cerebral artery strokes (L PCA) completed a battery of language measures that assessed lexical retrieval and semantic processing, and 16 age‐ and education‐matched controls also completed this battery. High‐resolution structural brain scans were collected to conduct lesion analyses. Outcomes & Results: Performance of L ATL and L PCA patients was strikingly similar, with both groups demonstrating naming performance ranging from moderately impaired to unimpaired. Anomia in both groups occurred in the context of mild deficits to semantic knowledge, which manifested primarily as greater difficulty in naming living things than nonliving things and greater difficulty in processing visual/perceptual as opposed to functional/associative semantic attributes. Lesion analyses indicated that both patient groups sustained damage to anterior inferior temporal lobe regions implicated in semantic processing. Conclusions: These results contribute to a better understanding of the cognitive mechanism of naming impairment in patients with temporal lobe damage and support the notion that pure anomia and semantic anomia represent two endpoints along a continuum of semantic impairment. Unilateral left temporal lobe lesions in our patients resulted in relatively mild semantic deficits that were apparent primarily in lexical production tasks, whereas severe semantic impairment likely requires bilateral temporal lobe damage.

Use of semantic feature analysis in group aphasia treatment

Background: Semantic feature analysis (SFA) is a treatment for lexical retrieval impairment in which participants are cued to provide semantic information about concepts they have difficulty naming in an effort to facilitate accurate lexical retrieval (Boyle, 2004b). The majority of studies of SFA have concentrated on single‐word training, with inconsistent generalisation of improved lexical retrieval to connected speech. Expansion of SFA training in discourse has yielded modest success in the context of individual treatment, but has not been examined in the context of group treatment. Aims: The aim of the current study was to investigate training of SFA in connected speech during group aphasia treatment, which provides a natural context for analysing the effectiveness of discourse production, as well as representing an increasingly popular model of service delivery for aphasia treatment. It was hypothesised that lexical retrieval during discourse would improve, as would overall communication informativeness. Methods & Procedures: Three individuals with aphasia participated in biweekly group treatment during which SFA was trained during discourse production tasks. Two of the three individuals participated in the entire course of treatment. Discourse of these two participants was analysed such that effect sizes could be calculated for measures of overall communication informativeness and efficiency (Nicholas & Brookshire, 1993), and for item‐specific lexical retrieval (Mayer & Murray, 2003). Outcomes & Results: The two individuals who participated in the full treatment protocol both demonstrated improved lexical retrieval in discourse, with additional improvements observed in either general communication informativeness or efficiency. Conclusions: Results provide preliminary support for the hypotheses that SFA administered during group aphasia treatment can be used successfully to facilitate word retrieval during discourse. Furthermore, results suggest that individuals with differing mechanisms of anomia may derive benefits from participation in this treatment protocol.

Anomia as a Marker of Distinct Semantic Memory Impairments in Alzheimer's Disease and Semantic Dementia

OBJECTIVE Many neurologically constrained models of semantic memory have been informed by two primary temporal lobe pathologies: Alzheimers disease (AD) and Semantic Dementia (SD). However, controversy persists regarding the nature of the semantic impairment associated with these patient populations. Some argue that AD presents as a disconnection syndrome in which linguistic impairment reflects difficulties in lexical or perceptual means of semantic access. In contrast, there is a wider consensus that SD reflects loss of core knowledge that underlies word and object meaning. Object naming provides a window into the integrity of semantic knowledge in these two populations. METHOD We examined naming accuracy, errors and the correlation of naming ability with neuropsychological measures (semantic ability, executive functioning, and working memory) in a large sample of patients with AD (n = 36) and SD (n = 21). RESULTS Naming ability and naming errors differed between groups, as did neuropsychological predictors of naming ability. Despite a similar extent of baseline cognitive impairment, SD patients were more anomic than AD patients. CONCLUSIONS These results add to a growing body of literature supporting a dual impairment to semantic content and active semantic processing in AD, and confirm the fundamental deficit in semantic content in SD. We interpret these findings as supporting of a model of semantic memory premised upon dynamic interactivity between the process and content of conceptual knowledge.

Use of semantic feature analysis in group discourse treatment for aphasia: Extension and expansion

Background: Semantic feature analysis (SFA) is a treatment for lexical retrieval impairment in which participants are cued to provide semantic information about concepts they have difficulty naming, in an effort to facilitate accurate lexical retrieval (Boyle, 2004a). Previous work has provided preliminary evidence that persons with aphasia who participated in SFA-focused group aphasia treatment demonstrate improved lexical retrieval in discourse, with additional improvements observed in either general communication informativeness or efficiency (Antonucci, 2009). Furthermore, results suggested that individuals with differing mechanisms of anomia could derive benefits from participation in SFA-focused group treatment. Aims: The aim of the current study was to investigate further training of SFA in connected speech during group aphasia treatment. This study expanded and extended previous work (Antonucci, 2009), through the addition of participants with more varied aetiologies and severities of aphasia, and through the introduction of home practice. It was hypothesised that lexical retrieval during discourse would improve, as would overall communicative informativeness and/or efficiency. Methods & Procedures: Four individuals with aphasia participated in biweekly group treatment during which SFA was trained through connected speech tasks. Three participants presented with stroke aphasia, while one demonstrated aphasia consequent to traumatic brain injury. Discourse measures included those for overall communicative informativeness and efficiency (Nicholas & Brookshire, 1993) and for word-class-specific lexical retrieval (Mayer & Murray, 2003). Effect sizes were calculated for all discourse measures. Pre- and post-treatment performance on the spontaneous speech portion of the Western Aphasia Battery-Revised was also analysed relative to discourse measures, to corroborate findings from more frequently repeated probes. Outcomes & Results: All four participants demonstrated improvement to communicative informativeness and/or efficiency in connected speech tasks. Conclusions: Results provide additional support for the hypothesis that SFA administered during group aphasia treatment can be used successfully to facilitate improvement of communicative effectiveness. These results also support previous findings that individuals with differing aetiologies and natures of word retrieval impairment may benefit from participation in the same SFA-focused group aphasia treatment. Future work proceeding from this study may be directed towards differentiating which aspects of the treatment are most effective across participants with varied naming impairment, what is the optimal group composition and size, and towards discerning the most effective methods for facilitating and monitoring home practice.

Cortical and subcortical contributions to the attentive processing of speech

The neuroanatomical correlates of attentive listening were investigated with functional magnetic resonance imaging and an attention task in which listeners responded only to words that combined two specific attributes of voice and semantic content. This task was performed under two different attentive listening conditions: (i) diotically, with words presented sequentially, and (ii) dichotically, with male and female voices presented simultaneously but segregated to different ears. For both conditions, functional magnetic resonance imaging revealed bihemispheric but right-lateralized activity patterns in mid-prefrontal, anterior cingulate, and inferior parietal areas, as well as significant anterior insular and subcortical activation. Manipulating attentional demands under different listening conditions revealed an important role for right anterior insula, striatum, and thalamus in the regulation of attentive listening to spoken language.

A lifespan perspective on semantic processing of concrete concepts: does a sensory/motor model have the potential to bridge the gap?

Research regarding semantic knowledge of objects is often conducted independently in children and adults. Review of these bodies of evidence suggests that the two literatures are often complementary. It seems critical to determine what we can learn from a developmental perspective, toward the common goal of understanding semantic organization. Here we focus on the proposal that semantic knowledge about concrete concepts may be built on the foundation of sensory/motor processes. In particular, we focus on a moderate formulation of this viewpoint, the sensory/motor model of semantic representations of objects (e.g., Gainotti 2007; Martin 2007), which has been examined utilizing behavioral, neuroimaging, and neuropsychological evidence. Taken together, behavioral and neuroimaging studies with infants, older children, and adults have suggested that patterns laid down in early childhood remain salient throughout the lifespan and may also predict patterns of deficit that emerge following brain injury.

Semantic Memory and Language Processing: A Primer

Semantic memory refers to our long-term knowledge of word and object meaning. There is increasing evidence that rather than being a passive warehouse of knowledge, semantic memory is a dynamic system whose effectiveness relies on the coordination of multiple components distributed across a large network of cortical regions. Damage to one or more of these components produces distinct profiles of impairment in aphasia and dementia. Furthermore, such differences are associated with different responses to behavioral treatment. That is, effective treatment for semantically based language disorders in aphasia may have very limited success in dementia. We argue that treatment specificity demands a comprehensive understanding of the structure of semantic memory and the nature of its compromise. Here, we review several neuroanatomically informed theories of semantic organization with respect to the effects of semantic impairment on language processing in aphasia and neurodegenerative disease.

Anomia in patients with left inferior temporal lobe lesions

Background: Damage to left inferior temporal cortex has been associated with naming deficits resulting either from impaired access to phonological word forms (pure anomia) or from degraded semantic knowledge (semantic anomia). Neuropsychological evidence indicates that pure anomia may follow damage to posterior inferior temporal cortex (BA 37), whereas semantic anomia is associated with damage to more anterior temporal lobe regions (BA 20, 21, 38). By contrast, some investigators have suggested that it is the overall severity of anomia, rather than the nature of the underlying cognitive impairment, that is affected by the anterior extent of the lesion. Aims: To examine the naming performance of patients with left inferior temporal lobe damage and determine whether anterior extension of the lesion influences the nature and/or the severity of the naming impairment. Methods & Procedures: Eight participants with focal damage to left inferior temporal cortex completed a battery of language measures that included confrontation naming, semantic processing, and single‐word reading and spelling. Degree and type of anomia was examined relative to anterior lesion extension using both visual inspection and statistical analyses. Outcomes & Results: Naming performance ranged from unimpaired to severely defective, with only two participants demonstrating an additional mild impairment of semantic knowledge. The underlying mechanism of anomia seemed to be degraded access to phonological word forms in all participants, regardless of lesion configuration. The severity of the naming impairment was positively correlated with anterior extension of the lesion towards the temporal pole, although additional analyses suggested that these findings were significantly influenced by participant age. Naming was not correlated with performance on the nonverbal semantic task or any other demographic variable. Conclusions: The behavioural and neuroanatomical findings provide modest support for the hypothesis that a relationship exists between anterior lesion extension and the severity of concomitant anomia in patients with left inferior temporal lobe damage. The data suggest that such lesions may disconnect relatively preserved semantic knowledge from regions critical for access to phonological word forms. However, additional research is needed to discern to what extent age and individual variability temper these effects.

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.

Modulating the focus of attention for spoken words at encoding affects frontoparietal activation for incidental verbal memory

Attention is crucial for encoding information into memory, and current dual-process models seek to explain the roles of attention in both recollection memory and incidental-perceptual memory processes. The present study combined an incidental memory paradigm with event-related functional MRI to examine the effect of attention at encoding on the subsequent neural activation associated with unintended perceptual memory for spoken words. At encoding, we systematically varied attention levels as listeners heard a list of single English nouns. We then presented these words again in the context of a recognition task and assessed the effect of modulating attention at encoding on the BOLD responses to words that were either attended strongly, weakly, or not heard previously. MRI revealed activity in right-lateralized inferior parietal and prefrontal regions, and positive BOLD signals varied with the relative level of attention present at encoding. Temporal analysis of hemodynamic responses further showed that the time course of BOLD activity was modulated differentially by unintentionally encoded words compared to novel items. Our findings largely support current models of memory consolidation and retrieval, but they also provide fresh evidence for hemispheric differences and functional subdivisions in right frontoparietal attention networks that help shape auditory episodic recall.