Adelyn Brecher

Anterior temporal involvement in semantic word retrieval: voxel-based lesion-symptom mapping evidence from aphasia

Analysis of error types provides useful information about the stages and processes involved in normal and aphasic word production. In picture naming, semantic errors (horse for goat) generally result from something having gone awry in lexical access such that the right concept was mapped to the wrong word. This study used the new lesion analysis technique known as voxel-based lesion-symptom mapping to investigate the locus of lesions that give rise to semantic naming errors. Semantic errors were obtained from 64 individuals with post-stroke aphasia, who also underwent high-resolution structural brain scans. Whole brain voxel-based lesion-symptom mapping was carried out to determine where lesion status predicted semantic error rate. The strongest associations were found in the left anterior to mid middle temporal gyrus. This area also showed strong and significant effects in further analyses that statistically controlled for deficits in pre-lexical, conceptualization processes that might have contributed to semantic error production. This study is the first to demonstrate a specific and necessary role for the left anterior temporal lobe in mapping concepts to words in production. We hypothesize that this role consists in the conveyance of fine-grained semantic distinctions to the lexical system. Our results line up with evidence from semantic dementia, the convergence zone framework and meta-analyses of neuroimaging studies on word production. At the same time, they cast doubt on the classical linkage of semantic error production to lesions in and around Wernickes area.

Neuroanatomical dissociation for taxonomic and thematic knowledge in the human brain.

It is thought that semantic memory represents taxonomic information differently from thematic information. This study investigated the neural basis for the taxonomic-thematic distinction in a unique way. We gathered picture-naming errors from 86 individuals with poststroke language impairment (aphasia). Error rates were determined separately for taxonomic errors (“pear” in response to apple) and thematic errors (“worm” in response to apple), and their shared variance was regressed out of each measure. With the segmented lesions normalized to a common template, we carried out voxel-based lesion-symptom mapping on each error type separately. We found that taxonomic errors localized to the left anterior temporal lobe and thematic errors localized to the left temporoparietal junction. This is an indication that the contribution of these regions to semantic memory cleaves along taxonomic-thematic lines. Our findings show that a distinction long recognized in the psychological sciences is grounded in the structure and function of the human brain.

Computer-assisted treatment of word retrieval deficits in aphasia

Background : There are now numerous experimental studies demonstrating successful treatment of word retrieval deficits in aphasia. Technological advances allow us to implement many of these approaches on the computer and target the underlying impairment (e.g., in phonologically vs semantically based retrieval deficits). These computer-assisted treatments have the potential to facilitate the work of clinicians and, if geared towards independent or volunteer-assisted usage, extend the rehabilitation process beyond the period of formal therapy. Aims : Our aim is to review the benefits and limitations of computer-assisted treatment for word retrieval deficits, focusing on the lessons we have learned from a computerised therapy system, developed in our laboratory, which was designed to be used in the clinical setting, as well as by patients working independently. Contributions : We review relevant single and multiple case studies that use computer-assisted treatment programmes in various clinical and home settings. We then describe an outcome study that used the therapy system developed in our laboratory to deliver a hierarchical, multi-modality cueing protocol under clinician-guided and self-guided instruction. Through the use of mini case studies, we exemplify the systems application in the clinical setting and in home usage. Additionally we present use and satisfaction data which impact on clinical and home use. Conclusions : Theoretically motivated, computer-assisted treatments for naming impairments can be beneficial as an adjunct to one-on-one speech/language therapy, and are an effective way to intensify and continue the rehabilitation process. While many of our patients are capable of working independently or with minimal assistance to achieve their goals, computers still represent an unfamiliar and intimidating technology for the majority of our patients and families; and access in the home remains limited. One way to provide needed support is through a computer lab, staffed by trained volunteers working under the supervision of a speech-language pathologist. Additional research is needed to replicate these findings with a larger and more diverse group of individuals with aphasia and to evaluate the effectiveness of the Multi-modality Matching Module of MossTalk Words® software in the treatment of semantically based anomia. This could potentially provide pilot data for a large-scale clinical trial.

A Model-Driven Analysis of Severity, Response Characteristics, and Partial Recovery in Aphasics' Picture Naming☆

Dell, Schwartz, Martin, Saffran, and Gagnon (DSMSG; 1997) presented a computational analysis of aphasic naming that, among other things, purports to explain why some error types correlate with naming severity while others do not. It does so in terms of chance response opportunities, which differ among error types and which come into play particularly when activation levels are small. The present study looks at error frequencies in relation to severity at two points in time: at study entry and after a period of partial recovery. Results support the models distinction between severity-sensitive errors (nonwords. formal paraphasias, and unrelated errors) and those that are severity insensitive (semantic; mixed). Additionally, we show that the degree of target overlap in nonwords is sensitive to severity but various measures of monitoring and error correction are not. While these results generally support DSMSG, effects at the level of individual patients underscore the difficulties that their model encounters in explaining some pure error dissociations.

Errors of lexical selection during high and low semantic competition

In the ‘‘paced-cyclic’’ naming paradigm participants take longer to name a repeated series of pictures when the pictures are from the same semantic category vs. mixed categories, presumably due to semantically mediated competition for lexical selection (Damian, Vigliocco, & Levelt, 2001). Thompson-Schill’s selection hypothesis (ThompsonSchill et al., 1998) maintains that anterior brain damage compromises selection when semantic competition is high. In keeping with this, two anterior aphasics were shown to produce more errors in the homogeneous compared to mixed condition of paced-cyclic naming (McCarthy & Kartsounis, 2000; Wilshire & McCarthy, 2002). The present study replicated and extended this finding using a group study design. It also used error-type analysis to test the hypothesis that competition is the basis for higher error rates in the homogeneous contexts [see McCarthy and Kartsounis (2000) for alternative].