Mapping articulatory and grammatical subcomponents of fluency deficits in post-stroke aphasia.

Fluent speech production is a critical aspect of language processing and is central to aphasia diagnosis and treatment. Multiple cognitive processes and neural subsystems must be coordinated to produce fluent narrative speech. To refine the understanding of these systems, measures that minimize the influence of other cognitive processes were defined for articulatory deficits and grammatical deficits. Articulatory deficits were measured by the proportion of phonetic errors (articulatory and prosodic) in a word repetition task in 115 participants with aphasia following left hemisphere stroke. Grammatical deficits were assessed in 46 participants based on two measures-proportion of closed class words and proportion of words in sentences-generated during semistructured narrative speech production (telling the Cinderella story). These measures were used to identify brain regions critical for articulatory and grammatical aspects of speech production using a multivariate lesion-symptom mapping approach based on support vector regression. Phonetic error proportion was associated with damage to the postcentral gyrus and the inferior parietal lobule (particularly the supramarginal gyrus). Proportion of closed class words in narrative speech did not have consistent lesion correlates. Proportion of words in sentences was strongly associated with frontal lobe damage, particularly the inferior and middle frontal gyri. Grammatical sentence structuring relies on frontal regions, particularly the inferior and middle frontal gyri, whereas phonetic-articulatory planning and execution relies on parietal regions, particularly the postcentral and supramarginal gyri. These results clarify and extend current understanding of the functional components of the frontoparietal speech production system.

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.

Learning from errors: Exploration of the monitoring learning effect.

The present study examined spontaneous detection and repair of naming errors in people with aphasia to advance a theoretical understanding of how monitoring impacts learning in lexical access. Prior work in aphasia has found that spontaneous repair, but not mere detection without repair, of semantic naming errors leads to improved naming on those same items in the future when other factors are accounted for. The present study sought to replicate this finding in a new, larger sample of participants and to examine the critical role of self-generated repair in this monitoring learning effect. Twenty-four participants with chronic aphasia with naming impairment provided naming responses to a 660-item corpus of common, everyday objects at two timepoints. At the first timepoint, a randomly selected subset of trials ended in experimenter-provided corrective feedback. Each naming trial was coded for accuracy, error type, and for any monitoring behavior that occurred, specifically detection with repair (i.e., correction), detection without repair, and no detection. Focusing on semantic errors, the original monitoring learning effect was replicated, with enhanced accuracy at a future timepoint when the first trial with that item involved detection with repair, compared to error trials that were not detected. This enhanced accuracy resulted from learning that arose from the first trial rather than the presence of repair simply signifying easier items. A second analysis compared learning from trials of self-corrected errors to that of trials ending in feedback that were detected but not self-corrected and found enhanced learning after self-generated repair. Implications for theories of lexical access and monitoring are discussed.

A large, searchable, web-based database of aphasic performance on picture naming and other tests of cognitive function.

Many research questions in aphasia can only be answered through access to substantial numbers of patients and to their responses on individual test items. Since such data are often unavailable to individual researchers and institutions, we have developed and made available the Moss Aphasia Psycholinguistics Project Database: a large, searchable, web-based database of patient performance on psycholinguistic and neuropsychological tests. The database contains data from over 240 patients covering a wide range of aphasia subtypes and severity, some of whom were tested multiple times. The core of the archive consists of a detailed record of individual-trial performance on the Philadelphia (picture) Naming Test. The database also contains basic demographic information about the patients and patients' overall performance on neuropsychological assessments as well as tests of speech perception, semantics, short-term memory, and sentence comprehension. The database is available at http://www.mappd.org/ .

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 Wernicke's area.

Does naming accuracy improve through self-monitoring of errors?

This study examined spontaneous self-monitoring of picture naming in people with aphasia. Of primary interest was whether spontaneous detection or repair of an error constitutes an error signal or other feedback that tunes the production system to the desired outcome. In other words, do acts of monitoring cause adaptive change in the language system? A second possibility, not incompatible with the first, is that monitoring is indicative of an item's representational strength, and strength is a causal factor in language change. Twelve PWA performed a 615-item naming test twice, in separate sessions, without extrinsic feedback. At each timepoint, we scored the first complete response for accuracy and error type and the remainder of the trial for verbalizations consistent with detection (e.g., "no, not that") and successful repair (i.e., correction). Data analysis centered on: (a) how often an item that was misnamed at one timepoint changed to correct at the other timepoint, as a function of monitoring; and (b) how monitoring impacted change scores in the Forward (Time 1 to Time 2) compared to Backward (Time 2 to Time 1) direction. The Strength hypothesis predicts significant effects of monitoring in both directions. The Learning hypothesis predicts greater effects in the Forward direction. These predictions were evaluated for three types of errors--Semantic errors, Phonological errors, and Fragments--using mixed-effects regression modeling with crossed random effects. Support for the Strength hypothesis was found for all three error types. Support for the Learning hypothesis was found for Semantic errors. All effects were due to error repair, not error detection. We discuss the theoretical and clinical implications of these novel findings.

Support for anterior temporal involvement in semantic error production in aphasia: new evidence from VLSM.

Semantic errors in aphasia (e.g., naming a horse as "dog") frequently arise from faulty mapping of concepts onto lexical items. A recent study by our group used voxel-based lesion-symptom mapping (VLSM) methods with 64 patients with chronic aphasia to identify voxels that carry an association with semantic errors. The strongest associations were found in the left anterior temporal lobe (L-ATL), in the mid- to anterior MTG region. The absence of findings in Wernicke's area was surprising, as were indications that ATL voxels made an essential contribution to the post-semantic stage of lexical access. In this follow-up study, we sought to validate these results by re-defining semantic errors in a manner that was less theory dependent and more consistent with prior lesion studies. As this change also increased the robustness of the dependent variable, it made it possible to perform additional statistical analyses that further refined the interpretation. The results strengthen the evidence for a causal relationship between ATL damage and lexically-based semantic errors in naming and lend confidence to the conclusion that chronic lesions in Wernicke's area are not causally implicated in semantic error production.

A patient registry for cognitive rehabilitation research: a strategy for balancing patients' privacy rights with researchers' need for access.

OBJECTIVE: To describe a consent-based Patient Research Registry designed to improve the quality and efficiency of cognitive rehabilitation research by balancing patients' privacy rights with researchers' need for access to research participants. DESIGN: Description of a protocol for a Patient Research Registry. SETTING: Three rehabilitation hospitals. PARTICIPANTS: Inpatients with stroke or traumatic brain injury (TBI) at the 3 participating hospitals. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Percentages of eligible patients with stroke or TBI who consented to be enrolled in the Registry, were subsequently contacted about a study, and ultimately participated in a study. A survey examined satisfaction with the Registry among researchers who used it for recruitment. RESULTS: After 36 months of operation, 58% of patients approached have consented to be in the Registry (N=1256). Eighty-seven percent of those later identified as potential subjects for research studies expressed interest, and 63% eventually participated. Researchers reported satisfaction with the recruitment opportunities afforded by the Registry. CONCLUSIONS: The Registry succeeded in identifying eligible patients interested in participating in research studies, while safeguarding their privacy rights. We identify its strengths and limitations and characterize the type of facility that would most profit from adopting this recruitment model.

Investigation of ethnic differences in willingness to enroll in a rehabilitation research registry: a study of the Northeast Cognitive Rehabilitation Research Network.

OBJECTIVE: To investigate differences between African American and white respondents in willingness to enroll in a rehabilitation research registry for future research and to determine if reasons for consenting and refusing to enroll differ by ethnicity. DESIGN: Inpatient recruitment results from 739 African American and white respondents in which patients were admitted to a rehabilitation hospital with a diagnosis of stroke or traumatic brain injury. RESULTS: A similar proportion of African American and white respondents (both patients and surrogates) consented to enroll in the registry (72% of all African American respondents vs. 68% of all white respondents). African Americans and whites provided similar reasons for consenting and refusing to enroll. Demographic variables associated with consent were: higher education, younger age, and facility. The odds of consenting to enroll in the registry were 5 times as high for those who thought they had a great deal to gain from enrollment compared with those who thought they had less to gain and were nearly 2 times as high for those who reported little concern about privacy compared with those who were more concerned about privacy. CONCLUSIONS: Ethnicity was not found to be a predictor of willingness to enroll in a study registry. A greater belief of gain and less concern over privacy were associated with willingness to enroll, even after controlling for age, education, facility, and ethnic group.