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.

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 taxonomicthematic lines. Our findings show that a distinction long recognized in the psychological sciences is grounded in the structure and function of the human brain.A fundamental question in cognitive neuroscience is how semantic knowledge is represented in the brain. We pursued this question by analyzing picture-naming errors generated by individuals with acquired language impairment (aphasia), focusing on errors that reflect the structure of semantic memory. When one views object A with the intention to name it, semantically related concepts B, C, and D come to mind along with A. These related concepts compete for access to the mental lexicon and occasionally stimulate the production of an error. Insight into the organization of semantic memory comes from analyzing the relations that link the target-error pairs.All types of speakers produce semantic errors when tasked with naming objects from pictures. In neurologically intact speakers, error rates are quite low unless special techniques are used to exaggerate the retrieval competition or force a speeded response (e.g., refs. 1 and 2). Across all types of speakers and all manner of testing, semantic naming errors overwhelmingly reflect taxonomic relations; that is, the predominant error is a category coordinate (apple named as "pear" or "grape"), superordinate (apple → "fruit"), or subordinate (apple → "Granny Smith"). A small subset are thematic errors, such as apple → "worm" or bone → "dog," in which the target and error are from different taxonomic categories but frequently play complementary roles in the same actions or events (1, 3).The distinction between taxonomic and thematic relations has been extensively researched in the psychology of concepts and conceptual relations (4, 5). Moreover, the distinction echoes the long-standing interest among philosophers in how similarity and contiguity organize the associative structure of the mind (e.g., ref. 6). Evidence from naming errors affords a rare opportunity to study how the taxonomic-thematic distinction manifests in language production. Most empirical research on this topic uses matching and sorting tasks that invoke explicit strat...

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.

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 170 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/.