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1.  The Ins and Outs of Meaning: Behavioral and Neuroanatomical Dissociation of Semantically-Driven Word Retrieval and Multimodal Semantic Recognition in Aphasia 
Neuropsychologia  2015;76:208-219.
Theories about the architecture of language processing differ with regard to whether verbal and nonverbal comprehension share a functional and neural substrate and how meaning extraction in comprehension relates to the ability to use meaning to drive verbal production. We (re-)evaluate data from 17 cognitive-linguistic performance measures of 99 participants with chronic aphasia using factor analysis to establish functional components and support vector regression-based lesion-symptom mapping to determine the neural correlates of deficits on these functional components. The results are highly consistent with our previous findings: production of semantic errors is behaviorally and neuroanatomically distinct from verbal and nonverbal comprehension. Semantic errors were most strongly associated with left ATL damage whereas deficits on tests of verbal and non-verbal semantic recognition were most strongly associated with damage to deep white matter underlying the frontal lobe at the confluence of multiple tracts, including the inferior fronto-occipital fasciculus, the uncinate fasciculus, and the anterior thalamic radiations. These results suggest that traditional views based on grey matter hub(s) for semantic processing are incomplete and that the role of white matter in semantic cognition has been underappreciated.
doi:10.1016/j.neuropsychologia.2015.02.014
PMCID: PMC4534364  PMID: 25681739
semantic memory; comprehension; semantic errors; lesion-symptom mapping; aphasia; white matter
2.  The Marin Lab at the Dawn of Cognitive Neuropsychology 
This essay discusses the intellectual developments in psychology, linguistics, and behavioral neurology that shaped Oscar Marin’s approach to disorders of high cortical function. As Chief of Neurology at Baltimore City Hospitals in the 1970s, Dr Marin teamed with biopsychologist Eleanor Saffran and the author in seminal studies of acquired language disorders (aphasia) centering on core processes of syntax and semantics, and rejecting premature reductionism. The philosophical and methodological principles that motivated these studies are traced through the author’s personal recollections and the published writings of the Marin lab. These principles came to be associated with the cognitive neuropsychology school of research and have important linkages to contemporary work in the neuroscience of aphasia and related cognitive disorders.
doi:10.1097/WNN.0000000000000062
PMCID: PMC4588055  PMID: 26413736
Oscar Marin; aphasia; cognitive neuropsychology; single-case studies; levels of analysis
3.  Neural Organization of Spoken Language Revealed by Lesion-Symptom Mapping 
Nature communications  2015;6:6762.
Studies of patients with acquired cognitive deficits following brain damage and studies using contemporary neuroimaging techniques form two distinct streams of research on the neural basis of cognition. In this study, we combine high-quality structural neuroimaging analysis techniques and extensive behavioral assessment of patients with persistent acquired language deficits to study the neural basis of language. Our results reveal two major divisions within the language system – meaning vs. form and recognition vs. production – and their instantiation in the brain. Phonological form deficits are associated with lesions in peri-Sylvian regions, whereas semantic production and recognition deficits are associated with damage to the left anterior temporal lobe and white matter connectivity with frontal cortex, respectively. These findings provide a novel synthesis of traditional and contemporary views of the cognitive and neural architecture of language processing, emphasizing dual-routes for speech processing and convergence of white matter tracts for semantic control and/or integration.
doi:10.1038/ncomms7762
PMCID: PMC4400840  PMID: 25879574
4.  The dorsal stream contribution to phonological retrieval in object naming 
Brain  2012;135(12):3799-3814.
Meaningful speech, as exemplified in object naming, calls on knowledge of the mappings between word meanings and phonological forms. Phonological errors in naming (e.g. GHOST named as ‘goath’) are commonly seen in persisting post-stroke aphasia and are thought to signal impairment in retrieval of phonological form information. We performed a voxel-based lesion-symptom mapping analysis of 1718 phonological naming errors collected from 106 individuals with diverse profiles of aphasia. Voxels in which lesion status correlated with phonological error rates localized to dorsal stream areas, in keeping with classical and contemporary brain-language models. Within the dorsal stream, the critical voxels were concentrated in premotor cortex, pre- and postcentral gyri and supramarginal gyrus with minimal extension into auditory-related posterior temporal and temporo-parietal cortices. This challenges the popular notion that error-free phonological retrieval requires guidance from sensory traces stored in posterior auditory regions and points instead to sensory-motor processes located further anterior in the dorsal stream. In a separate analysis, we compared the lesion maps for phonological and semantic errors and determined that there was no spatial overlap, demonstrating that the brain segregates phonological and semantic retrieval operations in word production.
doi:10.1093/brain/aws300
PMCID: PMC3525060  PMID: 23171662
aphasia; dual-stream; voxel-based lesion-symptom mapping; naming; phonological errors; semantic errors
5.  Short form Philadelphia Naming Test: Rationale and Empirical Evaluation 
Purpose
To create two matched short forms of the Philadelphia Naming Test (PNT) that yield similar results to the PNT for measuring anomia.
Methods
Study 1: We first used archived naming data from 94 aphasic individuals to identify which PNT items should be included in the short forms, and the two constructed sets of 30 items, PNT30-A and PNT30-B, were validated using archived data from a separate group of 56 aphasic individuals. Study 2: We then evaluated the reliability of the PNT, PNT30-A, and PNT30-B across independent test administrations with a new group of 25 aphasic individuals selected to represent the full range of naming impairment.
Results
Study 1: PNT30-A and PNT30-B were found to be internally consistent; and accuracy scores on these subsets of items were highly correlated with the full PNT. Study 2: PNT accuracy was extremely reliable over the span of one week; and independent administrations of PNT30-A and PNT30-B produced similar results to the PNT and to each other.
Conclusions
The short forms can be used to reliably estimate PNT performance, and the results can be compared to the provided norms. The two matched tests allow for measurement of change in naming ability.
doi:10.1044/1058-0360(2012/11-0089)
PMCID: PMC3397242  PMID: 22294412
Aphasia; Assessment; Speech production; Stroke
6.  A large, searchable, web-based database of aphasic performance on picture naming and other tests of cognitive function 
Cognitive neuropsychology  2011;27(6):495-504.
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/.
doi:10.1080/02643294.2011.574112
PMCID: PMC3162111  PMID: 21714742
aphasia; database; picture naming; language
7.  Case Series Investigations in Cognitive Neuropsychology 
Cognitive neuropsychology  2011;27(6):477-494.
Case series methodology involves the systematic assessment of a sample of related patients, with the goal of understanding how and why they differ from one another. This method has become increasingly important in cognitive neuropsychology, which has long been identified with single-subject research. We review case series studies dealing with impaired semantic memory, reading, and language production, and draw attention to the affinity of this methodology for testing theories that are expressed as computational models and for addressing questions about neuroanatomy. It is concluded that case series methods usefully complement single-subject techniques.
doi:10.1080/02643294.2011.574111
PMCID: PMC3162112  PMID: 21714756
case series; single-subject; cognitive neuropsychology; computational models; lexical access; semantic dementia; aphasia; semantic memory
8.  Anterior temporal involvement in semantic word retrieval: voxel-based lesion-symptom mapping evidence from aphasia 
Brain  2009;132(12):3411-3427.
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.
doi:10.1093/brain/awp284
PMCID: PMC2792374  PMID: 19942676
aphasia; voxel-based lesion-symptom mapping; naming; semantic; errors
9.  A Case-Series Test of the Interactive Two-step Model of Lexical Access: Predicting Word Repetition from Picture Naming 
Journal of memory and language  2007;56(4):490-520.
Lexical access in language production, and particularly pathologies of lexical access, are often investigated by examining errors in picture naming and word repetition. In this article, we test a computational approach to lexical access, the two-step interactive model, by examining whether the model can quantitatively predict the repetition-error patterns of 65 aphasic subjects from their naming errors. The model’s characterizations of the subjects’ naming errors were taken from the companion paper to this one (Schwartz, Dell, N. Martin, Gahl & Sobel, 2006), and their repetition was predicted from the model on the assumption that naming involves two error prone steps, word and phonological retrieval, whereas repetition only creates errors in the second of these steps. A version of the model in which lexical-semantic and lexical-phonological connections could be independently lesioned was generally successful in predicting repetition for the aphasics. An analysis of the few cases in which model predictions were inaccurate revealed the role of input phonology in the repetition task.
doi:10.1016/j.jml.2006.05.007
PMCID: PMC2981040  PMID: 21085621
10.  Test-Enhanced Learning Versus Errorless Learning in Aphasia Rehabilitation: Testing Competing Psychological Principles 
Because individuals with acquired language disorders are frequently unable to reliably access the names of common everyday objects (i.e., naming impairment), rehabilitation efforts often focus on improving naming. The present study compared two rehabilitation strategies for naming impairment, reflecting contradictory prescriptions derived from different theoretical principles. The prescription derived from psychological research on test-enhanced learning advocates providing patients opportunities to retrieve target names from long-term memory (i.e., retrieval practice) in the course of treatment. In contrast, the errorless learning approach derived from cognitive rehabilitation research eschews retrieval practice in favor of methods that minimize naming errors, and thus the potential for error learning, in the course of treatment. The present study directly compared these approaches and showed that, despite superior (and errorless) performance during errorless treatment, treatment that prioritized retrieval practice produced greater retention 1-day and 1-week following treatment. These findings have implications for clinical practice, as well as theoretical accounts of lexical access and test-enhanced learning.
doi:10.1037/xlm0000091
PMCID: PMC4476962  PMID: 25528093
naming; aphasia; test-enhanced learning; errorless learning; lexical access
11.  Temporal Characteristics of Semantic Perseverations Induced by Blocked-Cyclic Picture Naming 
Brain and language  2009;108(3):133-144.
When unimpaired participants name pictures quickly, they produce many perseverations that bear a semantic relation to the target, especially when the pictures are blocked by semantic category. These “semantic perseverations” have not shown the steep decay over lags (distance from prior occurrence) that typify the perseverations produced by people with aphasia on standard naming tasks (Cohen & Dehaene, 1998). To reconcile the discrepant findings, we studied semantic perseverations generated by participants with aphasia on a naming task that featured semantic blocking [Schnur, T. T., Schwartz, M. F., Brecher, A., & Hodgson, C. (2006). Semantic interference during blocked-cyclic naming: Evidence from aphasia. Journal of Memory and Language, 54, 199–227]. The temporal properties of these perseverations were investigated by analyzing their lag function and the influence of time (response-stimulus interval) on this function. To separate out the influence of chance on the observed lag distributions, chance data sets were created for individual participants by reshuffling whole trials (i.e., stimulus-response pairs) in a manner that preserved unique features of the blocking design. Analyses of chance-corrected lag functions revealed the expected recency bias, i.e., higher perseveration frequencies at short lags. Importantly, there was no difference between the lag functions for perseverations generated with a 5 s, compared to 1 s, response-stimulus interval. This combination of recency and insensitivity to elapsed time indicates that the perseveratory impetus in a named response does not passively decay with time but rather is diminished by interference from related trials. We offer an incremental learning account of these findings.
doi:10.1016/j.bandl.2008.11.003
PMCID: PMC2642906  PMID: 19138794
Perseveration; semantic blocking; aphasia; naming; priming; incremental learning
12.  Theoretical analysis of word production deficits in adult aphasia 
The cognitive analysis of adult language disorders continues to draw heavily on linguistic theory, but increasingly it reflects the influence of connectionist, spreading activation models of cognition. In the area of spoken word production, ‘localist’ connectionist models represent a natural evolution from the psycholingistic theories of earlier decades. By contrast, the parallel distributed processing framework forces more radical rethinking of aphasic impairments. This paper exemplifies these multiple influences in contemporary cognitive aphasiology. Topics include (i) what aphasia reveals about semantic-phonological interaction in lexical access; (ii) controversies surrounding the interpretation of semantic errors and (iii) a computational account of the relationship between naming and word repetition in aphasia. Several of these topics have been addressed using case series methods, including computational simulation of the individual, quantitative error patterns of diverse groups of patients and analysis of brain lesions that correlate with error rates and patterns. Efforts to map the lesion correlates of nonword errors in naming and repetition highlight the involvement of sensorimotor areas in the brain and suggest the need to better integrate models of word production with models of speech and action.
doi:10.1098/rstb.2012.0390
PMCID: PMC3866420  PMID: 24324234
aphasia; naming; repetition; errors; semantic; phonological
13.  Multivariate Lesion-Symptom Mapping Using Support Vector Regression 
Human brain mapping  2014;35(12):5861-5876.
Lesion analysis is a classic approach to study brain functions. Because brain function is a result of coherent activations of a collection of functionally related voxels, lesion-symptom relations are generally contributed by multiple voxels simultaneously. Although voxel-based lesion symptom mapping (VLSM) has made substantial contributions to the understanding of brain-behavior relationships, a better understanding of the brain-behavior relationship contributed by multiple brain regions needs a multivariate lesion symptom mapping (MLSM). The purpose of this paper was to develop an MLSM using a machine learning-based multivariate regression algorithm: support vector regression (SVR). In the proposed SVR-LSM, the symptom relation to the entire lesion map as opposed to each isolated voxel is modeled using a non-linear function, so the inter-voxel correlations are intrinsically considered, resulting in a potentially more sensitive way to examine lesion-symptom relationships. To explore the relative merits of VLSM and SVR-LSM we used both approaches in the analysis of a synthetic dataset. SVR-LSM showed much higher sensitivity and specificity for detecting the synthetic lesion-behavior relations than VLSM. When applied to lesion data and language measures from patients with brain damages, SVR-LSM reproduced the essential pattern of previous findings identified by VLSM and showed higher sensitivity than VLSM for identifying the lesion-behavior relations. Our data also showed the possibility of using lesion data to predict continuous behavior scores.
doi:10.1002/hbm.22590
PMCID: PMC4213345  PMID: 25044213
Lesion-symptom mapping; support vector regression; aphasia; total lesion volume control
14.  Voxel-based lesion-parameter mapping: Identifying the neural correlates of a computational model of word production 
Cognition  2013;128(3):380-396.
The dual-route interactive two-step model explains the variation in the error patterns of aphasic speakers in picture naming, and word and nonword repetition tasks. The model has three parameters that can vary across individuals: the efficiency of the connections between semantic and lexical representations (s-weight), between lexical and phonological representations (p-weight), and between representations of auditory input and phonological representations (nl-weight). We determined these parameter values in 103 participants with chronic aphasia from left hemisphere stroke whose lesion locations had been determined. Then, using voxel-based lesion-parameter mapping, we mapped the parameters onto the brain, thus determining the neural correlates of the model’s mechanisms. The maps and the behavioral findings supported the model’s central claim that word repetition is affected by both the p and nl parameters. We propose that these two parameters constitute the model’s analogue of the “dorsal stream” component of neurocognitive models of language processing.
doi:10.1016/j.cognition.2013.05.007
PMCID: PMC3709005  PMID: 23765000
Aphasia; Language production; Computational models; Voxel-based Lesion Parameter Mapping
15.  Learning to Fail in Aphasia: An Investigation of Error Learning in Naming 
Purpose
To determine if the naming impairment in aphasia is influenced by error learning and if error learning is related to type of retrieval strategy.
Method
Nine participants with aphasia and ten neurologically-intact controls named familiar proper noun concepts. When experiencing tip-of-the-tongue naming failure (TOT) in an initial TOT-elicitation phase, participants were instructed to adopt phonological or semantic self-cued retrieval strategies. In the error learning manipulation, items evoking TOT states during TOT-elicitation were randomly assigned to a short or long time condition where participants were encouraged to continue to try to retrieve the name for either 20 seconds (short interval) or 60 seconds (long). The incidence of TOT on the same items was measured on a post test after 48-hours. Error learning was defined as a higher rate of recurrent TOTs (TOT at both TOT-elicitation and post test) for items assigned to the long (versus short) time condition.
Results
In the phonological condition, participants with aphasia showed error learning whereas controls showed a pattern opposite to error learning. There was no evidence for error learning in the semantic condition for either group.
Conclusion
Error learning is operative in aphasia, but dependent on the type of strategy employed during naming failure.
doi:10.1044/1092-4388(2012/12-0220)
PMCID: PMC3781174  PMID: 23816662
aphasia; naming; error learning; errorless; cueing; semantic; phonological; tip-of-the-tongue
16.  Subdivision of frontal cortex mechanisms for language production in aphasia 
Neuropsychologia  2012;50(14):3284-3294.
Ventrolateral prefrontal cortex (VLPFC) has long been linked to language production, but the precise mechanisms are still being elucidated. Using neuropsychological case studies, we explored possible sub-specialization within this region for different linguistic and executive functions. Frontal patients with different lesion profiles completed two sequencing tasks, which were hypothesized to engage partially overlapping components. The multi-word priming task tested the sequencing of co-activated representations and the overriding of primed word orders. The sequence reproduction task tested the sequencing of co-activated representations, but did not employ a priming manipulation. We compared patients’ performance on the two tasks to that of healthy, age-matched controls. Results are partially consistent with an anterior-posterior gradient of cognitive control within lateral prefrontal cortex (Koechlin & Summerfield, 2007). However, we also found a stimulus-specific pattern, which suggests that sub-specialization might be contingent on type of representation as well as type of control signal. Isolating such components functionally and anatomically might lead to a better understanding of language production deficits in aphasia.
doi:10.1016/j.neuropsychologia.2012.09.021
PMCID: PMC3518563  PMID: 23022077
language production; sequencing; cognitive control; prefrontal cortex; aphasia
17.  Errorless Learning in Cognitive Rehabilitation: A Critical Review 
Neuropsychological Rehabilitation  2012;22(2):138-168.
Cognitive rehabilitation research is increasingly exploring errorless learning interventions, which prioritize the avoidance of errors during treatment. The errorless learning approach was originally developed for patients with severe anterograde amnesia, who were deemed to be at particular risk for error learning. Errorless learning has since been investigated in other memory-impaired populations (e.g., Alzheimer's disease) and acquired aphasia. In typical errorless training, target information is presented to the participant for study or immediate reproduction, a method that prevents participants from attempting to retrieve target information from long-term memory (i.e., retrieval practice). However, assuring error elimination by preventing difficult (and error-permitting) retrieval practice is a potential major drawback of the errorless approach. This review begins with discussion of research in the psychology of learning and memory that demonstrates the importance of difficult (and potentially errorful) retrieval practice for robust learning and prolonged performance gains. We then review treatment research comparing errorless and errorful methods in amnesia and aphasia, where only the latter provides (difficult) retrieval practice opportunities. In each clinical domain we find the advantage of the errorless approach is limited and may be offset by the therapeutic potential of retrieval practice. Gaps in current knowledge are identified that preclude strong conclusions regarding a preference for errorless treatments over methods that prioritize difficult retrieval practice. We offer recommendations for future research aimed at a strong test of errorless learning treatments, which involves direct comparison with methods where retrieval practice effects are maximized for long-term gains.
doi:10.1080/09602011.2011.639619
PMCID: PMC3381647  PMID: 22247957
errorless; errorful; retrieval practice; testing; spacing; aphasia; amnesia
19.  Is comprehension necessary for error detection? A conflict-based account of monitoring in speech production 
Cognitive psychology  2011;63(1):1-33.
Despite the existence of speech errors, verbal communication is successful because speakers can detect (and correct) their errors. The standard theory of speech-error detection, the perceptual-loop account, posits that the comprehension system monitors production output for errors. Such a comprehension-based monitor, however, cannot explain the double dissociation between comprehension and error-detection ability observed in the aphasic patients. We propose a new theory of speech-error detection which is instead based on the production process itself. The theory borrows from studies of forced-choice-response tasks the notion that error detection is accomplished by monitoring response conflict via a frontal brain structure, such as the anterior cingulate cortex. We adapt this idea to the two-step model of word production, and test the model-derived predictions on a sample of aphasic patients. Our results show a strong correlation between patients’ error-detection ability and the model’s characterization of their production skills, and no significant correlation between error detection and comprehension measures, thus supporting a production-based monitor, generally, and the implemented conflict-based monitor in particular. The successful application of the conflict-based theory to error-detection in linguistic, as well as non-linguistic domains points to a domain-general monitoring system.
doi:10.1016/j.cogpsych.2011.05.001
PMCID: PMC3135428  PMID: 21652015
Speech monitoring; Speech errors; Error detection; Aphasia; Computational models
20.  The neural basis of reversible sentence comprehension: Evidence from voxel-based lesion-symptom mapping in aphasia 
Journal of Cognitive Neuroscience  2011;24(1):212-222.
We explored the neural basis of reversible sentence comprehension in a large group of aphasic patients (N=79). Voxel-based lesion-symptom mapping revealed a significant association between damage in temporoparietal cortex and impaired sentence comprehension. This association remained after we controlled for phonological working memory. We hypothesize that this region plays an important role in the thematic or what-where processing of sentences. In contrast, we detected weak or no association between reversible sentence comprehension and the ventrolateral prefrontal cortex, which includes Broca’s area, even for syntactically complex sentences. This casts doubt on theories that presuppose a critical role for this region in syntactic computations.
doi:10.1162/jocn_a_00118
PMCID: PMC3389786  PMID: 21861679
Broca’s area; Prefrontal; Temporoparietal; Thematic Roles; Syntax
21.  Support for Anterior Temporal Involvement in Semantic Error Production in Aphasia: New Evidence from VLSM 
Brain and language  2010;117(3):110-122.
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.
doi:10.1016/j.bandl.2010.09.008
PMCID: PMC3037437  PMID: 20961612
aphasia; voxel-based lesion-symptom mapping; naming; semantic; errors
22.  Naming and repetition in aphasia: Steps, routes, and frequency effects 
Journal of memory and language  2010;63(4):541-559.
This paper investigates the cognitive processes underlying picture naming and auditory word repetition. In the 2-step model of lexical access, both the semantic and phonological steps are involved in naming, but the former has no role in repetition. Assuming recognition of the to-be-repeated word, repetition could consist of retrieving the word’s output phonemes from the lexicon (the lexical-route model), retrieving the output phonology directly from input phonology (the nonlexical-route model) or employing both routes together (the summation dual-route model). We tested these accounts by comparing the size of the word frequency effect (an index of lexical retrieval) in naming and repetition data from 59 aphasic patients with simulations of naming and repetition models. The magnitude of the frequency effect (and the influence of other lexical variables) was found to be comparable in naming and repetition, and equally large for both the lexical and summation dual-route models. However, only the dual-route model was fully consistent with data from patients, suggesting that nonlexical input is added on top of a fully-utilized lexical route.
doi:10.1016/j.jml.2010.08.001
PMCID: PMC2976549  PMID: 21076661
Lexical access; Aphasia; Repetition; Picture naming; Computational models; Case-series; Word frequency
23.  Density Pervades: An Analysis of Phonological Neighborhood Density Effects in Aphasic Speakers with Different Types of Naming Impairment 
Cognitive neuropsychology  2010;27(5):401-427.
We investigated the influence of phonological neighborhood density (PND) on the performance of aphasic speakers whose naming impairments differentially implicate phonological or semantic stages of lexical access. A word comes from a dense phonological neighborhood if many words sound like it. Limited evidence suggests that higher density facilitates naming in aphasic speakers, as it does in healthy speakers. Using well controlled stimuli, Experiment 1 confirmed the influence of PND on accuracy and phonological error rates in two aphasic speakers with phonological processing deficits. In Experiments 2 and 3, we extended the investigation to an aphasic speaker who is prone to semantic errors, indicating a semantic deficit and/or a deficit in the mapping from semantics to words. This individual had higher accuracy, and fewer semantic errors, in naming targets from high versus low density neighborhoods. It is argued that the results provide strong support for interactive approaches to lexical access, where reverberatory feedback between word- and phoneme-level lexical representations not only facilitates phonological level processes but also privileges the selection of a target word over its semantic competitors.
doi:10.1080/02643294.2011.570325
PMCID: PMC3132149  PMID: 21718214
phonology; neighborhood density; aphasia; interactivity; lexical access
24.  Selection for position: The role of left ventrolateral prefrontal cortex in sequencing language 
Brain and language  2010;113(1):28-38.
Patients with damage involving left ventrolateral prefrontal cortex (left VLPFC) often show syntactic deficits. They also show exaggerated interference effects during a variety of non-syntactic tasks, including picture naming and working memory. Conceivably, both deficits could arise from inadequate biasing of competitive interactions during language production. To test this hypothesis, we manipulated “positional” interference during multiword naming by priming one of the nouns in the same or different position. Experimental case studies of four left VLPFC patients revealed that two of the patients showed exaggerated positional interference, greater number of errors, including omissions during multiword production, increased production difficulty when the order of nouns did not match the predominant English pattern as well as impaired comprehension of non-canonical reversible sentences. These results suggest that these two patients had an impairment in “selection for position”. Different from the other two, their lesions included a subregion of frontal cortex (BA 44/6) that has been shown in neuroimaging studies to pay a role in sequencing.
doi:10.1016/j.bandl.2010.01.002
PMCID: PMC2849107  PMID: 20149424
aphasia; language; production; syntax; sequencing; interference; prefrontal
25.  Reduced Short-Term Memory Span in Aphasia and Susceptibility to Interference: Contribution of Material-Specific Maintenance Deficits 
Neuropsychologia  2009;48(4):909-920.
Semantic short-term memory (STM) deficits have been traditionally defined as an inability to maintain semantic representations over a delay (R. Martin, Shelton & Yaffee, 1994). Yet some patients with semantic STM deficits make numerous intrusions of items from previously presented lists, thus presenting an interesting paradox: Why should an inability to maintain semantic representations produce an increase in intrusions from earlier lists? In this study, we investigated the relationship between maintenance deficits and susceptibility to interference in a group of 20 aphasic patients characterized with weak semantic or weak phonological STM. Patients and matched control participants performed a modified item-recognition task designed to elicit semantic or phonological interference from list items located one, two, or three trials back (Hamilton & R. Martin, 2007). Controls demonstrated significant effects of interference in both versions of the task. Interference in patients was predicted by the type and severity of their STM deficit; that is, shorter semantic spans were associated with greater semantic interference and shorter phonological spans were associated with greater phonological interference. We interpret these results through a new perspective, the reactivation hypothesis, and we discuss their importance for accounts emphasizing the contribution of maintenance mechanisms for STM impairments in aphasia as well as susceptibility to interference.
doi:10.1016/j.neuropsychologia.2009.11.010
PMCID: PMC2828523  PMID: 19925813
WORKING-MEMORY; RECENT-NEGATIVES; INHIBITION; SEMANTIC; PHONOLOGICAL

Results 1-25 (29)