Lexical access in aphasic and nonaphasic speakers

Do perceived context pictures automatically activate their phonological code?

Morsella and Miozzo (Morsella, E., & Miozzo, M. (2002). Evidence for a cascade model of lexical access in speech production. Journal of Experimental Psychology: Learning, Memory, and Cognition, 28, 555-563) have reported that the to-be-ignored context pictures become phonologically activated when participants name a target picture, and took this finding as support for cascaded models of lexical retrieval in speech production. In a replication and extension of their experiment in German, we failed to obtain priming effects from context pictures phonologically related to a to-be-named target picture. By contrast, corresponding context words (i.e., the names of the respective pictures) and the same context pictures, when used in an identity condition, did reliably facilitate the naming process. This pattern calls into question the generality of the claim advanced by Morsella and Miozzo that perceptual processing of pictures in the context of a naming task automatically leads to the activation of corresponding lexical-phonological codes.

Twisting tongues and memories: Explorations of the relationship between language production and verbal working memory

Many accounts of working memory posit specialized storage mechanisms for the maintenance of serial order. We explore an alternative, that maintenance is achieved through temporary activation in the language production architecture. Four experiments examined the extent to which the phonological similarity effect can be explained as a sublexical speech error. Phonologically similar nonword stimuli were ordered to create tongue twister or control materials used in four tasks: reading aloud, immediate spoken recall, immediate typed recall, and serial recognition. Dependent measures from working memory (recall accuracy) and language production (speech errors) fields were used. Even though lists were identical except for item order, robust effects of tongue twisters were observed. Speech error analyses showed that errors were better described as phoneme rather than item ordering errors. The distribution of speech errors was comparable across all experiments and exhibited syllable-position effects, suggesting an important role for production processes. Implications for working memory and language production are discussed.

Selective deficit of second language: a case study of a brain-damaged Arabic-Hebrew bilingual patient

BACKGROUND

An understanding of how two languages are represented in the human brain is best obtained from studies of bilingual patients who have sustained brain damage. The primary goal of the present study was to determine whether one or both languages of an Arabic-Hebrew bilingual individual are disrupted following brain damage. I present a case study of a bilingual patient, proficient in Arabic and Hebrew, who had sustained brain damage as a result of an intracranial hemorrhage related to herpes encephalitis.

METHODS

The patient's performance on several linguistic tasks carried out in the first language (Arabic) and in the second language (Hebrew) was assessed, and his performance in the two languages was compared.

RESULTS

The patient displayed somewhat different symptomatologies in the two languages. The results revealed dissociation between the two languages in terms of both the types and the magnitude of errors, pointing to aphasic symptoms in both languages, with Hebrew being the more impaired. Further analysis disclosed that this dissociation was apparently caused not by damage to his semantic system, but rather by damage at the lexical level.

CONCLUSION

The results suggest that the principles governing the organization of lexical representations in the brain are not similar for the two languages.

Temporal characteristics of semantic perseverations induced by blocked-cyclic picture naming

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 category. Evidence suggests that the temporal properties of these "semantic perseverations" may differ from typical lexical perseverations in aphasia. To explore this, we studied semantic perseverations generated by participants with aphasia on a naming task with 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 properties of these perseverations were investigated by analyzing how often they occurred at each lag (distance from prior occurrence) and how time (response-stimulus interval) influenced the lag function. Chance data sets were created by re-shuffling stimulus-response pairs in a manner that preserved unique features of the blocking design. We found that the semantic blocking manipulation did not eliminate the expected bias for short-lag perseverations (recency bias). However, immediate (lag 1) perseverations were not invariably the most frequent, which hints at a source of inconsistency within and across studies. Importantly, there was not a reliable difference between the lag functions for perseverations generated with a 5s, compared to 1s, response-stimulus interval. The combination of recency bias 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.

Semantic memory is key to binding phonology: converging evidence from immediate serial recall in semantic dementia and healthy participants

Patients with semantic dementia (SD) make numerous phoneme migration errors when recalling lists of words they no longer fully understand, suggesting that word meaning makes a critical contribution to phoneme binding in verbal short-term memory. Healthy individuals make errors that appear similar when recalling lists of nonwords, which also lack semantic support. Although previous studies have assumed that the errors in these two groups stem from the same underlying cause, they have never been directly compared. We tackled this issue by examining immediate serial recall for SD patients and controls on "pure" word lists and "mixed" lists that contained a mixture of words and nonwords. SD patients were equally poor at pure and mixed lists and made numerous phoneme migration errors in both conditions. In contrast, controls recalled pure lists better than mixed lists and only produced phoneme migrations for mixed lists. We also examined the claim that semantic activation is critical for words in the primacy portion of the list. In fact, the effect of mixed lists was greatest for later serial positions in the control group and in the SD group recall was poorest towards the ends of lists. These results suggest that mixing nonwords with words in healthy participants closely mimics the impact of semantic degradation in SD on word list recall. The study provides converging evidence for the idea that lexical/semantic knowledge is an important source of constraint on phonological coherence, ensuring that phonemes in familiar words are bound to each other and emerge together in recall.

Linking speech errors and phonological grammars: Insights from Harmonic Grammar networks

Phonological grammars characterize distinctions between relatively well-formed (unmarked) and relatively ill-formed (marked) phonological structures. We review evidence that markedness influences speech error probabilities. Specifically, although errors result in both unmarked as well as marked structures, there is a markedness asymmetry: errors are more likely to produce unmarked outcomes. We show that stochastic disruption to the computational mechanisms realizing a Harmonic Grammar (HG) can account for the broad empirical patterns of speech errors. We demonstrate that our proposal can account for the general markedness asymmetry. We also develop methods for linking particular HG proposals to speech error distributions, and illustrate these methods using a simple HG and a set of initial consonant errors in English.

Typicality of inanimate category exemplars in aphasia treatment: further evidence for semantic complexity

PURPOSE

The typicality treatment approach on improving naming was investigated within 2 inanimate categories (furniture and clothing) using a single-subject experimental design across participants and behaviors in 5 patients with aphasia.

METHOD

Participants received a semantic feature treatment to improve naming of either typical or atypical items within semantic categories, whereas generalization was tested to untrained items of the category. The order of typicality and category trained was counterbalanced across participants.

RESULTS

Results indicated that 2 out of 4 patients trained on naming of atypical examples demonstrated generalization to naming untrained typical examples. One patient showed trends toward generalization but did not achieve criterion. Furthermore, all 4 patients trained on typical examples demonstrated no generalized naming to untrained atypical examples within the category. Also, analysis of errors indicated an evolution of errors as a result of treatment, from those with no apparent relationship to the target to primarily semantic and phonemic paraphasias.

CONCLUSION

These results extend our previous findings (S. Kiran & C. K. Thompson, 2003a) to patients with nonfluent aphasia and to inanimate categories such as furniture and clothing. Additionally, the results provide support for the claim that training atypical examples is a more efficient method of facilitating generalization to untrained items within a category than training typical examples (S. Kiran, 2007).

Are phonological influences on lexical (mis)selection the result of a monitoring bias?

A monitoring bias account is often used to explain speech error patterns that seem to be the result of an interactive language production system, like phonological influences on lexical selection errors. A biased monitor is suggested to detect and covertly correct certain errors more often than others. For instance, this account predicts that errors that are phonologically similar to intended words are harder to detect than those that are phonologically dissimilar. To test this, we tried to elicit phonological errors under the same conditions as those that show other kinds of lexical selection errors. In five experiments, we presented participants with high cloze probability sentence fragments followed by a picture that was semantically related, a homophone of a semantically related word, or phonologically related to the (implicit) last word of the sentence. All experiments elicited semantic completions or homophones of semantic completions, but none elicited phonological completions. This finding is hard to reconcile with a monitoring bias account and is better explained with an interactive production system. Additionally, this finding constrains the amount of bottom-up information flow in interactive models.

Semantic complexity in treatment of naming deficits in aphasia: evidence from well-defined categories

PURPOSE

Our previous work on manipulating typicality of category exemplars during treatment of naming deficits has shown that training atypical examples generalizes to untrained typical examples but not vice versa. In contrast to natural categories that consist of fuzzy boundaries, well-defined categories (e.g., shapes) have rigid category boundaries. Whether these categories illustrate typicality effects similar to natural categories is under debate. The present study addressed this question in the context of treatment for naming deficits in aphasia.

METHODS

Using a single-subject experiment design, 3 participants with aphasia received a semantic feature treatment to improve naming of either typical or atypical items of shapes, while generalization was tested to untrained items of the category.

RESULTS

For 2 of the 3 participants, training naming of atypical examples of shapes resulted in improved naming of untrained typical examples. Training typical examples in 1 participant did not improve naming of atypical examples. All 3 participants, however, showed weak acquisition trends.

CONCLUSIONS

Results of the present study show equivocal support for manipulating typicality as a treatment variable within well-defined categories. Instead, these results indicate that acquisition and generalization effects within well-defined categories such as shapes are overshadowed by their inherent abstractness.

Performance in L1 and L2 observed in Arabic-Hebrew bilingual aphasic following brain tumor: A case constitutes double dissociation

This study aimed to verify the existence of a double first language (L1)/second language (L2) dissociation. In recent work, I described a case study of a Arabic-Hebrew aphasic patient (MH) with disturbances in the two languages, with Hebrew (L2) being more impaired. In this case, an Arabic-Hebrew bilingual patient (MM) with a similar cultural background who suffered brain damage following a left hemisphere tumor (oligodendroglioma) and craniotomy is reported. The same materials were used, which overcame methodological constraints in our previous work. The results revealed a complementary pattern of severe impairment of L1 (Arabic), while MM had mild language disorder in L2 (Hebrew) with intact semantic knowledge in both languages. These two cases demonstrate a double L1/L2 dissociation in unique languages, and support the notion that bilingual persons could have distinct cortical language areas.

The left posterior superior temporal gyrus participates specifically in accessing lexical phonology

Impairments in phonological processing have been associated with damage to the region of the left posterior superior temporal gyrus (pSTG), but the extent to which this area supports phonological processing, independent of semantic processing, is less clear. We used repetition priming and neural repetition suppression during functional magnetic resonance imaging (fMRI) in an auditory pseudoword repetition task as a semantics-free model of lexical (whole-word) phonological access. Across six repetitions, we observed repetition priming in terms of decreased reaction time and repetition suppression in terms of reduced neural activity. An additional analysis aimed at sublexical phonology did not show significant effects in the areas where repetition suppression was observed. To test if these areas were relevant to real word production, we performed a conjunction analysis with data from a separate fMRI experiment which manipulated word frequency (a putative index of lexical phonological access) in picture naming. The left pSTG demonstrated significant effects independently in both experiments, suggesting that this area participates specifically in accessing lexical phonology.

Computational modelling of phonological dyslexia: how does the DRC model fare?

This paper investigates the patterns of reading impairment in phonological dyslexia using computational modelling with the dual-route cascaded model of reading (DRC, Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001). Systematic lesioning of nonlexical and phonological processes in DRC demonstrates that different lesions and severity of those lesions can reproduce features of phonological dyslexia including impaired reading of nonwords, relatively spared reading of words, an advantage for reading pseudohomophones. Using the same stimuli for model and for patients, lesions to DRC were also used to simulate the reading accuracy shown by three individuals with acquired phonological dyslexia. No single lesion could replicate the reading performance of all three individuals. In order to simulate reading accuracy for one individual a phonological impairment was necessary (addition of noise to the phoneme units), and for the remaining two individuals an impairment to nonlexical reading procedures (increasing the time interval between each new letter being processed) was necessary. We argue that no single locus of impairment (neither phonological nor nonlexical) can account for the reading impairments of all individuals with phonological dyslexia. Instead, different individuals have different impairments (and combinations of impairments) that together provide the spectrum of patterns found in phonological dyslexia.

The many places of frequency: evidence for a novel locus of the lexical frequency effect in word production

The effect of lexical frequency on language-processing tasks is exceptionally reliable. For example, pictures with higher frequency names are named faster and more accurately than those with lower frequency names. Experiments with normal participants and patients strongly suggest that this production effect arises at the level of lexical access. Further work has suggested that within lexical access this effect arises at the level of lexical representations. Here we present patient E.C. who shows an effect of lexical frequency on his nonword error rate. The best explanation of his performance is that there is an additional locus of frequency at the interface of lexical and segmental representational levels. We confirm this hypothesis by showing that only computational models with frequency at this new locus can produce a similar error pattern to that of patient E.C. Finally, in an analysis of a large group of Italian patients, we show that there exist patients who replicate E.C.'s pattern of results and others who show the complementary pattern of frequency effects on semantic error rates. Our results combined with previous findings suggest that frequency plays a role throughout the process of lexical access.

Bilingual deep dysphasia

We report B.R.B., a bilingual Turkish-English speaker with deep dysphasia. B.R.B. shows the typical pattern of semantic errors in repetition with effects of lexicality and imageability on performance in both languages. The question we asked is whether language type (Turkish or English) or language status--that is, first acquired (L1) or second acquired (L2)--has a greater impact on performance. Results showed that repetition in L1 (Turkish) was better than that in L2 (English). We also observed effects of language status on oral reading, writing to dictation, and naming (spoken and written) with greater impairment to repetition than other tasks in both languages. An additional finding was that spoken-word translation in both directions was worse than written-word translation, and word class had an effect on translation from L1 to L2. We argue that interactive activation models of deep dysphasia could explain deep dysphasia in bilingual speakers and interactions between task and language, if the weighted connections that support language processing in L2 are assumed to be weaker, thus causing rapid phonological decay to have more impact on task performance in L2. Implications of the results for models of bilingual language processing are also considered.

Phonotactic probability effects in children who stutter

PURPOSE

The purpose of this study was to examine the influence of phonotactic probability, which is the frequency of different sound segments and segment sequences, on the overall fluency with which words are produced by preschool children who stutter (CWS) as well as to determine whether it has an effect on the type of stuttered disfluency produced.

METHOD

A 500+ word language sample was obtained from 19 CWS. Each stuttered word was randomly paired with a fluently produced word that closely matched it in grammatical class, word length, familiarity, word and neighborhood frequency, and neighborhood density. Phonotactic probability values were obtained for the stuttered and fluent words from an online database.

RESULTS

Phonotactic probability did not have a significant influence on the overall susceptibility of words to stuttering, but it did impact the type of stuttered disfluency produced. In specific, single-syllable word repetitions were significantly lower in phonotactic probability than fluently produced words, part-word repetitions, and sound prolongations.

CONCLUSIONS

In general, the differential impact of phonotactic probability on the type of stuttering-like disfluency produced by young CWS provides some support for the notion that different disfluency types may originate in the disruption of different levels of processing.

A patient with phonologic alexia can learn to read "much" from "mud pies"

People with phonologic alexia often have difficulty reading functors and verbs, in addition to pseudowords. Friedman et al. [Friedman, R. B., Sample, D. M, & Lott, S. N. (2002). The role of level of representation in the use of paired associate learning for rehabilitation of alexia. Neuropsychologia, 40, 223-234] reported a successful treatment for phonologic alexia that paired problematic functors and verbs with easily read relays that were homophonous nouns (e.g. "be" paired with "bee"). The current study evaluates the efficacy of pairing problematic grammatical words with relays that share initial phonemes, but vary in the relationship of their final phonemes. Results showed that reading of target grammatical words improved to criterion level (90% accuracy over two consecutive probes) in all experimental conditions with shared phonology, but remained far below criterion level in control conditions. There was a significant correlation between degree of phonologic relatedness and error rate. Maintenance of the treatment effect was poor as assessed by traditional measurement, however a dramatic savings during relearning was demonstrated during a subsequent treatment phase. The finding that reading can be re-organized by pairing target words not only with homophones, but with other phonologically related relays, suggests that this approach could be applied to a wide corpus of words and, therefore, potentially be of great use clinically. We suggest, within a connectionist account, that the treatment effect results from relays priming the initial phonologic units of the targets.

Does language guide event perception? Evidence from eye movements

Languages differ in how they encode motion. When describing bounded motion, English speakers typically use verbs that convey information about manner (e.g., slide, skip, walk) rather than path (e.g., approach, ascend), whereas Greek speakers do the opposite. We investigated whether this strong cross-language difference influences how people allocate attention during motion perception. We compared eye movements from Greek and English speakers as they viewed motion events while (a) preparing verbal descriptions or (b) memorizing the events. During the verbal description task, speakers' eyes rapidly focused on the event components typically encoded in their native language, generating significant cross-language differences even during the first second of motion onset. However, when freely inspecting ongoing events, as in the memorization task, people allocated attention similarly regardless of the language they speak. Differences between language groups arose only after the motion stopped, such that participants spontaneously studied those aspects of the scene that their language does not routinely encode in verbs. These findings offer a novel perspective on the relation between language and perceptual/cognitive processes. They indicate that attention allocation during event perception is not affected by the perceiver's native language; effects of language arise only when linguistic forms are recruited to achieve the task, such as when committing facts to memory.

Where is the effect of frequency in word production? Insights from aphasic picture-naming errors

Some theories of lexical access in production locate the effect of lexical frequency at the retrieval of a word's phonological characteristics, as opposed to the prior retrieval of a holistic representation of the word from its meaning. Yet there is evidence from both normal and aphasic individuals that frequency may influence both of these retrieval processes. This inconsistency is especially relevant in light of recent attempts to determine the representation of another lexical property--age of acquisition or AoA--whose effect is similar to that of frequency. To further explore the representations of these lexical variables in the word retrieval system, we performed hierarchical, multinomial logistic regression analyses of 50 aphasic patients' picture-naming responses. While both log frequency and AoA had a significant influence on patient accuracy and led to fewer phonologically related errors and omissions, only log frequency had an effect on semantically related errors. These results provide evidence for a lexical access process sensitive to frequency at all stages, but with AoA having a more limited effect.

Aphasia therapy on a neuroscience basis

BACKGROUND: Brain research has documented that the cortical mechanisms for language and action are tightly interwoven and, concurrently, new approaches to language therapy in neurological patients are being developed that implement language training in the context of relevant linguistic and non-linguistic actions, therefore taking advantage of the mutual connections of language and action systems in the brain. A further well-known neuroscience principle is that learning at the neuronal level is driven by correlation; consequently, new approaches to language therapy emphasise massed practice in a short time, thus maximising therapy quantity and frequency and, therefore, correlation at the behavioural and neuronal levels. Learned non-use of unsuccessful actions plays a major role in the chronification of neurological deficits, and behavioural approaches to therapy have therefore employed shaping and other learning techniques to counteract such non-use. AIMS: Advances in theoretical and experimental neuroscience have important implications for clinical practice. We exemplify this in the domain of aphasia rehabilitation. MAIN CONTRIBUTION: Whereas classical wisdom had been that aphasia cannot be significantly improved at a chronic stage, we here review evidence that one type of intensive language-action therapy (ILAT)-constraint-induced aphasia therapy-led to significant improvement of language performance in patients with chronic aphasia. We discuss perspectives for further improving speech-language therapy, including drug treatment that may be particularly fruitful when applied in conjunction with behavioural treatment. In a final section we highlight intensive and rapid therapy studies in chronic aphasia as a unique tool for exploring the cortical reorganisation of language. CONCLUSIONS: We conclude that intensive language action therapy is an efficient tool for improving language functions even at chronic stages of aphasia. Therapy studies using this technique can open new perspectives for research into the plasticity of human language circuits.

Saying the right word at the right time: Syntagmatic and paradigmatic interference in sentence production

Retrieving a word in a sentence requires speakers to overcome syntagmatic, as well as paradigmatic interference. When accessing cat in "The cat chased the string," not only are similar competitors such as dog and cap activated, but also other words in the planned sentence, such as chase and string. We hypothesize that both types of interference impact the same stage of lexical access, and review connectionist models of production that use an error-driven learning algorithm to overcome that interference. This learning algorithm creates a mechanism that limits syntagmatic interference, the syntactic "traffic cop," a configuration of excitatory and inhibitory connections from syntactic-sequential states to lexical units. We relate the models to word and sentence production data, from both normal and aphasic speakers.

Age of acquisition and repetition priming effects on picture naming of children who do and do not stutter

The effects of age of acquisition and repetition priming on picture naming latencies and errors were studied in 22 children who stutter (CWS) and 22 children who do not stutter (CWNS) between the ages of 3;1 and 5;7. Children participated in a computerized picture naming task where they named pictures of both early and late acquired (AoA) words in two consecutive stages. Findings revealed that all children's picture naming latencies and errors were reduced following repetition priming and in response to early AoA words relative to late AoA words. AoA and repetition priming effects were similar for children in both talker groups, with one exception. Namely, CWS benefitted significantly more, in terms of error reduction, than CWNS from repetition priming for late AoA words. In addition, CWNS exhibited a significant, positive association between linguistic speed and measures of vocabulary, but CWS did not. These findings were taken to suggest that the (a) semantic-phonological connections of CWS may not be as strong as those of CWNS, and (b) existing lexical measures may not be sensitive enough to differentiate CWS from CWNS in lexically related aspects of language production.

EDUCATIONAL OBJECTIVES

After reading this article, the learner will be able to: (a) describe the effects of repetition priming and age of word acquisition in speech production; (b) summarize the performance similarities and differences of children who stutter and children who do not stutter on a computerized picture naming task; and (c) compare the results of the present study with previous work in this area.

The Search for the Phonological Store: From Loop to Convolution

The phonological loop system of Baddeley and colleagues' Working Memory model is a major accomplishment of the modern era of cognitive psychology. It was one of the first information processing models to make an explicit attempt to accommodate both traditional behavioral data and the results of neuropsychological case studies in an integrated theoretical framework. In the early and middle 1990s, the purview of the phonological loop was expanded to include the emerging field of functional brain imaging. The modular and componential structure of the phonological loop seemed to disclose a structure that might well be transcribed, intact, onto the convolutions of the brain. It was the phonological store component, however, with its simple and modular quality, that most appealed to the neuroimaging field as the psychological “box” that might most plausibly be located in the brain. Functional neuroimaging studies initially designated regions in the parietal cortex as constituting the “neural correlate” of the phonological store, whereas later studies pointed to regions in the posterior temporal cortex. In this review, however, we argue the phonological store as a theoretical construct does not precisely correspond to a single, functionally discrete, brain region. Rather, converging evidence from neurology, cognitive psychology, and functional neuroimaging argue for a reconceptualization of phonological short-term memory as emerging from the integrated action of the neural processes that underlie the perception and production of speech.

A psychometric analysis of functional category production in English agrammatic narratives

Hierarchical models of agrammatism propose that sentence production deficits can be accounted for in terms of clausal syntactic structure [Friedmann, N., & Grodzinsky, Y. (1997). Tense and agreement in agrammatic production: Pruning the syntactic tree. Brain and Language, 56, 397-425; Hagiwara, H. (1995). The breakdown of functional categories and the economy of derivation. Brain and Language, 50, 92-116]. Such theories predict that morpho-syntactic elements associated with higher nodes in the syntactic tree (complementizers and verb inflections) will be more impaired than elements associated with lower structural positions (negation markers and aspectual verb forms). While this hypothesis has been supported by the results of several studies [Benedet, M. J., Christiansen, J. A., & Goodglass, H. (1998). A cross-linguistic study of grammatical morphology in Spanish- and English-speaking agrammatic patients. Cortex, 34, 309-336; Friedmann, N. (2001). Agrammatism and the psychological reality of the syntactic tree. Journal of Psycholinguistic Research, 30, 71-88; Friedmann, N. (2002). Question production in agrammatism: The tree pruning hypothesis. Brain and Language, 80, 160-187], it has also been challenged on several grounds [Burchert, F., Swoboda-Moll, M., & De Bleser, R. (2005a). Tense and agreement dissociations in German agrammatic speakers: Underspecification vs. hierarchy. Brain and Language, 94, 188-199; Lee, M. (2003). Dissociations among functional categories in Korean agrammatism. Brain and Language, 84, 170-188; Lee, J., Milman, L. H., & Thompson, C. K. (2005). Functional category production in agrammatic speech. Brain and Language, 95, 123-124]. In this paper the question of hierarchical structure was re-examined within the framework of Item Response Theory [IRT, Rasch, G. (1980). Probabilistic models for some intelligence and attainment tests (Expanded ed.). Chicago: University of Chicago Press]. IRT is a probabilistic model widely used in the field of psychometrics to model behavioral constructs as numeric variables. In this study we examined production of functional categories (complementizers, verb inflections, negation markers, and aspectual verb forms) in narrative samples elicited from 18 individuals diagnosed with nonfluent aphasia and 18 matched controls. Data from the aphasic participants were entered into an IRT analysis to test (1) whether production of clausal functional categories can be represented as a variable on a numeric scale; and (2) whether production patterns were consistent with hierarchical syntactic structure. Pearson r correlation coefficients were also computed to determine whether there was a relation between functional category production and other indices of language performance. Results indicate that functional category production can be modeled as a numeric variable using IRT. Furthermore, although variability was observed across individuals, consistent patterns were evident when the data were interpreted within a probabilistic framework. Although functional category production was moderately correlated with a second measure of clausal structure (clause length), it was not correlated with more distant language constructs (noun/verb ratio and WAB A.Q.). These results suggest that functional category production is related to some, but not all, measures of agrammatic language performance.

A link between neuroscience and informatics: large-scale modeling of memory processes

Utilizing advances in functional neuroimaging and computational neural modeling, neuroscientists have increasingly sought to investigate how distributed networks, composed of functionally defined subregions, combine to produce cognition. Large-scale, biologically realistic neural models, which integrate data from cellular, regional, whole brain, and behavioral sources, delineate specific hypotheses about how these interacting neural populations might carry out high-level cognitive tasks. In this review, we discuss neuroimaging, neural modeling, and the utility of large-scale biologically realistic models using modeling of short-term memory as an example. We present a sketch of the data regarding the neural basis of short-term memory from non-human electrophysiological, computational and neuroimaging perspectives, highlighting the multiple interacting brain regions believed to be involved. Through a review of several efforts, including our own, to combine neural modeling and neuroimaging data, we argue that large scale neural models provide specific advantages in understanding the distributed networks underlying cognition and behavior.

Typicality Treatment for Naming Deficits in Aphasia: Why Does It Work?

Purpose: The present paper provides a review of a recent treatment approach for alleviating naming deficits in patients with aphasia. This is an example of a treatment that is theoretically based and supported by behavioral evidence from normal adult language processing.

Method: First, a theoretical basis for naming deficits in patients with aphasia is provided. Then, current options for semantic-based treatment of naming deficits are reviewed. Previous work from our laboratory indicates that training atypical examples of semantic categories resulted in generalization to untrained typical examples, whereas training typical examples did not result in generalization to untrained atypical examples.

The usefulness of the typicality treatment approach is discussed in the context of recent studies from our laboratory that have examined this approach across a variety of semantic categories, including animate categories (e.g., birds), inanimate categories (e.g., furniture), well-defined categories such as “shapes,” and goal derived categories such as “things to have in a garage sale.”

Conclusions: We suggest that the success of the treatment seemingly relies on the stringent selection of typical/atypical examples and on highlighting the variation of semantic features of the trained category as part of the treatment protocol.

Evaluating the effectiveness of semantic-based treatment for naming deficits in aphasia: what works?

This article reviews the basic principles and evidence for the effectiveness of a semantic-based treatment for naming deficits in aphasia. This article focuses on three aspects of semantic-based treatment. First, the theoretical basis for semantic treatment approaches to alleviate naming deficits is explained. Second, the different types of semantic treatment approaches (i.e., substitutive and restitutive treatments) are reviewed. More attention is provided to restitutive treatment approaches, and some ideas regarding why these treatments may be effective are discussed. We argue that strengthening access to impaired semantic and phonologic representations and facilitating generalization to untrained but related targets are two factors determining the success of a restitutive-based semantic treatment. Finally, in the third section of the article, the effect of semantic treatment on the overall communicative effectiveness and suggestions for future research in this field are discussed.

Translational research in aphasia: from neuroscience to neurorehabilitation

PURPOSE

In this article, the authors encapsulate discussions of the Language Work Group that took place as part of the Workshop in Plasticity/NeuroRehabilitation Research at the University of Florida in April 2005.

METHOD

In this narrative review, they define neuroplasticity and review studies that demonstrate neural changes associated with aphasia recovery and treatment. The authors then summarize basic science evidence from animals, human cognition, and computational neuroscience that is relevant to aphasia treatment research. They then turn to the aphasia treatment literature in which evidence exists to support several of the neuroscience principles.

CONCLUSION

Despite the extant aphasia treatment literature, many questions remain regarding how neuroscience principles can be manipulated to maximize aphasia recovery and treatment. They propose a framework, incorporating some of these principles, that may serve as a potential roadmap for future investigations of aphasia treatment and recovery. In addition to translational investigations from basic to clinical science, the authors propose several areas in which translation can occur from clinical to basic science to contribute to the fundamental knowledge base of neurorehabilitation. This article is intended to reinvigorate interest in delineating the factors influencing successful recovery from aphasia through basic, translational, and clinical research.

Deficits of knowledge versus executive control in semantic cognition: insights from cued naming

Deficits of semantic cognition in semantic dementia and in aphasia consequent on CVA (stroke) are qualitatively different. Patients with semantic dementia are characterised by progressive degradation of central semantic representations, whereas multimodal semantic deficits in stroke aphasia reflect impairment of executive processes that help to direct and control semantic activation in a task-appropriate fashion [Jefferies, E., & Lambon Ralph, M. A. (2006). Semantic impairment in stroke aphasia vs. semantic dementia: A case-series comparison. Brain 129, 2132-2147]. We explored interactions between these two aspects of semantic cognition by examining the effects of cumulative phonemic cueing on picture naming in case series of these two types of patient. The stroke aphasic patients with multimodal semantic deficits cued very readily and demonstrated near-perfect name retrieval when cumulative phonemic cues reached or exceeded the target name's uniqueness point. Therefore, knowledge of the picture names was largely intact for the aphasic patients, but they were unable to retrieve this information without cues that helped to direct activation towards the target response. Equivalent phonemic cues engendered significant but much more limited benefit to the semantic dementia patients: their naming was still severely impaired even when most of the word had been provided. In contrast to the pattern in the stroke aphasia group, successful cueing was mainly confined to the more familiar un-named pictures. We propose that this limited cueing effect in semantic dementia follows from the fact that concepts deteriorate in a graded fashion [Rogers, T. T., Lambon Ralph, M. A., Garrard, P., Bozeat, S., McClelland, J. L., & Hodges, J. R., et al. (2004). The structure and deterioration of semantic memory: A neuropsychological and computational investigation. Psychological Review 111, 205-235]. For partially degraded items, the residual conceptual knowledge may be insufficient to drive speech production to completion but these items might reach threshold when they are bolstered by cues.

Omissions and semantic errors in aphasic naming: is there a link?

Within a discrete two-stage model of lexicalization, semantic errors and errors of omission are assumed to be independent events. In contrast, cascading and interactive models allow for an influence of word form on lexical selection and thus for an inherent relationship in accounting for both error types. A group of 17 aphasic patients was assessed with a naming test controlling for semantic competition of the target items. Semantic errors were more frequent for targets with many competitors than for targets with few competitors while omissions were more frequent when few competitors were available. However, the overall sums of errors in both item groups were comparable. These results imply a common source of both error types and thus speak against a strictly serial model of naming.

Episodic and semantic memory influences on picture naming in Alzheimer's disease

This study investigated the relationship between semantic and episodic memory as they support lexical access by healthy younger and older adults and individuals with Alzheimer's disease (AD). In particular, we were interested in examining the pattern of semantic and episodic memory declines in AD (i.e., word-finding difficulty and impaired recent memory) vis-à-vis more preserved remote memories. We administered a picture naming task in which the episodic period of the pictures and whether the pictured items were unique to one period or commonly used across periods were varied. Groups of younger adults (N=40), healthy older adults (N=20) and older adults with AD (N=18) were asked to name drawings of objects in four conditions: dated unique, contemporary unique, dated common, and contemporary common. The results indicated that all participants named items that were common to both episodic periods more successfully than items unique to one period. An interaction was observed such that the healthy older and AD groups were more successful in retrieving names of objects presented in the dated compared to contemporary unique conditions, whereas the younger adults showed the reverse pattern. These results indicate that naming ability is affected both by the cumulative frequency of using an item over a lifetime and by when an item was first acquired. The findings support a theoretical stance which proposes an enduring reciprocal link between semantic and episodic memory. This theoretical relationship has practical implications for the development of intervention strategies when interacting with persons who have AD.

Mimicking aphasic semantic errors in normal speech production: evidence from a novel experimental paradigm

Semantic errors are commonly found in semantic dementia (SD) and some forms of stroke aphasia and provide insights into semantic processing and speech production. Low error rates are found in standard picture naming tasks in normal controls. In order to increase error rates and thus provide an experimental model of aphasic performance, this study utilised a novel method- tempo picture naming. Experiment 1 showed that, compared to standard deadline naming tasks, participants made more errors on the tempo picture naming tasks. Further, RTs were longer and more errors were produced to living items than non-living items a pattern seen in both semantic dementia and semantically-impaired stroke aphasic patients. Experiment 2 showed that providing the initial phoneme as a cue enhanced performance whereas providing an incorrect phonemic cue further reduced performance. These results support the contention that the tempo picture naming paradigm reduces the time allowed for controlled semantic processing causing increased error rates. This experimental procedure would, therefore, appear to mimic the performance of aphasic patients with multi-modal semantic impairment that results from poor semantic control rather than the degradation of semantic representations observed in semantic dementia [Jefferies, E. A., & Lambon Ralph, M. A. (2006). Semantic impairment in stoke aphasia vs. semantic dementia: A case-series comparison. Brain, 129, 2132-2147]. Further implications for theories of semantic cognition and models of speech processing are discussed.

Effects of verb complexity on speech errors

Two experiments examined whether semantically related verbs that contrast with respect to the absence versus the presence of an additional semantic feature differentially compete for selection during the encoding of a sentence for production. In both experiments, a speech error induction task was used to elicit contextual (misordering) errors involving semantically related verbs that contrasted only in their semantic complexity or in both their semantic and morphophonological complexity. The prediction was that an asymmetry in contextual errors would be observed in which the more complex verbs would replace the simpler verbs more often than the reverse. This prediction was confirmed in both experiments, with more perseverations and anticipations involving the semantically more complex verb of antonym pairs in Experiment 1, and more perseverations and anticipations involving the semantically more-specified verb of a heavy-light pair in Experiment 2. The implications of the results for spreading-activation theories of language production are discussed.

Stress assignment in aphasia: word and non-word reading and non-word repetition

This paper investigates stress assignment in Dutch aphasic patients in non-word repetition, as well as in real-word and non-word reading. Performance on the non-word reading task was similar for the aphasic patients and the control group, as mainly regular stress was assigned to the targets. However, there were group differences on the real-word reading and non-word repetition tasks. Unlike the non-brain-damaged group, the patients showed a strong regularization tendency in their repetition of irregular patterns. The patients' stress error patterns suggest an impairment in retention or retrieval of targets with irregular stress patterns. Limited verbal short-term memory is proposed as a possible underlying cause for the stress difficulties.

A neural signature of phonological access: distinguishing the effects of word frequency from familiarity and length in overt picture naming

Cognitive models of word production correlate the word frequency effect (i.e., the fact that words which appear with less frequency take longer to produce) with an increased processing cost to activate the whole-word (lexical) phonological representation. We performed functional magnetic resonance imaging (fMRI) while subjects produced overt naming responses to photographs of animals and manipulable objects that had high name agreement but were of varying frequency, with the purpose of identifying neural structures participating specifically in activating whole-word phonological representations, as opposed to activating lexical semantic representations or articulatory-motor routines. Blood oxygen level-dependent responses were analyzed using a parametric approach based on the frequency with which each word produced appears in the language. Parallel analyses were performed for concept familiarity and word length, which provided indices of semantic and articulatory loads. These analyses permitted us to identify regions related to word frequency alone, and therefore, likely to be related specifically to activation of phonological word forms. We hypothesized that the increased processing cost of producing lower-frequency words would correlate with activation of the left posterior inferotemporal (IT) cortex, the left posterior superior temporal gyrus (pSTG), and the left inferior frontal gyrus (IFG). Scan-time response latencies demonstrated the expected word frequency effect. Analysis of the fMRI data revealed that activity in the pSTG was modulated by frequency but not word length or concept familiarity. In contrast, parts of IT and IFG demonstrated conjoint frequency and familiarity effects, and parts of both primary motor regions demonstrated conjoint effects of frequency and word length. The results are consistent with a model of word production in which lexical-semantic and lexical-phonological information are accessed by overlapping neural systems within posterior and anterior language-related cortices, with pSTG specifically involved in accessing lexical phonology.

Neural correlates of phonological and semantic-based anomia treatment in aphasia

Most naming treatments in aphasia either assume a phonological or semantic emphasis or a combination thereof. However, it is unclear whether semantic or phonological treatments recruit the same or different cortical areas in chronic aphasia. Employing three persons with aphasia, two of whom were non-fluent, the present study compared changes in neural recruitment associated with phonologic and semantic-based naming treatments. The participants with non-fluent aphasia were able to name more items following both treatment approaches. Although this was not the case for the participant who had fluent aphasia, her naming errors decreased considerably following treatment. Post-treatment fMRI revealed similar changes in neural activity bilaterally in the precuneus among the two non-fluent participants--increased activity was noted in the right entorhinal cortex and posterior thalamus on post-treatment scans for the third participant. These findings imply that cortical areas not traditionally related to language processing may support anomia recovery in some patients with chronic aphasia.