The basal ganglia circuits, dopamine, and ambiguous word processing: A neurobiological account of priming studies in Parkinson's disease

Research into the processing of lexical ambiguities has provided a valuable paradigm for investigating the functional architecture of the language processing system in normal and neurologically impaired populations and specifically, how basal ganglia circuits and the neurotransmitter dopamine may act to enhance and/or suppress various meanings relative to the context in which the lexical ambiguity appears. In this review, we develop the hypothesis that an integrated basal ganglia thalamocortical circuit linking the striatum and inferior frontal cortex is involved in the enhancement and suppression of ambiguous word meanings when a lexical ambiguity is presented within a linguistic context. Reference to behavioral, neurophysiological, and neurochemical studies of subcortical function in both healthy populations and people with Parkinson's disease will be used to provide further support for the proposal that the subcortex is integrally involved in ambiguous word processing. (JINS, 2008, 14, 351–364.

Post-peak fracture behavior during direct shear tests of rock joints

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Subthalamic stimulation affects homophone meaning generation in Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) in individuals with Parkinson's disease (PD) has often been associated with reduced verbal fluency performance. This study aimed to directly assess semantic switching as a function of STN stimulation in PD participants with the Homophone Meaning Generation Test (HMGT). Seventeen participants with PD who had received STN DBS completed the HMGT in on and off stimulation conditions. Twenty-one non-neurologically impaired participants acted as controls. PD participants (in both on and off stimulation conditions) generated significantly fewer meanings than control participants and consistent with the previous reports of verbal fluency impairment, PD participants produced fewer definitions in the on stimulation condition. PD participants (in both on and off stimulation conditions) also had greater difficulty generating definitions for nonhomographic homophones compared with homographic homographs. The results of this study indicate that STN stimulation exacerbates impairment in semantic switching

Semantic priming in Alzheimer's dementia

Whilst there exists general consensus in the literature that persons with dementia of the Alzheimer's type (DAT) evidence a semantic deficit, investigations to reveal the precise nature of the deficit (i.e. whether it reflects a procedural or storage deficit) have yielded equivocal results. An experimental technique used widely in the investigation of semantic processing in DAT is the semantic priming task. It has been argued that if patients with DAT are shown to perform normally on a task of automatic semantic priming, then this would argue for the structural integrity of the store of semantic memories. To date, however, the studies investigating semantic priming in DAT have described a variety of performance features with some reporting intact priming, some no priming and some exaggerated or hyperpriming. This paper reviews in detail the specific methodologies employed by the researchers investigating semantic priming in DAT in light of current theories of semantic priming. The review will outline the theoretical perspectives of semantic priming as detailed in the psycholinguistic literature on normal subjects, and then critically review the literature pertaining to semantic priming in DAT. More specifically, this paper will review the studies that have investigated attention-free semantic processing in DAT using automatic semantic priming tasks and compare their results with studies that have used, either by design or default, an attention-dependent form of semantic priming. The general weight of evidence would tend to suggest that when the experimental methodologies employed ensured only automatic activation was assessed, the DAT subjects were found to have spared semantic priming if not hyperpriming. The studies that have confounded assessment of automatic spreading activation with attention-induced priming have, without exception, demonstrated very impaired performance on the part of the DAT subjects. This pattern of results can be interpreted as reflecting significantly impaired procedural routines in DAT, with relative sparing of the structure of semantic memory

Lexical decision in Parkinson's disease: A reply to Brown, McDonald, and Spicer (1999)

Recent semantic priming investigations in Parkinsons disease (PD) employed variants of Neelys (1977) lexical decision paradigm to dissociate the automatic and attentional aspects of semantic activation (McDonald, Brown, Gorell, 1996; Spicer, Brown, Gorell, 1994). In our earlier review, we claimed that the results of Spicer, McDonald and colleagues normal control participants violated the two-process model of information processing (Posner Snyder, 1975) upon which their experimental paradigm had been based (Arnott Chenery, 1999). We argued that, even at the shortest SOA employed, key design modifications to Neelys original experiments biased the tasks employed by Spicer et al. and McDonald et al. towards being assessments of attention-dependent processes. Accordingly, we contended that experimental procedures did not speak to issues of automaticity and, therefore, Spicer, McDonald and colleagues claims of robust automatic semantic activation in PD must be treated with caution

The influence of aging and aphasia on bilingual semantic organization

Background: In managing bilingual aphasia, effective therapy techniques should be based on a clear understanding of bilingual language organization and the impact of aphasia on bilinguallexico-semantic relations. Whilst several studies have employed semantic priming to investigate the nature of bilingual semantic representation in younger adult bilinguals, few studies have investigated on-line semantic processing in older adult bilinguals or bilingual speakers with aphasia. In younger bilingual adults, evidence of cross-language priming is posited to be indicative of shared semantic representation across languages. The present study employed a bilingual semantic priming task to investigate whether cross-language priming effects would be preserved in older adult bilinguals and following neurological injury. \ud \ud Method: Twenty bilingual Italian/English speakers (13 female, 7 male) aged between 47 and 80 years (mean = 62 years) participated in the experiment. The experiment was also completed by one 70-year-old female Italian/English speaker with bilingual aphasia following a left (VA. Participants were presented with pairs of auditory stimuli in which the first stimulus was a real Italian or English word and the second stimulus was either a real word or nonword. There were four conditions in which word pairs were related: Italian-Italian, English-English, English-Italian and Italian-English and four corresponding unrelated and nonword conditions. Participants were required to make speeded lexical decisions on the second stimulus in each pair and indicated real words with a button press. No response was required for nonwords.\ud \ud Results: For the older bilingual adults, mean reaction times from the related and unrelated conditions were analysed using a linear mixed model with the within-subjects factors of relatedness, language congruence and target language and the covariate English exposure. The analysis revealed significant main effects for relatedness, language congruence and target language as well as a target language by English exposure interaction. Further pair-wise comparisons demonstrated that priming occurred in all of the within-language and cross-language conditions. This pattern was shown by participants with both less English exposure and more English exposure. In contrast, the participant with bilingual aphasia showed a reaction time advantage for related pairs only in the two within-language conditions. No such pattern was found in the cross-language conditions.\ud \ud Discussion: The results indicate that both cross-language and Within-language priming is found in older adult bilinguals which suggests that shared bilingual semantic representation is unaffected by aging mechanisms. The lack of cross-language priming, however, in the participant with bilingual aphasia suggests that neurological insult may disturb cross-language semantic connections whilst within-language semantic links appear to be preserved. The absence of cross-language priming suggests separate semantic storage for each language in the participant with aphasia.\ud \ud Conclusion: The present study results suggest that aphasia may disrupt cross-linguistic semantic connections whereas withinlanguage semantic links may be preserved. Further research is required to verify whether this pattern is consistently demonstrated in bilingual aphasia and to explore the implications for devising effective language therapy techniques

Effect of aging on learning new names and descriptions for objects

The present study consisted of two experiments to compare new word learning in healthy young (N = 11) and older (N = 17) adults within an explicit learning paradigm. Experiment 1 investigated the new name learning for familiar objects, while Experiment 2 investigated learning names and descriptions for unfamiliar objects. Participants attended five learning sessions over 5 consecutive days, during which they viewed objects with novel names with/without descriptions. The older adults were as accurate as the young adults when recalling and recognizing new names during the learning sessions. With respect to response times, the older adults were as rapid as the young adults at recognizing the new names for the familiar objects, but were slower during the follow-up sessions. The older adults were also slower when recognizing new names for unfamiliar objects. When recognizing unfamiliar object descriptions, the older adults were significantly less accurate than the young adults. These results may have implications for the treatment of acquired naming difficulties and second language learning in older adults