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.

A neurophysiological study of semantic processing in Parkinson’s disease

Objectives: Cognitive-linguistic impairments in Parkinson's disease (PD) have been well documented; however, few studies have explored the neurophysiological underpinnings of semantic deficits in PD. This study investigated semantic function in PD using event-related potentials. Methods: Eighteen people with PD and 18 healthy controls performed a semantic judgement task on written word pairs that were either congruent or incongruent. Results: The mean amplitude of the N400 for new incongruent word pairs was similar for both groups, however the onset latency was delayed in the PD group. Further analysis of the data revealed that both groups demonstrated attenuation of the N400 for repeated incongruent trials, as well as attenuation of the P600 component for repeated congruent trials. Conclusions: The presence of N400 congruity and N400 repetition effects in the PD group suggests that semantic processing is generally intact, but with a slower time course as evidenced by the delayed N400. Additional research will be required to determine whether N400 and P600 repetition effects are sensitive to further cognitive decline in PD

The Suppression of Irrelevant Semantic Representations in Parkinson’s Disease

The impairment of lexical-semantic inhibition mechanisms in Parkinson’s disease (PD) remains a source of contention. In order to observe whether people with PD are able to suppress irrelevant semantic information during picture naming, the present study employed an object-based negative priming paradigm with 16 participants with PD and 13 healthy controls. The task required participants to name a red target image while ignoring a superimposed, green distractor image. The semantic relationship between the distractor image and the target image of the subsequent trial was manipulated, such that the distractor image was identical, semantically related, or semantically unrelated to said target image. The PD group and the control group were slower in naming a target image that had previously served as a distractor image, relative to naming a target image that was unrelated to the previous distractor image. Thus, a negative priming effect was present in both groups. Furthermore, no significant difference in the magnitude of this effect was observed between the control and PD groups. When considered in the context of existing literature surrounding negative priming in PD, these results suggest that inhibition is subserved by multiple, domain-specific mechanisms and that the inhibitory processing of visual-semantic stimuli is intact in PD

Priming Picture Naming with a Semantic Task: An fMRI Investigation

Prior semantic processing can enhance subsequent picture naming performance, yet the neurocognitive mechanisms underlying this effect and its longevity are unknown. This functional magnetic resonance imaging study examined whether different neurological mechanisms underlie short-term (within minutes) and long-term (within days) facilitation effects from a semantic task in healthy older adults. Both short- and long-term facilitated items were named significantly faster than unfacilitated items, with short-term items significantly faster than long-term items. Region of interest results identified decreased activity for long-term facilitated items compared to unfacilitated and short-term facilitated items in the mid-portion of the middle temporal gyrus, indicating lexical-semantic priming. Additionally, in the whole brain results, increased activity for short-term facilitated items was identified in regions previously linked to episodic memory and object recognition, including the right lingual gyrus (extending to the precuneus region) and the left inferior occipital gyrus (extending to the left fusiform region). These findings suggest that distinct neurocognitive mechanisms underlie short- and long-term facilitation of picture naming by a semantic task, with long-term effects driven by lexical-semantic priming and short-term effects by episodic memory and visual object recognition mechanisms

The neural correlates of picture naming facilitated by auditory repetition

Background: Overt repetition of auditorily presented words can facilitate picture naming performance in both unimpaired speakers and individuals with word retrieval difficulties, but the underlying neurocognitive mechanisms and longevity of such effects remain unclear. This study used functional magnetic resonance imaging to examine whether different neurological mechanisms underlie short-term (within minutes) and long-term (within days) facilitation effects from an auditory repetition task in healthy older adults

Using semantics to enhance new word learning: an ERP investigation

This study aimed to investigate whether the addition of meaning (semantics) would enhance new word learning for novel objects, and whether it would influence the neurophysiological response to new words. Twenty-five young healthy adults underwent 4 days of training to learn the names of 80 novel objects. Half of the items were learnt under a 'semantic' condition, whereby the name consisted of a legal nonword and two adjectives denoting semantic attributes. The remaining items were learnt under a 'name' condition, whereby the name consisted of a legal nonword and two proper names. Participants demonstrated superior recognition of names in the semantic condition compared to the name condition during training sessions 1-3. On the 5th day, following training, ERPs were recorded whilst participants performed a picture-word judgement task including familiar items. Analysis of the results revealed an N400 for incongruent items in the semantic condition, whilst no ERP component was observed for the name condition. These findings suggest that items learnt with semantic information form stronger associations than those trained without semantics

Spelling in children with cochlear implants: evidence of underlying processing differences

This study compared the spelling skills and sub-skills of young children with cochlear implants (CIs) who use spoken language only (n = 14) with those of a same-aged typically hearing (TH) control group (n = 30). Spelling accuracy was assessed using irregular and nonsense word stimuli. Error and regression analyses were conducted to provide insight into the phonological and orthographic spelling strategies used by each group. Results indicated that children with CIs were as accurate as the TH group. However, misspellings made by the CI group were less phonologically plausible, and while nonword spelling accuracy was related to letter-sound knowledge for the TH group, the same relationship was non-significant for the CI group. Hence, despite demonstrating a similar degree of overall spelling success to TH children, children with CIs appeared to apply phonics skills less effectively

Reading development in children with cochlear implants who communicate via spoken language: A psycholinguistic investigation

Purpose: This study sought to comprehensively examine the reading skills and subskills of children with cochlear implants (CIs) and gain insight into the processes underlying their early reading development.Method: Fourteen 6- to 9-year-old children with CIs were assessed on a range of reading and spoken language measures. Their performances were compared to a control group of 31 children with normal hearing (NH) of the same chronological and mental age. Group differences were examined using t tests and regression modeling.Results: Children with CIs performed significantly worse than children with NH on reading accuracy, phonological processing, and spoken language tasks. The predominant predictor of reading comprehension was word reading accuracy for the CI group and listening comprehension for the NH group. Word reading profiles were similar across groups, with orthographic and phonological processing skills both contributing significant variance.Conclusions: Children with CIs demonstrated more early reading difficulties than their peers with NH. As predicted by the Simple View of Reading model, successful reading comprehension for all children related to skills in listening comprehension and word recognition. The CI group's increased reliance on word reading accuracy when comprehending written text may stem from reduced word recognition automaticity. Despite showing reduced reading accuracy, children with CIs appeared to draw on orthographic and phonological skills to a similar degree as children with NH when reading words in isolation

Investigating orthographic versus auditory cross-situational word learning with online and laboratory-based testing

Research has shown that novel words can be learned through the mechanism of statistical or cross-situational word learning (CSWL). So far, CSWL studies using adult populations have focused on the presentation of spoken words. However, words can also be learned through their written form. This study compared auditory and orthographic presentations of novel words with different degrees of phonological overlap using CSWL in a laboratory-based and an online-based approach. In our analyses, we first compared accuracy across modalities, with our findings showing more accurate recognition performance for CSWL when novel words were presented through their written forms (orthographic condition) rather than through their spoken forms (auditory condition). Bayesian modeling suggested that accuracy for the orthographic condition was higher in the laboratory compared to online, whereas performance in the auditory condition was similar across both experiments. We discuss the implications of our findings for presentation modality and the benefits of our online testing protocol for future research