The meaning of tools

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When the zebra loses its stripes but is still in the savannah: results from a semantic priming paradigm in semantic dementia.

International audienceStudies using semantic priming paradigms to measure the integrity of the features underlying concepts in semantic dementia (SD) reported differential impairment, in that functional features appeared to be more robust to brain damage than other features, such as perceptual ones. However, these prior studies were single case reports and the inclusion of too many heterogeneous features under the "functional features" heading casts doubts on their apparent preservation. To verify the robustness of functional features compared with perceptual ones, we carried out a group study where we deliberately restricted the exploration of semantic features to two clearly defined types of attribute: visuoperceptual ("visual") versus contextual-functional ("contextual"). We administered an implicit lexical-decision priming task to 8 SD patients and 31 healthy matched controls, at baseline. Four of the patients underwent a follow-up assessment at one year. For controls, we found a significant priming effect in the visual condition, but not in the contextual one, whereas the SD group exhibited the reverse pattern of performances. The follow-up data provided evidence of the robustness of the dissociation between priming performances in the two attribute conditions. The fact that a particular priming effect was observed in the SD patients but not in controls could be regarded as a sign of semantic disequilibrium. Since perceptual features have been shown to be a core determinant of similarity-based/taxonomic relationships, whereas complementary-based/thematic processing relies mainly on contextual relationships, we interpreted our findings in terms of the differential recruitment of one of the two systems of semantic relationships (taxonomic vs. thematic). Moreover, these two distinct and parallel systems have previously been reported to coexist - and compete - in healthy adults. We thus argue that controls automatically drew on similarity-based/taxonomic relationships, leading to a significant priming effect for visual features but not for contextual ones. By contrast, their impaired perceptual features forced the SD patients to resort to the system of thematic relationships

Towards a Left MTL Specialization for Arbitrary-Associative Learning? A Multiple-Case Study

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Nonspecific Effects of Normal Aging on Taxonomic and Thematic Semantic Processing

International audienceObjectiveThis study aimed to assess the effect of normal aging on the processing of taxonomic and thematic semantic relations.MethodWe used the Visual-World-Paradigm coupled with eye-movement recording. We compared performance of healthy younger and older adults on a word-to-picture matching task in which participants had to identify each target among semantically related (taxonomic or thematic) and unrelated distractors.ResultsYounger and older participants exhibited similar patterns of gaze fixations in the two semantic conditions. The effect of aging took the form of an overall reduction in sensitivity to semantic competitors, with no difference between the taxonomic and thematic conditions. Moreover, comparison of the proportions of fixations between the younger and older participants indicated that targets were identified equally quickly in both age groups. This was not the case when mouse-click reaction times were analyzed.ConclusionsFindings argue in favor of nonspecific effects of normal aging on semantic processing that similarly affect taxonomic and thematic processing. There are important clinical implications, as pathological aging has been repeatedly shown to selectively affect either taxonomic or thematic relations. Measuring eye-movements in a semantic task is also an interesting approach in the elderly, as these seem to be less impacted by aging than other motor responses

Does the left posterior fusiform gyrus play a critical role in fruit and vegetables categorization? Evidence from 19 semantic dementia patients

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La démence sémantique : un bon modèle clinique de perte du système sémantique.

International audienceIn this article, we discuss Semantic Dementia (SD) as a clinical model of semantic system loss. We provide arguments in favor of heterogeneous semantic breakdown, regarding the nature of the knowledge assessed. We rely more specifically on two recent works by our team highlighting that thematic relationships, organizing knowledge based on their complementarity within an event, have a particular status in SD. This knowledge appears to be residual, more robust to the disease, and may be over-activated in SD patients. In addition, these results support the hypothesis of a semantic disequilibrium between two types of semantic processing, namely the taxonomic and the thematic processing. This hypothesis states that the two semantic processing are kept in balance in the healthy subjects. In SD, due to the taxonomic processing disorder, thematic processing is favored. Such an internal reorganization emphasizes that the SD constitutes a good clinical model for the disorganization of semantic processing, and not a good model for the loss of the semantic system, in the sense of a unique and amodal system.Dans cet article, nous discutons de la démence sémantique (DS) en tant que modèle clinique de perte du système sémantique. Nous apportons des arguments en faveur d’atteintes sémantiques hétérogènes, selon la nature des connaissances évaluées. Nous nous appuyons plus précisément sur deux récents travaux de notre équipe soulignant que les relations thématiques, organisant les connaissances sur la base de leur complémentarité au sein d’un événement, présentent un statut particulier dans la DS. Ces connaissances apparaissent comme étant résiduelles, plus robustes à la maladie et pouvant être activées de façon exagérée chez les patients DS. En outre, ces résultats étayent l’hypothèse d’un déséquilibre sémantique entre deux types de traitements sémantiques, à savoir les traitements taxonomique et thématique. Cette hypothèse stipule que les deux traitements sémantiques sont maintenus en équilibre chez le sujet sain. Dans la DS, du fait de l’atteinte du traitement taxonomique, le traitement thématique est avantagé. Une telle réorganisation interne vient souligner que la DS constitue un bon modèle clinique de désorganisation des traitements sémantiques et non pas un bon modèle de perte du système sémantique, au sens d’un système unique

Overreliance on Thematic Knowledge in Semantic Dementia: Evidence From an Eye-Tracking Paradigm

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