title: When the zebra loses its stripes but is still in the savannah: results from a semantic priming paradigm in semantic dementia.
abstract: Studies 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.
authors: CHU Pontchaillou, service de neurologie, CMRR, Rennes, France. Electronic address: catherine.merck@chu-rennes.fr.
authors: Catherine
authors: C
authors: Merck
authors: CHU Pontchaillou, service de neurologie, CMRR, Rennes, France.
authors: Pierre-Yves
authors: PY
authors: Jonin
authors: INSERM, Unité U1077, Caen, France; Université de Caen Basse Normandie, UMR-S1077, Caen, France; Ecole Pratique des Hautes Etudes, UMR-S1077, Caen, France; CHU de Caen, U1077, Caen, France.
authors: Mickaël
authors: M
authors: Laisney
authors: CHU Pontchaillou, service de neurologie, CMRR, Rennes, France.
authors: Hélène
authors: H
authors: Vichard
authors: CHU Pontchaillou, service de neurologie, CMRR, Rennes, France; INSERM, Unité U1077, Caen, France; Université de Caen Basse Normandie, UMR-S1077, Caen, France; Ecole Pratique des Hautes Etudes, UMR-S1077, Caen, France.
authors: Serge
authors: S
authors: Belliard
mesh_terms: D000368:Aged; D003657:Decision Making; D005260:Female; D005500:Follow-Up Studies; D057180:Frontotemporal Dementia / Q000523:psychology*; D006801:Humans; D007807:Language Tests; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D011930:Reaction Time; D060865:Repetition Priming; D012660:Semantics; D013647:Task Performance and Analysis
keywords: Contextual–functional features; Semantic dementia; Semantic priming paradigm; Taxonomic relationships; Thematic relationships; Visuoperceptual features