Unconstrained oral naming performance in right- and left-hemisphere-damaged individuals: When education overrides the lesion

Abstract

Background : The nature of the contribution of the right hemisphere to the semantic processing of words is still unclear. Moreover, studies that looked at this question using a production oral naming task offered contradictory results, partly because of differences in production criteria used for this task. Aims : The goal of this study was to investigate the contribution of the right hemisphere to lexico-semantic abilities using an unconstrained oral naming task, looking at both qualitative and qualitative dimensions of the words produced, including a time-course analysis. Methods and Procedure : A total of 30 right-hemisphere-damaged (RHD), 30 left-hemisphere-damaged (LHD) without aphasia or with only a mild aphasia, and 30 control subjects (NC) were submitted to an unconstrained oral naming task. Outcome and Results : Results showed that hemisphere-damaged subjects produced fewer words than NC and that LHD produced fewer semantic categories than NC and RHD. Time-course analysis showed that, for all groups, more words were produced at the beginning of the task. Qualitatively, RHD showed a tendency to produce a lower mean degree of prototypicality than NC. Finally, the cluster analysis identified three clusters according to the overall performance, revealing an interaction between education and the presence of a brain lesion. Conclusion : Altogether, these results indicate that the impairment of the semantic processing of words following a right-hemisphere lesion might be specifically determined by the prototypicality of words, a result that has some convergence with other results in the literature at the discourse or pragmatic levels. However, results also show the existence of an interaction between the ability to look at very mild lexico-semantic impacts of a brain lesion and the influence of degree of education on these abilities. The latter result stresses the importance of a strict control of education in any studies looking at very mild language disorders in brain-lesioned individuals.