| The goal of the current study was to investigate the retrieval of phonological word forms during the speech production of persons with aphasia, in order to inform models of the structure and function of the phonological lexicon. Using a naturalistic, connected speech task (picture description) and a more structured, single-word production task (picture naming) several characteristics of the target and its phonological 'neighbourhood' were examined, specifically: the target word's frequency of occurrence; the number of words which are phonologically similar to the target (neighbourhood density); and the average frequency of those 'neighbours' (neighbourhood frequency).; To assess the influence of these factors on a target's susceptibility to error, the neighbourhood values of the words produced incorrectly in the picture description task were compared to those of a comparable corpus of correctly produced words from the same speech samples. In the naming task, target susceptibility was assessed by analyzing the error rates on individual stimulus items. The results of both tasks indicated that the lower a target's frequency of occurrence was, and the fewer neighbours it had, the more susceptible it was to error. To assess the impact of the neighbourhood on the outcome of the error, neighbourhood values of the errors produced were compared to those of their targets. In neither task were errors found to differ significantly from their targets in frequency or neighbourhood density.; These results contribute to the literature on lexical access primarily by extending findings of neighbourhood effects in normal speech production to the aphasic population. In doing so, the present study lends support to the basic tenets of the Neighborhood Activation Model (Luce & Pisoni, 1998), and to the notion of the continuity thesis, in which aphasic deficits are hypothesized to reflect quantitative, rather than qualitative, differences from normal processing. Results are also in{09} agreement with previous studies illustrating that aphasic error outcomes are strongly constrained by a number of linguistic factors which also constrain normal error production. Results are interpreted as consistent with an interactive connectionist framework of speech production. |
