Morpho-syntactic processing of regular and irregular formations in Arabic aphasia / Tariq Khwaileh

Morpho-syntactic processing of regular and irregular formations in Arabic aphasia / Tariq Khwaileh. In "Perspectives neuropsycholinguistiques sur l'aphasie - NeuroPsychoLinguistic Perspectives on Aphasia", colloque international organisé par l'Unité de Recherche Interdisciplinaire Octogone de l'Université Toulouse II-Le Mirail (France). Toulouse, 21-23 juin 2012.

Within the study of impaired morpho-syntax in aphasia, regular and irregular formations have received special attention. Dissociations in processing regulars and irregulars have been found in participants with aphasia (e.g. Miozzo, 2003). Ullman et al. (1997) have assumedthat irregular forms are retrieved as full entities while regular forms are compiled on-line. Therefore, the dissociation observed in aphasia is a result of selective impairment to one of these processes. In contrast, Joanisse and Seidenberg (1999) have assumed that regular and irregular forms are processed using a single mechanism, suggesting that the dissociation observed in aphasia may be reflecting different levels of impairment i.e. semantic vs.phonological. It is noteworthy that these two views are not flawless. While findings from previous studies have confirmed certain aspects of a given model, they were inconsistent with other assumptions of the same model.These discrepancies in both models warrant further investigation in Arabic which offers a unique opportunity to study this phenomenon due to its morpho-syntactic features. Arabic words are composed of two morphemes: a consonantal root (delivering lexical meaning) and avocalic pattern (delivering syntactic information, i.e. gender and number). This feature enables morphological dissection of semantics and syntax which is a unique method, by which data from Arabic can be analyzed. The aim of this study is to investigate morpho-syntacticprocessing of regular and irregular inflected formations of Arabic plurals through unique qualitative analysis, in which syntax is isolated from lexical semantics on a surface level. A picture-naming test (90 items) for plural formations in Arabic was developed to capture differences in the retrieval of regular and irregular plural forms. Stimuli were matched for phonological length, imageability, age of acquisition, visual complexity of stimuli, nameagreement and reaction time to naming from controls. Three participants with aphasia (RA: agrammatic production and comprehension; YA: agrammatic comprehension only; LA: agrammaticproduction only) were asked to name presented pictures with the appropriate plural form. Stimuli appeared in three conditions: dual plural (regular), sound plural (regular) and broken plural(irregular). Double dissociation in processing regulars vs. irregulars was evident at four levels: response accuracy, reaction time, error type and form. LA and YA were better at naming regular plurals than irregular ones. RA was better at naming irregular plurals than regular ones. Error type analysis revealed patterns of morpho-syntactic errors that are governed by regularity, and omissions formed the vast majority of errors in regular plurals while substitution was the only error mechanism that occurred in irregular plurals. The dissociation was statistically significant for retrieval of vocalic patterns but not lexical meaning, suggesting that the participants’ selective impairment was an effect of the regularity of morpho-syntax. These results further suggest that irregularly inflected forms are stored while regular forms are derived, which is compatible with the dual-mechanism model (Pinker and Ullman, 2002), but not with the single-mechanism model (Joanisse and Seidenberg, 1999). The current findings yield information from Arabic that contribute to the validation of findings from previous studies, and provide a new analysis technique for data from languages with non-concatenative morpho-syntax.