Neuropsychological Double Dissociation between Linguistic Levels: Clinical Linguistic Evidence from Iranian Aphasic Patients

Introduction: In this paper we report on clinical linguistic applications of several versions of the Bilingual Aphasia Test (BAT) and the Persian Aphasia Battery (PAB) developed to assess patterns of recovery and language impairments in monolingual and bilingual aphasics with different clinical histories living in Iran. Methods: The participants are adult monolingual native speakers of Persian or polyglot speakers whose second or third language is one or two of the local languages, local dialects and/or English or German among the educated multilingual population. The recovery pattern and level of language impairments of each patient were assessed based on his or her clinical linguistic profile as well as analysis of the connected speech samples. Results: The linguistic profiles of monolinguals and different recovery patterns of the bilingual patients support the idea that language-specific impairments correspond to the structural properties of Persian language. The results also support incidence of selective impairments of different language skills in patients with the same lesion site. As an incidence of double dissociation the data indicated that Broca’s and Wernicke’s aphasics behaved differently. The mean syntactic comprehension scores of Broca’s patients were four times higher than that of the Wernicke’s patients (4.25 vs. 0). On the contrary Wernicke’s patients mean MLU was three times higher than that of Broca’s aphasics (6.9 vs. 2.30). Discussion: The clinical linguistic evidence from a heterogeneous group of case studies using the BAT and the PAB assessing Persian aphasics support dissociation of impairment between different levels of language, spoken and written skills. The data from patients with different lesion sites could explain the idea of under specification of functional anatomy of the classical brain-language model.