A systematic review: Idiom comprehension in aphasia: The effects of stimuli and task type

Abstract

Idioms differ from other forms of figurative language because of their semantic dimensions of familiarity (frequency of encounter), ambiguity (possibility to have a literal interpretation), decomposability (possibility of the idiom's words to assist in its figurative interpretation) and transparency (possibility to deduce the original metaphorical motivation of an idiomatic phrase from its literal analysis). A variety of approaches have been used to investigate the way idioms are processed in the brain. Studying clinical populations is one of them. Supporting evidence has been drawn from studies examining subjects suffering from aphasia, typically caused by lesions to a complex language network involving the main language areas in the Left Hemisphere (LH) of the brain. Patients with aphasia sometimes show selective impairment in idiom comprehension, implying that there are types of idioms, less impaired in comprehension, which do not depend solely on the LH of the brain. However, recent literature does not seem to agree in terms of when such preference exists and if the types of idioms and tasks employed play a crucial role. This study investigates idiom comprehension in aphasia and seeks to explore (1) the effect of idiomatic stimuli in terms of their semantic dimensions on the patients' language performance (2) a potential effect of the tasks employed on the patients' language performance. A systematic review was done following the PRISMA approach. Starting from an initial find of n = 457, after applying inclusion and exclusion criteria, 15 articles were retained for further analysis. Relevant information that was extracted included differences and similarities across studies, especially focusing on patient characteristics (age, type of aphasia, severity of aphasia, post onset period, handedness, type of lesion (i.e., single focal vs. multiple), lesion location, etiology and test used for diagnosis), stimuli (types of stimuli, stimuli's assessment, consistent use of terminology) and task employed (type of task, task options, modality of presentation and response, and types of measurements) and language comprehension patterns. Results indicated that studies in idiom comprehension in aphasia are characterized by great heterogeneity regarding the experimental task and the type of idiomatic stimuli employed. Heterogeneity in these key aspects, results in unclear interpretation of idiom comprehension patterns in aphasia across studies. In addition, the nature of idiomatic stimuli and more specifically their semantic dimensions were insufficiently described, and their descriptions were sometimes accompanied by terminological inconsistencies. Moreover, patient profiles were occasionally incomplete and more importantly, language comprehension patterns were reported after considering patients with aphasia as one homogenous group irrespective of their aphasic syndrome. Last, this review proposes recommendations for future research, focusing on patient profiles, experimental tasks and stimuli as well as the interpretation of language comprehension patterns.