Lateralization of Auditory Speech Asymmetry in Aphasic Disorders and the Influence of Its Vector on the Efficiency of Dichotic Listening to a Series of C-V-C Words and the Dynamics of Speech Recovery

Abstract

The dichotic listening task is commonly used in a wide range of neuropsychological issues for studying interhemispheric asymmetry and interhemispheric interaction mechanisms. The article aims to determine the specific vector of auditory speech asymmetry for efferent motor and acoustic mnestic aphasia and its correlation with the dynamics of speech recovery. The paper studied the frequency of the right and left vectors of auditory speech asymmetry in aphasics with different time post-onset and structural characteristics of lesions. Also, the paper analyses the influence of the ear advantage side on the efficiency index of dichotic listening and quantitative indicators of speech. Material. Patients with acoustic mnestic (n = 52) and efferent motor aphasia (N = 58) of moderate and mild severity. Methods. The dichotic listening task: 16 paired series of 4 monosyllabic words in each. Results. Time post-onset, as well as lesion size, does not influence directly auditory speech laterality in aphasics. The frequency of occurrence of the positive and negative signs of the coefficient of the right ear has no pronounced differences between the different lesion sizes and time post-onset in aphasia. The left hemisphere lesion marks the impairment of the reciprocity in hemispheric interaction. The left ear advantage influences positively the dichotic listening efficiency index. Aphasia recovery does not have a direct conjugacy with the side of lesion or ear advantage. At the same time, the left ear advantage in acoustic mnestic aphasia creates a more pronounced “positive shift” in speech scores than in efferent motor aphasia. Conclusion. It appears that interhemispheric speech reorganization is determined apart from topical, typological, time post-onset and the left-handedness factors by others that needed to be investigated.