The character of interhemispheric speech asymmetry in aphasia disorders and its influence on quantitative markers of speech perception and aphasia dynamics

Abstract

Introduction. In neuropsychological practice the dichotic listening task has been widely used for more than 50 years as a valid test for determining the laterality of auditory speech asymmetry. Theoretical analysis. Most of the studies of the dichotic listening task in aphasia are characterized by small sample groups, a wide demographic features of them, lack attention to the type and aphasia severity, a size of local brain damage as well. Without taking into account these important factors it is difficult to answer to some questions: 1. whether the vector of auditory speech asymmetry is determined by the age, type and aphasia severity; 2. whether the laterality of auditory speech asymmetry affects the dynamics of aphasia recovery. The aim of the study: the connection between quantitative parameters of the dichotic listening task and the dynamics of aphasia regression. Empirical analysis. Material. The study involved patients (N = 109) with traumatic and post-stroke efferent motor (50.7 ± 10.1 years) and acoustic mnestic (54.4 ± 8.2 years) aphasia of mild and moderate severity of speech disorders. Methods. Kimura’s dichotic listening task modified by B. S. Kotik; the quantitative assessment of speech in aphasia L. S. Tsvetkova, T. V. Akhutina, N. M. Pylaeva. The speech assessment was carried out twice: before and after a 6-week course of speech rehabilitation. Results. Between efferent motor and acoustic mnestic aphasia groups the difference in the laterality of ear superiority was revealed. The efferent motor aphasia group shows the ambidextrous pattern in auditory perception. The dichotic listening task efficiency increases with a burst of the left ear productivity and vice versa with the right ear. The acoustic mnestic aphasia group presents a pronounced effect of the right ear suppression. Its productivity is significantly lower than the productivity of the left ear and the same indicator of the efferent motor aphasia group. The effectiveness of the dichotic listening task in the acoustic mnestic aphasia group does not exhibit a correlation with the parameters of productivity of the right or left ear. The aphasia groups vary in the dynamics of aphasia regression. In the acoustic mnestic aphasia group, this dynamics was 2.5 times higher than in the efferent motor aphasia group. Conclusion. The right hemisphere laterality in auditory speech perception correlates positively with the dynamics of aphasia regression. Further research should find an answer to the question of the constellations of significant factors and their hierarchical relationships that could determine the positive dynamics of recovery of aphasic disorders.

Keywords

• aphasia
• speech recovery
• dichotic listening task
• right hemisphere
• interhemispheric asymmetry
• interhemispheric interaction
• ear superiority