Brain asymmetry for verbal stimuli in relation to dichotic listening performance, verbal and nonverbal intellectual abilities

OBJECTIVES: A degree of lateralization of verbal functions could explain at least some performance variation in verbal tasks. The aim of the present paper was to investigate the relationship between perceptual asymmetry for verbal auditory stimuli and dichotic listening performance, verbal and nonverbal intellectual abilities. Since both verbal and nonverbal abilities tests were delivered through the visual modality, they allowed us to consider whether the relationship between functional asymmetry and task performance is dependent on a sensory modality. METHODS: Seventy-six right-handers with normal hearing were presented with a verbal dichotic listening task (six stop-consonant-vowel syllables 'ba', 'da', 'ga', 'ka', 'pa', and 'ta'). A free recall dichotic listening paradigm was employed without time limit for the answer. Subsequently, nonverbal and verbal ability tests were completed. RESULTS: A u-shaped relationship between the asymmetry for verbal stimuli and overall dichotic listening performance was found: individuals with greater hemispheric asymmetry reported more stimuli correctly. Moreover, a similar u-shaped relationship between the asymmetry for verbal stimuli and nonverbal abilities emerged: stronger asymmetry was connected with better performance. CONCLUSION: Our results might indicate that the asymmetry for verbal stimuli is connected not only with performance in the auditory verbal task but also with the general nonverbal intellectual abilities such as the ability to reason and solve novel problems independent of any previous knowledge