Left-hemisphere dominance for processing of vowels: a whole-scalp neuromagnetic study

Brain activation of 11 healthy right-handed subjects was studied with magnetoencephalography to estimate individual hemispheric dominance for speech sounds. The auditory stimuli comprised binaurally presented Finnish vowels, tones, and piano notes in groups of two or four stimuli. The subjects were required to detect whether the first and the last item in a group were the same. In the left hemisphere, vowels evoked significantly stronger (37-79%) responses than notes and tones, whereas in the right hemisphere the responses to different stimuli did not differ significantly. Specifically, in the two-stimulus task, all 11 subjects showed left-hemisphere dominance in the vowel vs tone comparison. This simple paradigm may be helpful in non-invasive evaluation of language lateralization.