MEG-measurements of brain activity reveal the link between human speech production and perception

Whether human speech perception depends on a biologically based link between production and perception or whether it is best characterised as a series of acoustic, phonetic, and semantic transformations has remained an unresolved issue. We addressed this question via the use of objective brain research methods combined with advanced stimulus production methodology. We removed the contribution of the periodic glottal excitation, produced by the vocal folds in the human larynx, from vowel stimuli and found that magnetic responses generated in the auditory cortex respond to this removal. The amplitude of the main deflection of the magnetic responses, N1m, decreased even though the formant settings, intensity, and duration of the stimuli were identical. Hence, because human brain activity attenuates if vowel stimuli are “distorted“ by the removal of their naturally occurring periodic excitation we conclude that speech production and perception mechanisms in the human cortex are fundamentally interrelated.