Facial EMG responses to auditory stimuli.

Three studies were performed to investigate the effects of auditory stimuli (pure tones and environmental noise) of different intensities on surface EMG activity recorded over five facial muscle regions (M. frontalis lateralis, M. corrugator supercilii, M. orbicularis oculi, M. zygomaticus major, M. depressor anguli oris). The results show that with presentation of tones and noises of high intensity (> 85 dB) strong facial EMG reactions over muscles of the upper face (M. frontalis lateralis, M. corrugator supercilii, M. orbicularis oculi) were evoked. Among environmental noises of different valence but the same intensity, baby's crying evoked EMG reactions over facial muscles in the mouth region, possibly indicating that the subjects demonstrated expressions of dislike during this particular stimulation. It is also discussed whether facial EMG reactions to auditory stimulation of different intensities could be connected to changes in muscle tone of the middle ear muscles. The contraction of these muscles modulates sensitivity to auditory stimulation. Thus, facial EMG activity of the muscles of the upper face could serve as an indicator of sensitivity to external auditory stimuli. However, the evaluation of pleasant and unpleasant emotional reactions in response to auditory stimulation seems to be impossible.