Facial EMG responses to odors in solitude and with an audience.
Two experiments were undertaken to examine whether facial responses to odors correlate with the hedonic odor evaluation. Experiment 1 examined whether subjects (n = 20) spontaneously generated facial movements associated with odor evaluation when they are tested in private. To measure facial responses, EMG was recorded over six muscle regions (M. corrugator supercilii, M. procerus, M. nasalis, M. levator, M. orbicularis oculi and M. zygomaticus major) using surface electrodes. In experiment 2 the experimental group (n = 10) smelled the odors while they were visually inspected by the experimenter sitting in front of the test subjects. The control group (n = 10) performed the same experimental condition as those subjects participating in experiment 1. Facial EMG over four mimetic muscle regions (M. nasalis, M. levator, M. zygomaticus major, M. orbicularis oculi) was measured while subjects smelled different odors. The main findings of this study may be summarized as follows: (i) there was no correlation between valence rating and facial EMG responses; (ii) pleasant odors did not evoke smiles when subjects smelled the odors in private; (iii) in solitude, highly concentrated malodors evoked facial EMG reactions of those mimetic muscles which are mainly involved in generating a facial display of disgust; (iv) those subjects confronted with an audience showed stronger facial reactions over the periocular and cheek region (indicative of a smile) during the smelling of pleasant odors than those who smelled these odors in private; (v) those subjects confronted with an audience showed stronger facial reactions over the M. nasalis region (indicative of a display of disgust) during the smelling of malodors than those who smelled the malodors in private. These results were taken as evidence for a more social communicative function of facial displays and strongly mitigates the reflexive-hedonic interpretation of facial displays to odors as supposed by Steiner.