Basic emotions evoked by odorants: comparison between autonomic responses and self-evaluation

The present study was designed to analyze the relationship between self-report and physiological expression of basic emotions (happiness, surprise, fear, sadness, disgust and anger) in response to odorants. 44 subjects inhaled five odorants: vanillin, menthol, eugenol, methyl methacrylate, and propionic acid. Six autonomic nervous systems (ANS) parameters were simultaneously recorded in real time and without interference: Skin Potential (SP), Skin Resistance (SR), Skin Temperature (ST), Skin Blood Flow (SBF), Instantaneous Respiratory Frequency (IRF) and Instantaneous Heart Rate (IHR). At the end of the recording, subjects were instructed i) to identify the odorants roughly II) to situate them on an 11-point hedonic scale from highly pleasant (0) to highly unpleasant (10); and iii) to define what type of basic emotion was evoked by each odorant. In this study, the expected affects were aroused in the subjects. Vanillin and menthol were rated pleasant, while methyl methacrylate and propionic acid were judged unpleasant. Eugenol was median in hedonic estimation. ANS evaluation (each autonomic pattern induced by an odorant was transcripted into a basic emotion) shows that pleasantly connoted odorants evoked mainly happiness and surprise, but that unpleasant ones induced mainly disgust and anger. Eugenol was associated with positive and negative affects. Comparison between conscious (verbal) and unconscious (ANS) emotions, reveals that these two estimations 1) were not significantly different as far as the two pleasant odorants were concerned, 2) showed a tendency to be significantly different for eugenol odorant which was variably scored on the hedonic axis, and 3) exhibited a significant difference for the two unpleasant odorants, for which the corresponding "verbal emotion" was mainly "disgust", while the most frequent ANS emotion was "anger". In conclusion, these results show quite a good correlation between verbal and ANS estimated basic emotions. The main difference concerns anger: while there is a high occurrence of this emotion revealed by the analysis of ANS responses, it does not appear to be easily expressed through the verbal channel.