Sequential Unfolding of Novelty and Pleasantness Appraisals of Odors: Evidence From Facial Electromyography and Autonomic Reactions

We investigated the effects of odors on appraisal processes and consequent emotional responses. The main goal was to test whether an odor is detected as novel or familiar before it is evaluated as pleasant or unpleasant. Participants performed a recognition task in which they were presented with pairs of unpleasant or pleasant odors (sample and target odors). Within a pair, the sample and target were either identical or different to assess participants' novelty detection; unpleasant and pleasant target odors were contrasted to examine participants' appraisal of intrinsic pleasantness. We measured facial expressions using electromyography and physiological reactions using electrocardiogram and electrodermal activity in response to odors. The earliest effects on facial muscles and heart rate occurred in response to novelty detection. Later effects on facial muscles and heart rate were related to pleasantness evaluation. This study is the first to demonstrate the existence of a sequence of appraisal checks for odors eliciting emotional reaction.