Fear Odor Facilitates the Detection of Fear Expressions Over Other Negative Expressions

In a double-blind experiment, participants were exposed to facial images of anger, disgust, fear, and neutral expressions under 2 body odor conditions: fear and neutral sweat. They had to indicate the valence of the gradually emerging facial image. Two alternative hypotheses were tested, namely a "general negative evaluative state" hypothesis and a "discrete emotion" hypothesis. These hypotheses suggest 2 distinctive data patterns for muscle activation and classification speed of facial expressions. The pattern of results that would support a "discrete emotions perspective" would be expected to reveal significantly increased activity in the medial frontalis (eyebrow raiser) and corrugator supercilii (frown) muscles associated with fear, and significantly decreased reaction times (RTs) to "only" fear faces in the fear odor condition. Conversely, a pattern of results characterized by only a significantly increased corrugator supercilii activity together with decreased RTs for fear, disgust, and anger faces in the fear odor condition would support an interpretation in line with a general negative evaluative state perspective. The data support the discrete emotion account for facial affect perception primed with fear odor. This study provides a first demonstration of perception of discrete negative facial expressions using olfactory priming.