Influence of affective and cognitive judgments on autonomic parameters during inhalation of pleasant and unpleasant odors in humans.

Hedonic tone is so salient in odor perception that several authors have used odors to induce affective states. Various studies have shown that the electrophysiological and psychophysiological response patterns induced by olfactory stimuli are different for pleasant and unpleasant odors, and that these types of odor activate brain structures differentially. These results suggest that odors are first categorized according to pleasantness. The objective of the present work was to study the possible existence of an involuntary affective categorization in olfaction. Given that certain variations in the autonomic system, such as skin conductance amplitude and heart rate, are not under the voluntary control of human subjects, we used such psychophysiological methods for this investigation. Our results indicate that unpleasant odors provoke heart-rate acceleration during both a smelling task (control condition: a task in which subjects had only to inhale odors) and a pleasantness judgment, but not during a familiarity judgment. These results suggest that subjects involuntarily categorize odors by their pleasantness.