Asymmetry of pleasant vs. unpleasant odor processing during affective judgment in humans

The objective of the present study was to investigate interactions between odor hedonic tone, perceived odor intensity, olfactory judgments and stimulated nostril laterality. Subjects were stimulated in the right and the left nostril separately, with two odors: vanillin (pleasant); and indole (unpleasant). They had two tasks to perform: an intensity judgment; and an affective judgment. Two concentrations (one strong and one weak) of each odor were presented. Odors were presented for a short period corresponding to one inhalation (about 1 s). The inter-stimulus interval was always 30 s. The nostril stimulated and task presentation order were counterbalanced according to a Latin square. Odor presentation order was randomized for each subject. Results indicated that response times for unpleasant odors were significantly shorter than for pleasant odors during affective judgment and right nostril stimulation, indicating greater right hemisphere efficiency for the decoding of unpleasant affects induced by odors.