Effects of cognitive factors on perceived odor intensity in adaptation/habituation processes: from 2 different odor presentation methods.

The purpose of this study, which comprised 2 experiments, was to investigate cognitive effects on odor perception. An odor was presented using an olfactometer. In Experiment 1 ("continuous" presentation), anethole, an odor unfamiliar to most Japanese individuals, was presented continuously for 1 session (20 min), whereas in Experiment 2 ("intermittent" presentation), odor stimuli were presented 60 times for a short duration (0.2 s) over 4 sessions (24 min, including 9 min of intersession intervals), in which odor duration, temperature, and humidity were strictly controlled and the odor in the nostril was removed immediately after presentation. In each session, participants were asked to continuously evaluate odor intensity. In both Experiments 1 and 2, the participants were informed that the odor was either healthy (healthy-description group) or hazardous (hazardous-description group) prior to the session. The results show that in Experiment 2 (intermittent presentation), the hazardous-description group perceived the odor as more intense than did the healthy-description group, especially during the last 2 sessions. In Experiment 1 (continuous presentation), however, no significant difference in perceived intensity was present between the 2 groups. This study demonstrates the effect of cognitive state on perceived intensity by developing an experimental setting wherein the peripheral adaptation process was reduced and central olfactory processes were emphasized.