Olfactory self- and cross-adaptation: effects of time of adaptation on perceived odor intensity.

The time-course of self- and cross-adaptation of the olfactory system was investigated for two constant concentrations of three odorous substances. The substances (hydrogen sulfide, dimethyl disulfide, and pyridine) were matched, in a pilot experiment, with regard to perceived odor intensity. The time of adaptation was controlled by the number of inhalations (1-10). A two-step scaling method, involving cross-modality matching and numerical scaling of the matching continuum, was used for measuring perceived odor intensity during adaptation. The results show that the time-course function for self-adaptation seems to be an exponential function for two of the substances (H2S, DMDS), while for the third (pyridine) the form of the function is less distinct. Cross-adaptation between substances was found for the high concentrations, while for the low concentrations, hydrogen sulfide and dimethyl disulfide gave rise to pronounced cross-facilitation. The latter effect increased with time of adaptation.