Effect of airway resistance on perceived odor intensity

Because of the wide range of human nasal anatomic configurations, some people sniff odorants against comparatively high resistances. To assess the relationship between sniff resistance and olfaction, ten subjects without nasal pathology or complaint were asked to estimate the perceived magnitude of the odorant, ethyl butyrate, at each of four concentrations and against each of four different resistances. In addition, the airflow profile of the subjects' sniffs was monitored during the performance of the odor task. As expected, perceived intensity increased with concentration, but more noteworthy was the finding that perceived intensity decreased with increasing resistance. Initially, this latter finding, together with the lack of interaction between concentration and resistance, suggested an olfactory analogue to conductive hearing losses. However, the sniffing data suggested that under the conditions of the experiment, the subjects attempted to maintain consistent sniffing behavior across the 16 different treatment combinations of concentration and resistance. These observations, taken together with the finding that subjects could estimate the perceived effort of sniffing, give support to the concept of a perceptual constancy model in olfaction. That is, olfactory magnitude may depend not only on the odorant itself, but also on the perceived effort associated with the sniff.