Testing a perceptual constancy model for odor strength: the effects of sniff pressure and resistance to sniffing.

The rate at which odorous vapor flows over the receptor surface is reflected in olfactory nerve activity, but the evidence for a corresponding effect on odor strength is scant and inconsistent. A perceptual constancy model for odor strength resolves this apparent contradiction: The effect of flow rate at the receptor site may be perceptually discounted when there is sensory feedback, in the form of perceived effort, from the action of sniffing responsible for changes in flow rate. Previous evidence shows that observers experience change in perceived effort when sniffing at various pressures against fixed resistance but not when sniffing with fixed pressure against varying resistance. Thus the model predicts both that odor strength varies when flow rate is manipulated by changes in olfactory resistance and that odor strength is invariant when flow rate is manipulated by changes in sniff pressure. In the present study, in which subjects made magnitude estimates of the odor strength of pyridine and n-butanol, an earlier finding for the effects of resistance change was confirmed and extended. Further, within the framework of a single experiment in which both pressure and resistance were independently manipulated, the odor strength of n-butanol conformed to the predictions of the constancy model.