A phenomenological model of the perceived intensity of single odorants.

The response of a model olfactory system to a single odorant is quantified by interconnecting three separate stimulus-response relationships. Together, these relationships encompass the deposition of odorant molecules onto an olfactory organ, their movement to the dendrite of the olfactory receptor neuron, their subsequent induction of action potentials, and the processing of induced and spontaneous action potentials by the central nervous system, resulting in perception and a behavioral response. Phenomena discussed within the context of the model include the behavioral threshold, central summation of responses from a number of olfactory neurons, and the effect of organ shape on olfactory detection. The intent of the model is to provide a quantitative conceptual framework for designing and interpreting experiments relating sensory input to perception and behavior. Its utility is particularly evident for insect olfaction since it enables insect sex pheromone behavioral thresholds to be estimated from the literature when bioassays or electrophysiological studies are not possible. It also derives a physiologically meaningful method for comparing behavioral thresholds among different animals, and permits comparisons of different kinds of behavioral responses in the same species. Vertebrate olfaction is treated briefly in a discussion of the effect of sniffing on the threshold of detection.