MODELING THE HUMAN OLFACTORY STIMULUS-RESPONSE FUNCTION

Two models, derived from the equations of Michaelis-Menten and Hill, w ere adapted to olfaction. Their ability to model human olfactory stimu lus-response relationships was compared with that of the classical law s of Fechner and Stevens. First, these four models were systematically compared on data available in the literature concerning 20 pure odoro us compounds. At the lower concentrations of the odorous compound, the model of Stevens was found to be as good as the model of Hill. Howeve r, when the concentration range was extended further and included the concentration at half the maximum intensity, the model of Hill was fou nd to be better. Second, the four models were tested on different part s of a true stimulus-response sigmoid curve with 5% noise added. The c omparison confirmed the results obtained when experimental data were u sed. Third, the hypothesis that the psychophysical response is the sum of sigmoidal responses generated at the more peripheral parts of the olfactory system was examined, assuming a binomial distribution of rec eptor affinities. Within a very large range of variation in their char acteristics, the sums of several sigmoids are indeed correctly modelle d by Hill equations with exponents reflecting the distribution of rece ptor affinities.