Qualitative and aqualitative intensity components of odour mixtures

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Abstract
The perception of the intensity of components of odorous mixtures is related to the overall mixture intensity in a complex manner which has not so far been adequately modelled. Hypoadditivity, where the total perceived intensity of a mixture is less than the sum of the component intensities which arise when the substances are presented in pure form at equivalent chemical concentrations, has been known for many years. An experiment on series of 56 mixtures of amyl butyrate and bergamot at supra-threshold concentrations found that the total qualitatively unspecified intensity of such mixtures can be greater than the sum of the identified component intensities as judged in the context of the mixture. To reconcile an apparent contradiction, and to bring into one psychophysical framework results from diverse procedures, a model of mixed qualitative and aqualitative odour intensity is advanced, incorporating some evidence on the difference between detection and recognition processes. Each component in a mixture may, in this theory, both partially mask the qualitative intensity of the other, and simultaneously convert some part of the other's intensity into an aqualitative form.