Detection of Heteroquality Taste Mixtures

Detection thresholds were measured for sweet (sucrose), salty (sodium chloride), sour (citric acid), and bitter (quinine hydrochloride) and for the 11 possible mixtures of these four substances. These 11 mixtures (6 binary, 4 ternary and 1 quaternary) all turned out to be stimulus additive, in the sense that a person could reliably detect mixtures whose individual components are weaker than their unmixed thresholds. Tastants too weak to be perceived alone can thus make impact when in mixtures. The threshold concentration for a given compound was reduced in approximate proportion to the number of compounds added to it. This liberal heteroquality additivity contests the widespread belief that heteroquality mixtures (different chemicals evoking different qualities) are nonadditive and homoquality mixtures (different chemicals evoking the same quality) are additive. Heteroquality additivity emerges on appropriate definition of the subject's task by forced choice (unavailable to earlier investigators), in order to skirt methodological pitfalls. Operating together, homo- and heteroquality additivity may concomitantly enable a person to sense natural mixtures of hosts of weak constituents, such as drinking water. In this regard, gustatory mixtures may function much as do mixtures of frequencies in audition and mixtures of gaseous compounds in olfaction.