A psychophysical investigation of Beidler's mixture equation

Beidler's mixture equation (1971) describes the relationship between the concentration and composition of a binary mixture and the magnitude of the neural response. Later this equation was generalized to a psychophysical level. The purpose of the present study is to show that Beidler's mixture equation can be tested appropriately with indirect psychophysical methods, without the necessity of making assumptions about the magnitude of the maximum responses to the single compounds which constitute the mixture. Experiments were carried out using glucose and fructose as tastants. Concentrations of fructose and three equiratio mixture types containing glucose and fructose were matched in perceived sweetness intensities to five different glucose concentrations using the method of constant stimuli. The results showed that Beidler's mixture equation describes accurately the taste interaction between glucose and fructose at low sweetness levels. At high sweetness levels the taste system is more efficient, as could be expected on the basis of Beidler's mixture equation, because the experimentally determined mixture concentrations were lower than those predicted by the mixture equation. The findings suggest that glucose and fructose share common receptors, but that either one or both have additional secondary binding mechanisms.