Paradoxical adaptation to taste mixtures.

Quinine, sucrose, quinine-sucrose mixtures, and water were employed both as preadapting rinses and as stimuli in a factorial experiment. Human subjects judged the perceived taste intensity of the 16 stimulus-rinse pairs, which were flowed over the dorsal anterior tongue surface. Previously documented effects of adaptation, mixture suppression, and release from suppression were observed. Following adaptation to quinine-sucrose mixtures, presentation of equimolar unmixed quinine or equimolar unmixed sucrose resulted in a reliable residual bitter or sweet taste, respectively, which was significantly greater than the taste following self-adaptation of the unmixed solutions. The residual taste following mixture adaptation suggests a peripheral mechanism underlying suppression between bitter and sweet tastes in a mixture.