In the present study, we investigated taste-taste, taste-vehicle, and simultaneous taste-vehicle-taste mixtures. Subjects made estimates of the sweetness and bitterness of 27 stimuli. Sucrose (292, 585, and 1170 mM, caffeine (13, 26, and 52 mM), and binary mixtures of low (292-13 mM), middle (585-26) and high (1170-52 mM) Ievels of both components were dispersed in water, carboxymethylcellulose (CMC) 1% w/v, and gelatin 6% w/v. The sweetness and bitterness of the sucrose-vehicle-caffeine combinations were significantly weaker than the respective sucrose-vehicle and caffeine-vehicle combinations. The emerged mutual suppressive effects were asymmetrical and persisted when both tastants were presented in CMC and gelatin. Moreover, the increase in vehicle consistency and the simultaneous addition of another taste reduced the perceived intensity of a taste either presented alone or dissolved in water. For both sweetness and bitterness, the total taste suppression observed was always significant.

Two experiments are reported in which the perceptual interactions between oral pungency, evoked by CO₂, and the taste of each of four tastants—sucrose (sweet), quinine sulfate (bitter), sodium chloride (salty), and tartaric acid (sour)—were explored. In experiment 1 the effect of three concentrations of each tastant on the stimulus-response function for perceived oral pungency, in terms of both rate of change (slope) and relative position along the perceived pungency axis, was determined. In experiment 2 the effect of three concentrations of CO₂ on the stimulus-response function for the perceived taste intensity of each tastant was examined. Results show that the characteristics of the mutual effects of tastant and pungent stimulus depend on the particular tastant employed. Sucrose sweetness and CO₂ oral pungency have no mutual effect; sodium chloride saltiness or tartaric acid sourness and CO₂ oral pungency show mutual enhancement; and quinine sulfate bitterness abates CO₂ oral pungency, whereas CO₂ has a double and opposite effect on quinine sulfate bitterness—at low concentrations of bitter tastant CO₂ enhances bitterness, and at high concentrations of bitter tastant CO₂ abates bitterness. It is suggested that the perceptual attributes of saltiness and sourness are closer, from a qualitative point of view, to oral pungency than are the attributes of bitterness and sweetness.

The present investigation explores the stimulus-response (psychophysical) functions for total nasal perceived intensity for two pungent odorants, formaldehyde and ammonia, presented either alone or with different backgrounds of the other irritant. Stimuli were comprised of four formaldehyde concentrations (1.0, 3.5, 6.9 and 16.7 p.p.m.); four ammonia concentrations (210, 776, 1172 and 1716 p.p.m.); and their 16 binary mixtures. Ammonia functions showed a consistent upward concavity. At low, medium and high concentrations, the total perceived intensity of the mixtures showed hypoadditivity, simple additivity and hyperadditivity, respectively. That is, the intensity of the corresponding mixtures was significantly lower than, equal to, or greater than the sum of its components. The progressive involvement of pungency, aroused by common chemical sense stimulation, may be responsible for the increasing additivity observed. Simple additivity, and even hyperadditivity, may characterize mixtures involving common chemical stimulation.