Effects of selective adaptation on coding sugar and salt tastes in mixtures

Abstract

Little is known about coding of taste mixtures in complex dynamic stimulus environments. A protocol developed for odor stimuli was used to test whether rapid selective adaptation extracted sugar and salt component tastes from mixtures as it did component odors. Seventeen human subjects identified taste components of "salt + sugar" mixtures. In 4 sessions, 16 adapt-test stimulus pairs were presented as atomized, 150-μL "taste puffs" to the tongue tip to simulate odor sniffs. Stimuli were NaCl, sucrose, "NaCl + sucrose," and water. The sugar was 98% identified but the suppressed salt 65% identified in unadapted mixtures of 2 concentrations of NaCl, 0.1 or 0.05 M, and sucrose at 3 times those concentrations, 0.3 or 0.15 M. Rapid selective adaptation decreased identification of sugar and salt preadapted ambient components to 35%, well below the 74% self-adapted level, despite variation in stimulus concentration and adapting time (<5 or >10 s). The 96% identification of sugar and salt extra mixture components was as certain as identification of single compounds. The results revealed that salt-sugar mixture suppression, dependent on relative mixture-component concentration, was mutual. Furthermore, like odors, stronger and recent tastes are emphasized in dynamic experimental conditions replicating natural situations.

Figure 1

Matrices for (A) Experiment 1—high concentrations (100 mM NaCl and 300 mM sucrose) and (B) Experiment 2—low concentrations (50 mM NaCl and 150 mM sucrose). Entries are “total identifications” and “average % identifications” for 2 trials. Sugar ([S]), salt ([N]), or water ([0]) tastes were identified with presentation of 16 test stimuli containing NaCl (N), sucrose (S), NaCl + sucrose (NS), or water (0). Gold shading highlights numbers of veridically correct responses. (A) Ten subjects identified tastes after sampling water or an adapt stimulus for <5 s adapt time in trials 1 and 2. (B) Five subjects identified tastes after sampling water or an adapt stimulus for <5 s adapt time in trial 1; 8 subjects identified tastes after sampling water or an adapt stimulus for >10 s adapt time in trial 2.

Figure 2

Averages for (A) identification of single compounds and (B) identification of components of binary mixtures. Results are derived from matrices A and B (Figure 1) combined. (A) Test stimuli were cross-adapted, self-adapted, or mixture-adapted single compounds. Characteristic tastes of sucrose (sugar) and NaCl (salt) were readily identified when preceded by water (dotted horizontal lines) or after cross-adaptation; but the tastes were equally less salient after self-adaptation or mixture-adaptation. (B) Test stimuli were extra-, ambient-, and mixture-adapted components of binary mixtures. The sugar taste component was identified more readily than the salt taste component when the mixture followed water (dotted horizontal lines). Extra component sugar taste after NaCl and salt taste after sucrose were as salient as single components after water (A). Component sugar and salt tastes after the mixture were as salient as single components following the mixture (A). The pre-adapted ambient-component sugar and salt tastes (B), exposed to self-adaptation and mixture suppression, were much less salient than the self-adapted single compounds (A).