Fig. 1.

Dose–response functions illustrating the lick-suppressing effects of two bitter substances [quinine hydrochloride (QUI) and denatonium benzoate (DEN)]. Behavioral-suppression scores for each stimulus concentration were derived by taking the ratio of licks during stimulus trials relative to licks during water trials (only the last 3 sec of the 5 sec trials were used to eliminate the initial sampling response). Logistic functions were fit to the group mean data. In choosing matching stimulus concentrations to be used in the discrimination experiment, three quinine concentrations representing the dynamic range of lick suppression were first identified. Isoresponse concentrations of denatonium that suppressed licking to the same degree as the array of quinine concentrations were then derived (dashed lines and arrows).