Article Figures & Data
Figures
- 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).
- Fig. 2.
A, Individual animal (gray and white symbols) and group mean (± SE; black circles and bars) data for rats initially trained in quinine versus KCl discrimination (group 1) are plotted across training phases. Performance on all trials with a lever press is depicted averaged across all stimuli in a session. To conserve space, only the first (F) and last (L) day of each training phase are shown. During training, some rats were tested for only 1 d on a given criterion; thus, last day means represent only animals that were tested for >1 d on the relevant criterion. It is clear that all of the animals learned the discrimination. B, Animals in group 1 were tested on a variety of taste discriminations, starting with the training stimuli (quinine vs KCl) followed by denatonium versus KCl, NaCl versus KCl, quinine versus KCl, water only, quinine versus KCl, and finally quinine versus denatonium. Note that the substitution of denatonium for quinine had no effect on performance, whereas substitution of NaCl for denatonium substantially disrupted performance initially, but the animals eventually learned the discrimination. Performance was severely disrupted when only water was used, as it was when animals were tested on the quinine versus denatonium discrimination. All rats were included in all testing sessions. Because individual differences in performance were generally slight there is substantial overlap in symbols, making them difficult to discern in some cases. Chance performance equaled 0.5.
- Fig. 3.
A, Individual animal (gray and white symbols) and group mean (± SE; black circles and bars) data for rats initially trained on a quinine versus denatonium discrimination (group 2) are plotted across training phases. Performance on all trials with a lever press is depicted averaged across all stimuli in a session. Once the alternation criterion during the correction procedure was lowered, performance progressively worsened until animals responded by chance when the stimuli were presented in randomized blocks. Because individual rats were tested for varying numbers of days at criteria 8 and 6, group means for these two criteria do not necessarily represent all animals (e.g., sessions 1 and 2 of criterion 6). It is clear that all of the rats could not learn this taste discrimination. B, The animals in group 2 were then trained and tested on a quinine versus KCl discrimination. Only the final phases of training and testing are shown. It is clear that these rats were able to learn a quinine versus KCl discrimination. All rats were included in all testing sessions. Because individual differences in performance were generally slight there is substantial overlap in symbols, making them difficult to discern in some cases. Chance performance equaled 0.5.
