Contrast effects in flavour preference learning.

In four experiments the role of contrast effects in producing learned flavour preferences was examined. The experiments showed that contrast effects are pervasive in flavour preference learning, producing results that are often paradoxical from a traditional reinforcement point of view. In Experiment 1, rats preferred a reinforced flavour over a nonreinforced flavour more if the reinforcer was 1% sucrose than if the reinforcer was 8% sucrose. Because the cue flavour was dissolved in 8% sucrose, this represents an anticipatory positive contrast effect. In Experiment 2, the relationship between cue and consequence was shown to be important in flavour preference learning, as expected if contrast effects are involved. In Experiment 3, rats preferred a flavour that was reinforced 4 times, and they preferred this flavour more than one reinforced 8 times, presumably because the greater the expectancy of the consequence, the greater the anticipatory negative contrast. In Experiment 4, rats consumed less of 0.15% saccharin if they received 32% sucrose randomly 90 min either before or after the 0.15% saccharin than if they received only 0.15% saccharin, a simultaneous negative contrast effect.