An easy-to-hard effect after nonreinforced preexposure in a sweetness discrimination.

Experiments 1A and 1B used a taste-aversion procedure with rats to demonstrate that exposure to easily discriminated flavors along a dimension (1 % and 10 % sucrose) can facilitate learning a subsequent hard discrimination (4 % and 7 % sucrose) when one of those flavors is paired with illness. Experiment 1A compared the effects of preexposure to the easily discriminated flavors against exposure to the same stimuli used in the discrimination training or no exposure at all. Experiment 1B replicated the conditions in Experiment 1A, with 2 additional days of training and unrestricted access to the flavors on CS+/CS- trials in discrimination training. Contrary to findings with multidimensional stimuli (Scahill & Mackintosh, Journal of Experimental Psychology: Animal Behavior Processes, 30, 96-103, 2004; Suret & McLaren, The Quarterly Journal of Experimental Psychology, 56B, 30-42, 2003), we found that preexposure to the easily discriminable stimuli varying along a single dimension of sweetness facilitated subsequent discrimination training over the other conditions in each experiment. We discuss the results in terms of the ideas presented by Gibson (1969) and Mackintosh (Psychological Review, 82, 276-298, 1975) and in terms of hedonic variables not considered by theories of perceptual learning.