In two experiments hungry rats were given access to running wheels.
When given the novel flavour, almond, prior to novel access to
the wheels, a conditioned aversion to almond was revealed by a
subsequent two-bottle test. No such aversion was found in rats
with previous experience of wheel running, whether this prior
running occurred in the absence of any novel flavour, as in Experiment
1, or following access to saccharin, as in Experiment 2. These
results suggest that the failure of rats with prior experience
of the running wheels to develop a flavour aversion (unconditioned
stimulus, US, preexposure effect) is unlikely to be due to associative
blocking. Instead it seems that increasing exposure to a wheel
produces habituation of its nausea-inducing properties.