Smells are no surer: rapid improvement in olfactory discrimination is not due to the acquisition of a learning set.

The claim that rats can demonstrate the 'primate-like' learning capacity of learning set formation when trained with olfactory cues, rather than visual or auditory cues, has generated considerable interest in recent years. In this study, the claim is evaluated in detail by using a series of experimental and control procedures to determine whether rats do indeed develop the abstract 'win-stay, lose-shift' strategy which underlies learning set formation in monkeys. We report here that although exposure to a series of novel olfactory discrimination problems gives rise to progressive improvement in the rate of learning, it is not a necessary condition for the development of that rapid learning. Furthermore, even rats which fail to display progressive improvement in olfactory reversal learning show rapid learning on novel olfactory discrimination problems. Each of these findings suggests that although olfactory learning may be rapid, learning set formation does not occur over a short series of problems.