Probability as a determiner of rat behavior.

Abstract

In a simple choice situation, rats were able to discriminate not only a probability of unity from a zero probability to reach food (or to avoid electric shock), but also 1/2 from zero, 3/4 from 1/4 and unity from 1/2. 2/3 against 1/3 was not distinguished. Discrimination increases with the difference of the relative frequencies of success (or of punishment) on the 2 sides, as well as with their ratio. In relearning probability patterns, 3/4 to 1/4 dropped below the "threshold of probability.".