Abstract
A pigeon's pecking at each of two or three simultaneously available red keys was reinforced at different frequencies with a conditioned reinforcer, an orange key, on which 25 pecks resulted in a presentation of grain. Pecking was occasionally punished with a period of no reinforcement during which each key was dark. Both with two and with three keys, the relative frequency of pecking on a key was equal to the relative frequency of reinforcement obtained by pecks on that key. Also, the absolute frequency of pecking on each key was a linear function with zero intercept of the absolute frequency of reinforcement associated with that key. The slope of this function varied with the number of available keys; it was steeper with two than with three. The relative frequency of switching from any key (two successive pecks on different keys) approximated a linear function with zero intercept and slope slightly greater than 1.0 of the total relative frequency of reinforcement associated with the keys to which the bird could switch. However, the relative frequency of switching to a particular key often showed systematic irregularities. The invariance in these data is the equality between the relative frequency of pecks on one of two or three keys and the relative frequency of reinforcement associated with that key.