Herrnstein, R. J. (1961).
Relative and absolute strength of response as a function of frequency of reinforcement.
Journal of the Experimental Analysis of Behavior,
4, 267-272.
The frequency of responding on two keys is investigated as a
function of reinforcement conditions. The mean interval of
reinforcement on each key was varied from 1.5 to 9 minutes, but
the total reinforcement frequency was held constant. The relative
frequency of responding on a given key closely approximated the
relative frequency of reinforcement on that key.