Altering the proportion of components in a mixed fixed-ratio schedule.

Pigeons were trained under a schedule consisting of a number of fixed-ratio 100 components followed by a single fixed-ratio 10 component. The proportion of fixed-ratio 100 to fixed-ratio 10 components was varied according to several ascending and descending series within the range of 99:1 to 1:1. When this proportion was reduced to about 20:1 and below, the pause following each fixed-ratio 100 gradually decreased in length. Primes, a burst of responses at the start of the fixed-ratio 100 component, increased in frequency, and then decreased when the proportion became extremely low. Also, when the relative frequency of fixed-ratio 10 components was very high, primes were seldom observed in the first fixed-ratio 100 component following a fixed-ratio 10 component, but were distributed evenly throughout the remaining fixed-ratio 100 components.