Fig. 3.

Geometric distributions for two different partial reinforcement schedules. A geometric distribution associates with successive future trials (e.g., future tones) the discrete probability that reinforcement will occur on that trial. The entropy of a geometric distribution is log(1/p(R)), where p(R) is the probability of a reinforcer on any given trial. Note that 1/p(R) is the expected number of trials to a reinforcer, just as 1/λ is the expected interval to the next reinforcer in a variable–interval protocol. The formula for the entropy of a geometric distribution is very similar to the formula for the entropy of an exponential distribution because the geometric distribution is the discrete approximation to the exponential distribution.