Second-order optional avoidance as a function of fixed-ratio requirements.

Two rhesus monkeys responded on a fixed-ratio schedule in Stimulus 1 (blue light) to avoid the onset of Stimulus 2 (green light). Failure to avoid Stimulus 2 required a second fixed-ratio performance to avoid Stimulus 3 (red light) in the presence of which unavoidable shock occurred. Relative frequencies of avoidance performance in the blue light and in the green light were inversely related to the ratio requirement under each stimulus condition. Both differential response-cost and avoidance-failure probability factors were related to the observed changes.