62 Herrnstein proposed that the proportion of behavior to an alternative was a function of the proportion of reinforcers available for that alternative. That perspective is illustrated in the bottom portion of the slide. The obtained function represents the behavioral equilibrium between the two schedules. This surface portrays the change in behavior as a function of both time in the fixed-interreinforcement interval and with increasing experience. With growing experience, the final and initial portion of the IRI has an increasing effect.
Avoidance first begins in the initial portion of the interval.
In conclusion, fixed intervals exert bipolar control.