What characterizes a Variable Interval (VI) schedule?

A Variable Interval (VI) schedule is characterized by reinforcement that occurs after an unpredictable and varying amount of time has passed since the last reinforcement, provided that the desired behavior has occurred. This means that the time interval between reinforcements changes from one instance to the next, making it difficult for the individual to predict when the next reinforcement will be received.

This unpredictability encourages a steady and consistent rate of responding since the individual does not know when the next reward will come but knows that a reward will eventually follow the behavior. Therefore, the focus is on the variability in timing, rather than the frequency or number of responses that trigger the reinforcement. In this schedule, unlike fixed schedules, the timing is not regular, which often leads to a higher rate of response compared to fixed interval schedules.