What defines a Variable Ratio (VR) schedule?

A Variable Ratio (VR) schedule is defined by the delivery of a reward or reinforcement after an unpredictable number of responses. This means that the exact number of responses required to receive a reward can vary widely, which creates a high level of engagement and motivation for the subject.

This schedule is particularly effective in reinforcing behaviors because it instills a sense of uncertainty, similar to gambling, where the individual continues to perform the behavior (such as pressing a lever) without knowing exactly when they will receive the reinforcement. The variability of the requirement keeps the subject engaged, leading to a stronger association between the behavior and the reinforcement over time. The unpredictability of the number of responses needed promotes persistence, as the subject may anticipate the reward after each response, thereby maintaining a higher level of performance.

In context, other options describe different reinforcement schedules: a known number of responses for a fixed ratio (A), fixed intervals regardless of behavior (B), and timing-based delivery (D). These do not encompass the variability that defines a Variable Ratio schedule, which is key to its effectiveness in creating sustained behavior.