Which of the following schedules of reinforcement involves receiving rewards after an unpredictable number of responses?

The variable ratio schedule of reinforcement involves providing rewards after an unpredictable number of responses. This means that the reinforcement is not delivered after a set number of actions but rather varies from one instance to another. As a result, the individual learns that they need to respond multiple times before receiving a reward, but they cannot predict exactly when that reward will come.

This unpredictability can create a high and steady rate of responding because the individual is motivated to keep trying in hopes of receiving the reinforcement. This type of schedule is often seen in gambling scenarios, where participants might not know when they will win, leading to continued play.

In contrast, fixed ratio schedules provide reinforcement after a specific number of responses, fixed interval schedules deliver reinforcement after a specified time period, and continuous reinforcement occurs when every instance of a behavior is reinforced. The key characteristic of the variable ratio schedule is its unpredictability, which strongly influences behavior and persistence.