Which type of reinforcement occurs at varying response intervals?

The correct choice is based on the understanding of reinforcement schedules within the framework of operant conditioning. Variable interval reinforcement occurs when a response is rewarded after an unpredictable amount of time has passed. This means that the reinforcement is delivered at varying time intervals, which encourages the subject to continue engaging in the behavior over time, since they remain uncertain of when the reward will be received.

For example, if a person receives a reward for checking a social media account, but the reward timing varies (sometimes they receive notifications quickly, other times it takes longer), they might frequently check their account because they are unsure when they will receive the next reinforcement. This type of schedule can lead to a steady rate of response since the individual knows that rewards will come, just not when.

In contrast, the other types of reinforcement schedules illustrated in the options provide different structures. Fixed interval reinforcement, for example, rewards the behavior after a set amount of time has passed, while fixed ratio reinforcement rewards after a specific number of responses. Variable ratio reinforcement entails providing a reward after an unpredictable number of responses, which is different from variable interval as it is based on the number of responses rather than the timing.