What type of reinforcement schedule rewards a response at unpredictable time intervals?

The correct choice is the variable interval schedule because it involves providing reinforcement after an unpredictable amount of time has passed since the last reinforcement. This unpredictability encourages consistent responses from individuals, as they cannot predict when the next reward will come. For instance, waiting for a bus could be considered a variable interval schedule—sometimes it arrives sooner, and sometimes it takes longer, leading to continuous checking.

In contrast, the other reinforcement schedules differ in their structure. A fixed ratio schedule provides reinforcement after a specific number of responses, leading to a predictable pattern of rewards based on the quantity of behavior performed. Continuous reinforcement offers rewards for every occurrence of the desired behavior, which can quickly establish behavior but does not maintain it as well over the long term. Lastly, a fixed interval schedule gives reinforcement after a set period, leading to a pattern of responses that tends to increase as the time for reinforcement approaches but is also predictable.