Which reinforcement schedule requires a variable amount of time to pass before reinforcement is given, making outcomes time-based but unpredictable?

• A. Fixed-Interval Schedule
• B. Variable-Interval Schedule
• C. Fixed-Ratio Schedule
• D. Variable-Ratio Schedule

Answer: (B)

This item tests understanding of reinforcement schedules that depend on the passage of time but are unpredictable. In a variable-interval schedule, reinforcement is delivered after varying lengths of time have passed, and those intervals change around an average. Because the exact timing is unpredictable, the subject tends to respond at a steady, moderate rate rather than clustering responses right before a known payoff.

This differs from a fixed-interval schedule, where reinforcement comes after a predictable, set amount of time, often producing a burst of responding as the interval ends. A fixed-ratio schedule reinforces after a set number of responses, so timing isn’t the main factor. A variable-ratio schedule reinforces after an unpredictable number of responses, making the timing irrelevant to when reinforcement occurs and typically yielding high, steady responding.

So, the schedule that is time-based yet unpredictable is the variable-interval schedule.