Reinforcement delivered after a varying number of responses is characteristic of which schedule?

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

Answer: (D)

This is about how reinforcement is tied to the number of responses rather than to time. When reinforcement is delivered after a changing number of responses, the schedule is variable-ratio. The key idea is unpredictability in how many responses are needed for a reinforcer, which makes the behavior happen at a high and steady rate with few or no breaks after rewards. This contrasts with a fixed-ratio schedule, where reinforcement comes after a set number of responses and often leads to a noticeable pause after each reward. A fixed-interval schedule reinforces after a fixed amount of time, regardless of how many responses occur, producing bursts of activity toward the end of each interval. A variable-interval schedule reinforces after varying amounts of time, yielding a steady but typically slower response rate than a variable-ratio.