Which schedule reinforces after a certain number of responses that varies unpredictably?

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

Answer: (B)

Reinforcement occurs after a changing, unpredictable number of responses. This is a Variable Ratio schedule. Because the number of responses required isn’t predictable, the subject keeps responding at a high, steady rate, always uncertain about when the next reinforcement will come. Slot machines are a familiar example: rewards appear after an unpredictable number of pulls, so players continue to play eagerly.

If the requirement were fixed, like after exactly a certain number of responses, you’d see a burst of responding followed by a pause. If reinforcement depended on time rather than number of responses, a fixed interval would produce responses that creep up as the time window closes, then pause after the reward. A variable interval would reinforce after varying time gaps, yielding a steadier but slower rate of responding where timing, not the number of responses, determines reinforcement.