What is a variable interval reward schedule?

• A. Reinforcement after a fixed time interval.
• B. Reinforcement after a specific number of responses.
• C. Reinforcement at a random time so that it cannot predict when the reward will occur. Goal should be two minutes.
• D. Reinforcement after a random number of responses.

Answer: (C)

A variable interval schedule reinforces the subject after an unpredictable amount of time has passed, with the length of each interval changing from reward to reward. Because the timing is not fixed, the dog cannot predict exactly when the next reward will appear, which encourages steady, consistent responding rather than pauses or bursts around a known cue. In the example, reinforcement happens at random times around a two-minute average, capturing that unpredictable timing aspect of variable interval schedules. This differs from a fixed interval (reinforcement after a set time) and from schedules based on the number of responses (fixed or variable ratio), where the reward depends on how many responses have occurred rather than when time passes.