Which schedule delivers a reinforcer after the first response following a fixed amount of time since the last reinforcement?

• A. Fixed Interval (FI) Reinforcement
• B. Variable Interval (VI) Reinforcement
• C. Fixed Ratio (FR) Reinforcement
• D. Variable Ratio (VR) Reinforcement

Answer: (A)

In a fixed interval schedule, reinforcement becomes available after a specific amount of time has elapsed since the last reinforcement, and the first response after that fixed time earns the reward. The clock starts after each reinforcement, so the learner learns to respond as the end of the interval approaches, often producing a “scalloped” pattern of increasing responding toward the interval’s end. This emphasis on time guiding when reinforcement can occur distinguishes it from other schedules.

Contrast briefly with how the others work: a variable interval uses different time lengths between opportunities, a fixed ratio reinforces after a set number of responses, and a variable ratio reinforces after a varying number of responses. The description given—reinforcement for the first response after a fixed amount of time—fits the fixed interval schedule.