Which schedule describes reinforcement delivered for the first response emitted after an elapse of a fixed duration of time since the last reinforcement?

• A. Fixed Interval
• B. Fixed Ratio
• C. External Validity
• D. Extinction

Answer: (A)

The main concept is how reinforcement is scheduled in time-based contingencies. In a fixed-interval arrangement, reinforcement is delivered for the first response after a fixed amount of time has elapsed since the last reinforcement. So the key is that the reinforcement is tied to that elapsed time, not to a specific number of responses. After the interval ends, the first response gets reinforced, which often leads to a burst of responding as the end of the interval approaches and a brief pause right after reinforcement.

This differs from a fixed-ratio schedule, where reinforcement depends on a predetermined number of responses rather than time. External validity refers to whether findings generalize beyond the study, not how reinforcement is scheduled. Extinction involves the cessation of reinforcement, leading to a decrease in behavior. So a fixed-interval schedule is the correct description.