In which schedule is reinforcement delivered for the first response after a set amount of time?

The correct answer is fixed interval, as this schedule provides reinforcement following the first response that occurs after a predetermined amount of time has elapsed. In a fixed interval schedule, the timing of reinforcement is consistent, which means that the individual can predict when they will receive reinforcement if they respond after the interval has passed. This leads to a characteristic pattern of responding where individuals may show low rates of response immediately after reinforcement but increase their responses as the time for the next reinforcement approaches.

In contrast, variable interval reinforcement provides reinforcement for the first response after varying amounts of time, making the timing less predictable. Continuous schedules offer reinforcement for every single response, ensuring that each behavior is followed by a reward, which is quite different from the time-based criteria of the fixed interval. Lastly, fixed ratio schedules deliver reinforcement after a set number of responses, not after time has passed, so they focus on the quantity of responses rather than the timing. Therefore, the distinct nature of the fixed interval schedule makes it the correct answer here.