Which type of reinforcement schedule provides reinforcement after varying amounts of time?

The correct answer, which pertains to the type of reinforcement schedule that provides reinforcement after varying amounts of time, is the variable-interval schedule. In this schedule, reinforcement is delivered after an unpredictable amount of time has passed since the last reinforcement, which means that the timing of the reinforcer varies. Because the time interval is unpredictable, this can result in a steady and persistent response, as the subject cannot anticipate when the next reinforcement will come. This unpredictability encourages regular engagement with the behavior, as the individual learns that there is a chance of receiving reinforcement at any moment during the interval.

In contrast, other schedules like the fixed-ratio schedule deliver reinforcement after a specific number of responses, leading to a more predictable pattern of reinforcement based on behavior rather than time. The continuous schedule provides reinforcement for every occurrence of the behavior, which differs from seeking reinforcement based on fluctuating time intervals. Lastly, the fixed-interval schedule gives reinforcement after a set amount of time has passed, making it predictable rather than variable. Thus, the key feature of the variable-interval schedule—varying reinforcement timing—is what makes it unique and effective in promoting sustained behavior.