Which phrase describes a scenario where behavior is reinforced after a variable number of trials?

The phrase that describes a scenario where behavior is reinforced after a variable number of trials is a variable ratio schedule. This type of reinforcement schedule means that the reward is given after an unpredictable number of responses, which leads to high and steady rates of behavior because the subject does not know when the next reinforcement will occur. This unpredictability keeps the individual engaged, as they continue to perform the behavior in anticipation of a potential reward.

In contrast, a fixed interval schedule provides reinforcement after a specific amount of time, leading to a certain pattern of behavior, such as increased responses as the time for reinforcement approaches. Continuous reinforcement offers a reward every time the desired behavior is performed, which can lead to quick learning but may result in faster extinction once the reinforcement stops. A fixed ratio schedule requires a set number of responses for reinforcement, which can create a distinct pattern of behavior that differs from the more random nature of a variable ratio schedule.