What characterizes a variable-interval schedule in operant conditioning?

A variable-interval schedule is characterized by the reinforcement being delivered after varying amounts of time have passed. This means that the time between reinforcements is inconsistent and unpredictable, which leads to a steady rate of responding as the subject learns that reinforcement could occur at any time.

In practical terms, this could be likened to waiting for a bus that arrives at irregular intervals; sometimes you might wait a short time, other times longer, but you know it will arrive eventually. This unpredictability encourages a continual engagement with the behavior being reinforced because the individuals cannot predict when they will receive a reward.

In contrast, a fixed-interval schedule would provide reinforcement after a set period, leading to a pause in behavior right after the reward is obtained until the next interval starts again. Similarly, other options involving specific amounts of behavior or consistent intervals do not convey the essence of variability inherent in a variable-interval schedule, making that option distinctive and accurately describing the operant conditioning framework.