Final answer:
Behaviors are most resistant to extinction when reinforced intermittently, especially under a variable ratio schedule, due to unpredictable reinforcement which maintains consistent behavior as the subject keeps trying for a reward.
Step-by-step explanation:
Behaviors tend to be most resistant to extinction when the reinforcement is intermittent. This is because with intermittent, or partial reinforcement, the subject does not expect to receive the reinforcement every time they perform the wanted behavior. In contrast to continuous reinforcement, where a behavior is reinforced every time it occurs, making it faster to establish a behavior but also quicker to extinguish when reinforcement stops. For instance, in a fixed interval schedule like receiving medication at set times, extinction will occur quickly if the reinforcement is not provided at the expected time. However, in a variable ratio schedule, extinction occurs much more slowly because the reinforcement is given after an unpredictable number of responses, maintaining the behavior more consistently as the subject keeps trying in the expectation of a reward.