Intermittent reinforcement is used to maintain acquired behaviors. There are several schedules for reinforcement, and they all have a different affect on the behavior.
Fixed Ratio (FR) Reinforcement reinforces the behavior after every X number of times. There is a high response rate here, but the responses become irregular as involved individuals begin to recognize the pattern as to when the reinforcement will come, and that is when they display the appropriate behavior.
Fixed Interval (FI) Reinforcement occurs after X amount of minutes. This works really well just prior to the reinforcement, but it stops working after the reinforcement because the individuals know that no reinforcement will be forthcoming.
Variable Ratio (VR) Reinforcement occurs after X number of responses on an average. This has a high level of response. The greater the ratio the greater the response.
Variable Interval (VI) Reinforcement is given for the first occurrence after every X minutes. This has a more consistent rate of responding.
Both VR and VI are more resistant to extinction as their pattern is more difficult to predict.