Variable interval
A schedule of reinforcement in which the first response after an unpredictable amount of time is reinforced, with intervals varying around an average such as 2 minutes (VI 2-min).
On a variable-interval (VI) schedule, the length of time that must pass before a response can be reinforced changes from one interval to the next. On a VI 4-minute schedule the intervals might be 1, 6, 3 and 6 minutes, averaging 4. Once each interval ends, the first response is reinforced. As with all interval schedules, the response must still occur; the passage of time only makes reinforcement available.
Because the learner cannot predict when reinforcement will next be available, VI schedules tend to produce a steady, moderate rate of responding with few pauses. Behavior maintained on a VI schedule is also relatively resistant to extinction. Checking social media, where new messages arrive at unpredictable times, is an everyday example of behavior on a variable-interval-like schedule.
An RBT running a VI schedule usually follows a list of preset intervals or a timer app that the supervisor has set up. The RBT reinforces the first target response after each interval and records it. Picking intervals on the spot, or giving the reinforcer when the interval ends without the behavior, changes the procedure.
Example and non-example
| Example | A teen's plan calls for VI 5-min praise for on-task work. The RBT's timer vibrates after 3 minutes, then 7, then 5. Each time it vibrates, the RBT praises the next on-task behavior they see. |
|---|---|
| Non-example | The RBT praises the teen after every third completed worksheet problem, then after every fifth, then after every fourth. That is a variable-ratio schedule because it depends on the number of responses. |
Don't confuse it with
| Variable ratio | Variable ratio reinforces after an unpredictable number of responses; variable interval reinforces the first response after an unpredictable amount of time. |
|---|---|
| Fixed interval | Fixed interval uses the same interval every time and tends to produce a scallop; variable interval changes the interval and produces steadier responding. |
Test yourself
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Question 1The plan states: "Praise the first hand raise that occurs after an unpredictable amount of time has passed, averaging 3 minutes. Hand raises before that time are not praised." Which schedule is this?
Show answer
A: Variable interval 3 minutes. Reinforcement goes to the first response after an amount of time that changes around an average of 3 minutes. That is a variable interval (VI 3-minute) schedule.
- B: A variable ratio schedule depends on the number of responses, not on time passing.
- C: A fixed interval schedule uses the same interval every time, not an unpredictable one.
- D: A variable-time schedule delivers reinforcement after varying times even if the client does not raise a hand.
Task C.1 · 40-hour curriculum section A
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On the RBT exam
This term belongs to task C.1 Positive and negative reinforcement in content area C, Behavior Acquisition, which is 19 of the 75 scored questions.