A variable interval (VI) schedule is an intermittent schedule where reinforcement is given for the first response after an unpredictable amount of time. The time varies around an average, such as VI 5 minutes.
Example
A learner checks a message board for a reply that arrives at unpredictable times. Checking pays off only after some time has passed, but the learner cannot tell exactly when.
What behavior looks like
VI schedules tend to produce a moderate, steady rate of responding, with few long pauses, because the learner cannot predict when the next reinforcer becomes available.
Compare with fixed interval
On a fixed interval schedule the time is the same each time. See fixed interval for the difference.
Exam tip
Interval schedules depend on time passing plus one response. Ratio schedules depend on the number of responses.
Common mistake
Mixing it up with variable ratio. Variable interval depends on time, not number of responses.
Quick check
What does VI usually produce? A steady, moderate rate of responding.
Keep studying
Reinforcement schedules ยท RBT glossary
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