A fixed interval (FI) schedule is an intermittent schedule where reinforcement is given for the first response after a set, unchanging amount of time has passed, such as FI 2 minutes.
Example
A learner knows a snack is delivered at the same time each day, and checks for it only near that time. Responding usually increases as the set time approaches.
What behavior looks like
FI schedules often produce a pause after reinforcement, followed by faster responding as the interval ends. On a graph this looks like a scallop pattern.
Compare with variable interval
A variable interval schedule changes the time each round, which produces steadier responding.
Exam tip
Fixed means the amount is always the same. The reinforcer still needs one response after the time has passed.
Common mistake
Thinking reinforcement arrives after a set number of responses. Fixed interval is about time passing.
Quick check
What is reinforced on an FI schedule? The first response after a set amount of time.
Keep studying
Reinforcement schedules ยท RBT glossary
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