Variable Interval
VI
In Plain Language
The first response after a changing period of time receives reinforcement.
ABA Definition
A schedule reinforcing the first specified response after intervals that vary around a mean.
Everyday Example
Checking messages can resemble this when new messages arrive at changing intervals.
ABA Example
A VI 2-minute schedule reinforces the first response after each varying interval, averaging two minutes.
How It May Be Used
Distinguish this response requirement from time-based, noncontingent delivery.