Reinforcement: Variable Interval

Variable Interval: It’ll be there EVENTUALLY


Now that we’ve gone over most of the different kinds of schedules of reinforcement, it’s time for the last, but not least of the schedules: Variable Interval. 

From the name alone, we can make sense of what Variable Interval will be doing. “Variable” means randomized, while “interval” means after a set time period. Together, this means that the schedule will reinforce subjects after a randomized period of time. 

In practice, this means the subject will have to wait a randomized period of time before the window of opportunity opens for them to receive their reinforcer. If the subject is able to perform the wanted behavior during that time, then they will receive their reinforcer. 

In scientific notation, you will find notations like “VI-10” which means, on average, after 10 minutes, the subject will receive a reinforcer. This will mean the subject could receive their reinforcer after 1 minute, or after 30 minutes, but it must average out to 10 minutes. 

Everyday Examples


This schedule is what prompts us to keep checking for emails. We don’t know when emails come, but we know they come at random times during the day (unlike postal mail where there is usually a “general” time that they will appear at your house). As a result, we check our emails fairly often to make sure we don’t miss any and are rewarded at random intervals when we do check.

One can even argue that Variable Interval is also what makes social media so rewarding. We don’t know when a new and interesting post will be made, so we check social media fairly frequently to see what friends are posting or what other pages are posting to see if it’s interesting. If it is, then it’s rewarding our behavior of checking the social media app. If it isn’t then we just check again later.  

Features of Variable Interval

Much like its cousin, Variable Ratio, Variable Interval schedules create a behavior that is fairly resistant to extinction. Due to the inconsistent times a subject receives its reinforcer, you’re going to find more times where the subject is willing to not get a reinforcer and still do the behavior. 

Behavior that was taught through Variable Interval are going to show moderate, but consistent response rates (it’ll be less than Variable ratio, but more than the Fixed schedules). This is going to be best used for behaviors that your subject doesn’t mind doing a few times a day. Simple checks or reoccurring behaviors you want your subject to repeat a few times are ideal for Variable Interval. 

Let’s look at the graph to see how it compares with the other schedules of reinforcement.
All Schedules of Reinforcement Graph

You can see it’s response rates are similar to Variable Ratio, in that both create consistent rates with few breaks. It’s still higher than fixed, which can be a useful trait to keep in mind when you’re using this schedule.


Other Examples


For pets, you can see this best when they sometimes wander in to check up on you. If you give them a positive reaction during this time, then you’re reinforcing them periodically checking in on you. It’s variable since they don’t know exactly when you’re going to reinforce them, but they know after a certain amount of time you may either be done with work or in need of a break. Eventually, that window will open and they will be there for you and in turn, receive reinforcement from you. 

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