Reinforcement: Fixed Interval

Fixed Interval: Wait for it!

Now that we’ve covered Fixed Ratio, it’s time we cover its cousin, Fixed Interval!

Going over again from our previous article on Schedules of Reinforcement, the word “Fixed” in this scenario means that the behavior is rewarded after a set amount of whatever the trainer pleases (compared to “variable” where it’s not a set amount). “Interval” just means time is the “amount of whatever the trainer pleases.” So all together, “Fixed Interval” just means “the behavior is rewarded after a fixed amount of time.”

When you’re using this schedule of reinforcement, the subject will be reinforced after a set amount of time has passed. The best way to think of Fixed Interval (and Variable Interval for that matter) is that you’ll reinforce your subject when a specific window of time opens. For Fixed Interval, that window of time can open up every 5 minutes and as long as your subject responds in those 5 minutes, then it will receive a reinforcer.

Let’s dive into some examples.



Common uses of Fixed Interval can be seen when people are waiting for a web page to refresh with new information, or expecting some mail at a general time.

The person in question will steadily increase their behavior as the time approaches. In the web viewer’s point of view, they will start pushing the refresh button at a higher rate as the time approaches.

For our person waiting for a package, they will start checking their windows and doors more frantically until the mail arrives.

My personal favorite example of Fixed Interval Schedules happens all the time on college campuses all around the world. As deadlines for projects or tests approach, you’ll see more and more students cramming in order to finish/learn everything on time. Once the test or project has passed, the students receive their reinforcement (good grades, feeling of being done with another hurdle in their career, etc.) and then take a long break before cramming for their next test.

Features of Fixed Interval Schedules

FIxed interval schedules will create a steady rate of responses that will increase as the time window approaches. This is usually abbreviated in (FI-#), where # means the amount of time between reinforcers. For example, if a pigeon in Skinner’s box was on an FI-5, that means the pigeon will receive a reinforcer for the first peck it performs every 5 seconds.

However, just like with Fixed Ratio, the subject will pause or take a break after the reinforcer is given. Unlike Fixed Ratio, the subject will usually perform the largest number of responses just before the time window opens. Also unlike Fixed Ratio, the subject under Fixed Interval will not have a response rate as high as Fixed Ratio’s schedule. 

If we look at the chart again…


All Schedules of Reinforcement Graph

… you can see that Fixed Interval (FI) creates an almost scallop shaped response rate that is much lower than the others. This is because the subject’s response rate is spiking just before the window of time opens, and once the reinforcer is delivered, the subject is resting for longer because it has an idea of when the window of time opens again.

Other Examples


Besides the examples I’ve already listed, you’ll find these schedules used on people all the time in modern mobile games. If you’ve ever had to interact with a stamina bar or a resource on a “cooldown,” then you’re interacting with this schedule of reinforcement.

As a player, you know that your stamina will regenerate at a certain time, but that won’t stop you from just checking your game here and there across your day until you finally have enough stamina to play the next part of your game.

Gaming companies use this in order to control how much players get to interact with their games and then reinforce them for opening their app. Even a here-and-there check is being rewarded by this schedule because you are actively opening the app to see when you will receive the stamina to play the game (your reinforcer). Once you receive it and your stamina is empty, then you get to take a break until your stamina regenerates again.

This about sums up the major points of Fixed Interval Schedules. If you can think of more examples in your everyday life that’s maintained through a Fixed Interval Schedule of Reinforcement, then let me know in the comments down below!

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