Motivating Operations and Discriminative Stimuli


The Simple Way to Remember MOs vs SDs

First things first, don’t think you’re alone when it comes to struggling with motivating operations and discriminative stimuli. Other than single subject design, my BCBA friends and my friends preparing to become BCBAs have an extremely difficult time wrapping their heads around motivating operations. It’s easy to discount MOs because we often leave it out when talking about behavior. Our three-term-contingency doesn’t even include it, ABC (antecedent, behavior, consequence) or SD-R-C (discriminative stimuli, response, consequence). So, what is an MO and how does it relate to an SD?

Order of Operations

The MO is considered the first part of the four-term-contingency. Yes, there is another contingency. This one is exactly the same, but with MO added. It might look something like MO-> SD -> R -> Consequence. It just isn’t used nearly enough in actual applied behavior analysis practice. But, enough background. You want to know what a MO is and how you’re going to remember it for youre exam?

What do motivating operations.. do? Motivate?

Simply: Motivating operations make you want or not want something. MOs change the value of reinforcers. I’m stranded in a dessert, I haven’t drank water for 2 days, I am very thirsty. The value of water has changed significantly because the motivation for water has changed. When we are implementing satiation or deprivation we are manipulating motivating operations. In other words, motivating operations alter the value of consequences.

What's the difference between MOs and SDs?

This is where aspiring RBTs and BCBAs get confused. There is a difference between motivating operations and discriminative stimuli. Simply: motivating operations make you want or not want something, discriminative stimuli lets you know it’s available. You are driving down the road and Jimmy Buffet’s “Margaritaville” comes on the radio. Suddenly, you are craving a margarita. The song was the MO increasing the value of a margarita. But do you have access? Is the drink available? It isn’t available until an SD tells you it’s available. You keep driving and see a Mexican restaurant with a sign that says “Open. Ice Cold Margaritas 2 for 1.” This is your SD. That sign is signaling to you that your margarita is now available.

Summing it all up.

Motivating operations make you want or not want something. MOs evoked mands, a common verbal behavior that is taught using applied behavior analysis. To learn more about verbal operants, read our blog: Verbal Behavior and Verbal Operants

Discriminative stimulis (SDs) signal these things are available.

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