May I have your attention please? The Nominal Stimulus vs. The Functional Stimulus



What’s that?

Sorry, I wasn’t paying attention.

You’ll see this happen in some case studies, research articles, classrooms, and even therapeutic practice. A situation laid out with everything in mind to elicit the predictable response. You ask “What’s two plus two?” and eagerly await the “four!”…but it doesn’t happen. You call out to someone who’s wandered off “Hey! Over here!”, and they keep on walking. You picked out your discriminative stimulus so well but the response had little or nothing to do with it. You were missing the big piece of responding to stimuli that is absolutely obvious on paper, but so easily overlooked: Attention.

Stimulus-Response contingencies are a good place to start with explaining why this is so important, because they’re often the simplest and easiest to explain. One thing happens, a response follows it. The in-between that goes unsaid is that the respondent was actually able to perceive the stimulus, otherwise the response was either coincidental or unrelated. The stimulus that is never perceived, or attended to, is called a Nominal Stimulus. It happened. It was presented purposefully. It’s not a discriminative stimulus. It plays no role in selection. The individual is unaware that it even occurred. Nominal stimuli are the “everything else” in a situation that the intended respondent is not attending to.

Imagine a teacher in a classroom helping a student write their name. They first prompt by demonstrating how the name is written. The student does not copy it. So they take the student’s hand and physically guides them through the name writing start to finish, then they reinforce with some great descriptive praise to reinforce. Great! The student learned something, right? They’re more likely to at least approximate name writing in the future, right? How about the first letter?

Not if they were looking up at the ceiling the whole time. Nominal Stimulus.

The teacher may have set up a great visual demonstration, planned out a prompting strategy, and planned out a reinforcer to aid in learning the target behavior- but not one of those things were effective, or even meets their respective intended definitions, without the student’s attention. What the teacher was actually looking for, with any of their attempts, was a Functional Stimulus.

A functional stimulus, attended by an individual, that signals reinforcement for a specific behavior? That is the feature of the discriminative stimulus (SD) that elicits previously reinforced behavior. It’s received by the respondent in a meaningful way.

The lesson here in this distinction is that observers can sometimes assume stimulus-response relations or failures in responding because they are working with situations that present Nominal Stimuli instead of Functional Stimuli. Without distinguishing the attendance of the respondent, one could simply document a discriminative stimulus occurred when it had not. That would lead to inaccurate data, and further inaccurate intervention development based on those inaccuracies.

Check for attention. Always. It may not always be the easiest thing to discern. Auditory attending is not as easy to infer as visual attending is, but by keeping the nominal and functional stimuli in mind, you are in a better place to test for conditions that better facilitate both.

Let’s try one more example.

Take this guy in the car. He’s got his phone out. Just got a text. Now THAT was one sweet discriminative stimulus. Tons of reinforcement history signaling behind that one.


The street lights in front of him? Nominal stimuli.
The stop sign down the road? Nominal stimulus.
The cars on either side of him? Nominal stimuli.

Not all unattended stimuli are nominal stimuli exactly, but in a society, these signals (lights, signs, other people’s proximity) are delivered with the intended purpose of changing or governing the responses of people in order to make sure everyone drives in an orderly and safe(ish) way. Even when a person is attending, partially, to an array of stimuli around them; all supposedly “important” in one way or another, some don’t actually register without specific attention.

One more example. Last one, I promise.


An instructor is working with a non-verbal child to build communication. They are seated at a desk. The child is staring off at one of the walls and reciting some continuous vocal stereotypy to themselves. The instructor is guiding a communication board- a page with the alphabet on it.

They… rapidly… move the board’s position in front of the child’s finger, anticipating and…prompting… the words “I W A N T L U N C H”. They stand up with glee and reinforce this…method… with a “Great job! Let’s get lunch!”. The child continues to stare off at the wall, and continue the repetitive stereotypy until lunch is brought over.

What might that instructor infer from this process if they were not thinking about nominal stimuli? Well, they might infer that the process was in any way impacted by the child’s responding. Or, that the board and prompting was received in any way by the child. It could get a little confusing.

That’s the importance of nominal and function stimuli.

Questions? Comments? Likes? Leave them all below!


Healy, A. F., & Weiner, I. B. (2013). Experimental psychology. Hoboken, NJ: Wiley.

Ormrod, Jeanne Ellis. (2012) Human learning /Boston : Pearson

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