Motivating operations vs discriminative stimuli

Both MOs and SDs come before behavior, and both can make a behavior more likely. That's why they're so easy to mix up. The BACB's 6th edition outline has a task for identifying examples of motivating operations (B.16) and a separate task for distinguishing motivating operations from stimulus control (B.17).

The short version:

• A motivating operation (MO) changes how much a consequence is worth right now.
• A discriminative stimulus (SD) signals that a particular response has been reinforced in this situation before.

Motivating operations: changing the value

Laraway, Snycerski, Michael and Poling (2003) proposed "motivating operation" as the umbrella term. As later summarised by Poling, Lotfizadeh and Edwards (2020), MOs have two effects:

• a value-altering effect: they change how effective a reinforcer or punisher is, and
• a behavior-altering effect: they change how often the behavior that has produced that consequence occurs.

MOs work in both directions:

• An establishing operation (EO) makes a consequence more effective. For example, going without water makes water more reinforcing, and behavior that has produced water increases.
• An abolishing operation (AO) makes a consequence less effective. For example, after a large meal, food is less reinforcing, and asking for snacks decreases.

Deprivation and satiation are the classic examples. Painful stimulation, being too hot or too cold, and lack of sleep are other common ones.

Discriminative stimuli: signalling a history

Michael (1982) described an SD as a stimulus condition that, given the current effectiveness of a type of reinforcement, increases a response because the stimulus has been correlated with that response being reinforced.

Put simply: in the presence of the SD, this behavior has paid off before. In its absence, it has paid off less or not at all.

Example: a child asks for a biscuit when Grandma is in the kitchen, but not when Dad is, because Grandma has said yes and Dad hasn't. Grandma is an SD for asking. She doesn't make biscuits any more valuable. She signals that asking works.

Two test questions

When a scenario describes something that happened before the behavior, ask:

1. Did it change how much the consequence is worth right now? If yes, it's an MO. A long, hot walk makes a cold drink worth more.
2. Does it signal that this response has been reinforced here before? If yes, it's an SD. A vending machine with its light on signals that putting money in has produced drinks before.

A useful check: remove the reinforcer's value and see what happens. If someone has just finished three bottles of water, the vending machine light (SD) won't evoke much buying. The SD only works when an MO makes the consequence valuable.

They work together

Poling and colleagues stress that MOs and SDs are distinguishable but interactive:

• An SD evokes behavior only when a relevant MO is in effect. A restaurant sign has little effect just after a big meal.
• SDs determine which response an MO produces. A hungry child asks for "chips" from one grandparent and "French fries" from another, depending on who has reinforced which word.

In practice, a scenario often contains both. The question is which one the item is asking about.

Common mix-ups

• "The teacher said 'clean up' and the child cleaned up" is an SD question, not an MO question, as long as nothing in the scenario changed the value of the consequence. The instruction signals that cleaning up has been reinforced in that context.
• "The child skipped breakfast and is quicker to work for snacks" is an MO. Skipping breakfast changed the value of food, not the history of reinforcement.
• Abolishing operations are MOs too. "Satiation reduced responding" is about value, so it's an MO, not a missing SD.
• Don't decide from the word "before". Both come before behavior. Decide from what the event does: change value or signal past reinforcement.
• Escape from tasks has MOs too. Hard or long demands can make escape more reinforcing. In function-based scenarios, the demand can act as an MO for escape-maintained behavior.

Practise it

For each antecedent in a practice question, write "value?" or "history?" next to it before you answer. Over a few dozen questions, the distinction becomes automatic.

The lessons on B.16: motivating operations and B.17: MOs vs stimulus control cover both in depth. The free diagnostic shows how you're doing in B. Concepts and Principles overall.

FAQ

What is the difference between an MO and an SD? An MO changes how effective a consequence is right now, and so how often the related behavior occurs. An SD evokes a response because that response has been reinforced in its presence before.

Is an establishing operation the same as a motivating operation? An establishing operation is one kind of MO: it makes a consequence more effective. An abolishing operation is the other kind: it makes a consequence less effective.

Can the same stimulus be an MO and an SD? A single event can do more than one thing, and the two often act together. In a scenario, ask what the event is doing to the behavior in that moment: changing value, or signalling a history of reinforcement.

Is "deprivation" always an MO? Deprivation of an effective reinforcer is the textbook example of an establishing operation, because it increases that reinforcer's value.

Sources

• BACB, BCBA Test Content Outline (6th ed.): https://www.bacb.com/wp-content/bcba-outline-6thEd (tasks B.16 and B.17)
• Poling, A., Lotfizadeh, A. D., & Edwards, T. L. (2020). Motivating operations and discriminative stimuli: Distinguishable but interactive variables. Behavior Analysis in Practice, 13(2), 502–508: https://pmc.ncbi.nlm.nih.gov/articles/PMC7314879/ (value-altering and behavior-altering effects, SDs mediating MOs, interaction examples)
• Michael, J. (1982). Distinguishing between discriminative and motivational functions of stimuli. Journal of the Experimental Analysis of Behavior, 37(1), 149–155: https://pmc.ncbi.nlm.nih.gov/articles/PMC1333126/ (definition of the discriminative stimulus, two effects of establishing operations)
• Laraway, S., Snycerski, S., Michael, J., & Poling, A. (2003). Motivating operations and terms to describe them: Some further refinements. Journal of Applied Behavior Analysis, 36(3), 407–414: https://pmc.ncbi.nlm.nih.gov/articles/PMC1284457/ (motivating operation as the umbrella term)