Motivating Operations versus Discriminative Stimuli - What is the Difference and Why is it Important
Updated: Feb 28, 2019
In my last blog, I reviewed the basics of motivating operations. My hope is that after reading it, the concept of unconditioned motivating operations (UMOs) is now clear to everyone. Before stepping into the realm of CMOs, I am going to first review the differences between MOs and discriminative stimuli (SDs). Many may think this is a simple discrimination, but I have found that it is not. Let’s start with the flow chart that we used in the UMO discussion:
MO ⇒ SD ⇒ Behavior ⇒ Consequence
Food Deprivation ⇒ Light On ⇒ Push Bar ⇒ Get Food Food Deprivation ⇒ Light Off ⇒ Push Bar ⇒ No Food
In this classic experiment, the UMO is food deprivation and the SD is the light. If we were to run this experiment multiple times, we would find that in the “Light on” condition, the animal would learn to push the bar in order to get food. Alternatively in the “Light off” condition, the “pushing bar” behavior would tend to not occur.
The light being on functions as an SD, signaling that reinforcement is now available if certain behaviors are performed. The light being off functions as an Sdelta, signaling that reinforcement is not available for those same behaviors. It is important to note that in both conditions (SD or Sdelta) there is no change in the UMO. It stays the same no matter any change in the SD.
So, to get down to brass tacks: SDs are antecedent stimuli that have been associated with the availability or non-availability of reinforcement in the past. In our example, the association created is between “light-on” of “light-off” and food availability.
In order to discriminate an SD from an MO there are two tests that you can do:
Test # 1:
1. Is the consequence more available (SD) or more valuable (MO) following a period of deprivation? a. More available? No. Being food deprived did not make the food any more available. So it is not an SD. b. More valuable? Yes. Being food deprived did make food more valuable So the answer is that food deprivation is an MO.
1. Does the antecedent event meet both requirements of the definition of an SD? a. In its presence, is reinforcement available for certain responses? Yes, if you are food deprived, reinforcement is available for certain responses (bar- push) b. In its absence, is reinforcement not available for those responses? No. If you are not food deprived, reinforcement is still available for certain responses (bar-push).
So the final answer is that food deprivation is an MO.
In regard to the “light-on” condition we can use test #2 to determine if is an SD: a. In its presence, is reinforcement available for certain responses? Yes b. In its absence, is reinforcement not available for those responses? Yes
Therefore, the “light-on” condition is an SD.
A more complex example comes when we look at negative reinforcement and the consequence of escape. Let’s imagine that we are looking at this typical behavior chain:
Aversive Demand presented ⇒ Tantrum ⇒ Escape from demand
So is “demand presentation” an SD or a MO? Here’s how I use our two tests to answer this question:
1. Is the consequence more available (SD) or more valuable (MO) following a period of deprivation? More available? No. Having a demand presented did not make escape any more available. So it is not an SD.
More valuable? Yes. Demand presentation did make escape more valuable So the best answer so far is that Demand presentation is an MO.
1. Does the antecedent event meet both requirements of the definition of an SD? a. In its presence, is reinforcement available for certain responses? Yes, if the demand is presented, reinforcement (escape from that demand) is available for certain responses (tantrum)
b. In its absence, is reinforcement not available for those responses? No. If the demand is not presented, reinforcement (in the form of escape from that demand) is not available for certain responses (tantrum). In this case, demand presentation is an MO.
So, why is all this important for behavior analysts to understand?
In simple situations, such as Skinner’s pigeon experiments, understanding and defining the effects of SDs and MOs is rather straight-forward. But once we begin working with humans in the real world, these variables are not as clear-cut. I have found that when I provide supervision to BCBAs and BCBA students, in complex cases there is a general tendency to define almost all antecedent events as SDs and to neglect the concept of MOs.
Now, why is that? I’m not 100% clear, but I believe it has to do with our tendency to think that we, as behavior analysts, in the perfect world, can control all aspects of a person’s environment. Because complex MOs are more difficult to “see” and are related to internal states, we tend to look for SDs and neglect MOs.
Next time, we will begin the discussion of conditioned motivating operations (CMOs) and see how learning, paired with UMOs can explain how many seemingly inexplicable behavior develops and is reinforced over time.