Talk the Talk: Discriminative Stimulus

Talk the Talk: Discriminative Stimulus

Aspects of the environment, like the behavior of others, signs, specific sounds, or even smells, can have a profound effect on people’s behavior. The presence or absence of certain environmental cues can predict the consequence of a particular behavior.    

For instance, imagine a woman is walking through her neighborhood sees a man unloading boxes from a moving truck. She wants to introduce herself but is unsure how he will respond. He might want to continue unloading boxes, so he can finish moving into his new home as soon as possible or he might want to take a break and chat with his new neighbor. As the woman gets closer to his house, she makes eye contact with the man, and he smiles and waves. Based on his behavior, the woman decides to stop and introduce herself.    

In the example, the woman was able to predict the outcome of introducing herself to her neighbor based on his behavior. Based on her previous experience in similar situations, people who smile and wave are likely to respond well to social greetings. From a behavior analytic viewpoint, the neighbor’s behavior (i.e., smiling, waving) was a cue that a social greeting was likely to be reinforced. In ABA that type of cue is referred to as a discriminative stimulus or SD (pronounced ess-dee).  

Technically speaking, a discriminative stimulus, or SD, is an aspect of the environment whose presence or absence signals the availability of reinforcement contingent upon the occurrence of a particular response or behavior.  

Described another way, it is a cue in the environment that signals that a specific behavior will be met with reinforcement. See the example below.

The woman asks the learner to find the number 6 within the array. If the learner selects the card with number 6 on it, they will contact reinforcement. If the learner selects any other number, they will not be given the reinforcer. Thus, the card with “6” on it signals the availability of reinforcement and is the SD. All the other cards signal that reinforcement is not available if they are selected. This is referred to as an S-delta (S). Stay tuned for more on S-deltas in a future post! 

Another common discriminative stimulus is a traffic light. A green light can act as an SD for the behavior of applying pressure to the gas pedal. This specific behavior is then reinforced by decreasing the amount of time it takes to get to the destination. A red light can act as an SD for the specific behavior of stepping on the brake pedal. This of course is reinforced by avoiding an accident or traffic citation.  

A discriminative stimulus does not signal availability of reinforcement for all behavior, only specific behavior. For example, a green traffic light is not an SD for pressing the brake pedal. In fact, a driver may experience punishment for engaging in that behavior if it causes an accident or other drivers begin honking their horns. 

The world is complex, which means people may have to respond to several environmental cues, often simultaneously. For example, in addition to identifying the color of the traffic light, a driver needs to identify the behavior of other drivers and pedestrians. These complexities will be discussed in future posts.