What is a Discriminative Stimulus in ABA Therapy?

In the wide world of autism, the many acronyms can be overwhelming. ABA, ASD, BCBA, OT, RBT, SLP, and the list goes on. When you’re observing one of your child’s Applied Behavior Analysis (ABA) therapy sessions, you may hear the therapists use the term ‘SD’ and wonder exactly what they’re talking about. SD, or discriminative stimulus, is formally defined as “a stimulus in the presence of which a particular response will be reinforced” (Malott, 2007).

The Basics of SD
To illustrate SD in more straightforward terms, imagine a child is shown cards with four different colors listed:

If the ABA therapist asks them to point to ‘Purple’ and the child correctly points to the purple box, then they will receive positive reinforcement from the ABA therapist, such as the therapist saying “Great job!” In this example, the SD is the purple box. If the child incorrectly picks the yellow box, then they will not receive positive reinforcement from the therapist. In this example, the therapist is looking for the one correct answer among three other incorrect answers.


SD in the context of social skills

Once the child has established a basic understanding of SD, then they would work on applying this concept in a more advanced manner. In the context of ABA therapy can use an SD to build appropriate behaviors in a social context, such as interacting with classmates during school or in the community.

This method can be particularly helpful for children who are on the autism spectrum and have a goal of developing stronger social skills throughout the course of their ABA therapy. In the context of a social interaction, the SD would be a classmate waving to the student. This may also be called a social cue. The goal would then be for the child who is on the spectrum to respond appropriately (e.g. saying “Hello!” or waving back). The subsequent reinforcement in this example would be the classmate asking them to go play with trains.

Why is SD important in ABA therapy?
Social skills are a crucial part of childhood development, and while they come easily to some children, many children who are on the autism spectrum struggle with the social aspect of school. This means that responding to a discriminative stimulus does not come naturally and may require modeling and practice with an ABA therapist. Throughout the course of ABA therapy, children can build appropriate responses to SD, which can result in more positive social interactions with classmates, family, and new acquaintances in the community.



Malott, R. (2007). Principles of Behaviour. New Jersey: Pearson Prentice Hall.