Essential Reading
Read the conversation below between an RBT and their BCBA supervisor, which explains the concept of stimuli and stimulus classes:
RBT: Hi, I’ve been hearing about discriminative stimuli and stimulus classes in ABA. Can you explain the difference?
BCBA: Of course. In ABA, a stimulus is any event or situation that can be perceived by our senses — like something we see, hear, touch, smell, or taste. It plays a role in behavior change. Now, within stimuli, we have two important categories: discriminative stimuli and stimulus classes.
RBT: So, what’s a discriminative stimulus?
BCBA: A discriminative stimulus (SD) is a specific type of stimulus. It’s like a cue that tells the individual that if they perform a particular behavior in its presence, they’ll get reinforcement. For example, when a teacher says, “Raise your hand if you know the answer,” the teacher’s voice is the SD that signals reinforcement (like praise) for raising one’s hand.
RBT: Got it. What about a stimulus class?
BCBA: A stimulus class is a broader concept. It’s a group of stimuli that share similar characteristics and can evoke the same or similar responses. These stimuli might not look or sound the same, but they have common features that make them functionally equivalent in their effects on behavior.
RBT: Can you give an example to clarify the difference?
BCBA: Sure. If we teach a child to touch a red square when we say “Touch red,” then:
- The stimulus is the red square.
- The discriminative stimulus (SD) is the instruction “Touch red.”
- The stimulus class includes all red objects (red circle, red triangle, etc.) — because they all share the property of being red.
RBT: That makes sense. Understanding this helps with teaching and generalising skills, right?
BCBA: Exactly. Recognising SDs and stimulus classes helps us promote generalisation and design effective interventions. Let me know if you’d like more examples!
Further reading: Learning Behavior Analysis: B-2: Define and provide examples of stimulus and stimulus class
Optional Video
Watch this short video for an extra explanation of stimulus classes:
Conversation Exercise
Complete the Conversation Exercise with FRED, our AI-powered chatbot. This helps reinforce your understanding through guided questions.
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Click the conversation icon in the bottom right corner of your screen, or open FRED directly here.
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Reflection Exercise
After completing the reading, video, and conversation exercise, reflect on your learning using the prompts below. Your reflection should be:
- Between 100 and 500 words (about 5–7 sentences minimum)
- Written in your preferred language
- Expressed in your own words — do not copy text from chatbots, websites, or this course
You’ll receive an email copy of your reflection to aid your RBT exam preparation.
Click to view Reflection Prompts & Example
Reflection Prompts (use one or more):
- Summarize Key Concepts: What are the main ideas you learned about stimuli and stimulus classes?
- Define in Your Own Words: How would you explain these concepts to a colleague or parent?
- Importance and Connections: Why is it important to understand stimulus classes when teaching new skills?
- Practical Applications: Can you think of real-life examples where understanding stimulus classes would help you teach or support someone?
- Insights: What did you find surprising or particularly useful in the reading, video, or conversation with FRED?
Example Reflection:
Before this lesson, I thought a stimulus was just anything that triggers a behavior, but I didn’t realize how organized ABA is in classifying them. The distinction between discriminative stimuli and stimulus classes really helped me see how people learn to generalise skills across different situations. The idea of teaching someone to recognise all red objects as ‘red’ made it click for me. I also didn’t know that instructions themselves are stimuli. This makes me think about how carefully I need to present instructions when teaching new skills. The article and video made the concepts clearer and now I feel more confident identifying these in real sessions.
When you’re ready, submit your reflection below:
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