Stimuli and Discriminative Stimuli (SD)



(plural: Stimuli)

·       Anything that a person can experience through their senses. A stimulus may be seen, heard, smelled, tasted, or felt.
Neutral Stimulus (NS) ·       A stimulus which has not been associated (paired) with a specific response.
Discriminative Stimulus

(SD )

·       A stimulus that controls the probability of a response

·       When the SD is present, there is the possibility of reinforcement.

·       When the SD is present, we emit a behavior (response) because of the consequence, there is a higher chance of that behavior being reinforced than an alternative behavior.

S- Delta


·        A stimulus which does not lead to reinforcement (nor punishment).



  • Responses have been reinforced in the presence  (and not in its absence) of a specific stimulus  tend to occur more often when that stimulus is present. This process is known as Operant Conditioning.
  • Behavior is under stimulus control when the presence of an SD affects the probability of the behavior.
  • Stimuli affect people in different ways. A stimulus that one person finds aversive, like anchovies on pizza (S-), another person may love (S+).
  • An SD can be an instruction, a trigger, a cue. Any antecedent stimulus could be an SD.
  • Just because an SD is present, the response is not guaranteed. The SD indicates the availability of reinforcement. Ultimately one chooses whether to engage in a behavior to get that reinforcer.


  • A phone is a stimulus. When my phone rings it is an SD for the response of answering. If I have my phone on silent and it begins to flash, that is an SD for the response of answering as well.  When my phone beeps twice, that is an SD for me to look at my phone because I know that there is a new text message. The SD set the stage for me to exhibit those behaviors. Without an SD there would be no inclination for me to check my phone (being an introvert, I would not want to initiate conversationJ).
  • Percy tells Annabeth “Give me the pen”. Annabeth has never heard this expression before and does not know what a “pen” is. The instruction “Give me the pen” is a neutral stimulus (NS). It has no meaning to Annabeth. Percy repeats the instruction and immediately points to the pen (Bonus: what type of prompt is that?). With the help of Percy’s prompt, Annabeth picks up the pen and hands it to Percy. Now, when Percy says “give me the pen” (SD ), Annabeth will give him the pen because she enjoys the praise and attention from Percy. One day Percy asks “Give me the sword”. Annabeth looks around and sees two stimuli, the pen and an unknown item (NS). She knows the “pen” is not what Percy wants, so when Percy says “Give me the sword” the pen is an S-delta; it will not lead to reinforcement. Annabeth, being a great problem solver, knows that “Give me….” is an SD for her to hand something to Percy. She hands him the unknown item and Percy smiles and tells her how great she is. Annabeth has learned that the neutral stimulus is a “sword” and that “give me the sword” is an SD because if she gives him the sword it leads to reinforcement (smile and praise).