ABA glossary
S-delta
Also called SΔ, S-Delta
Definition
An antecedent stimulus in whose presence a response has not been reinforced, so the response becomes less likely when that stimulus is present. Written SΔ.
In plain words
An S-delta is a "not now" signal learned through experience. If a behavior never pays off when a certain person, place, or object is present, the behavior drops off in that situation. In discrimination training, every trial where the learner responds to the wrong card or the wrong instruction is an S-delta trial: responding does not earn reinforcement. An S-delta is not a punisher. It does not make anything unpleasant happen; it only signals that reinforcement is unavailable.
Example from a session
Grace, 7, often interrupts her teacher. The teacher wears a red lanyard while running small groups and does not respond to interruptions then; without the lanyard, she answers Grace. After a few weeks Grace rarely interrupts when the lanyard is on. The lanyard has become an S-delta for interrupting. As the plan directs, the RBT who supports Grace in class responds the same way, so the discrimination stays clear.
For BCBA candidates and supervisors
S-deltas are created through differential reinforcement: the response is reinforced in the presence of the SD and placed on extinction in the presence of the SΔ. Multiple schedules use this to teach when a request will be honored (for example, a green card for "attention available" and a red card for "not now"), which helps thin reinforcement after functional communication training. An S-delta also differs from a discriminative stimulus for punishment (SDp): both lower responding, but through different histories.
Often confused with discriminative stimulus, discriminative stimulus for punishment
An SD signals that a response will be reinforced; an S-delta signals that it will not. An S-delta is also not an SDp. In an S-delta's presence, the response simply has not paid off (extinction). In an SDp's presence, the response has been punished. "Nobody answers when the lanyard is on" points to an S-delta; "she gets a reprimand when the lanyard is on" points to an SDp.
Exam tip
Look for a history of no reinforcement in the presence of a specific stimulus, followed by less responding when that stimulus is present. "Dad never buys candy, so the child stops asking Dad" describes Dad as an S-delta for asking.
Can you spot S-delta in a scenario?
Practice BCBA B.12 with exam-style questions and instant feedback.