Negative Discriminative Stimulus (Symbol: S’ or S-): An Overview
Discrimination learning is a fundamental component of classical conditioning, also referred to as Pavlovian or respondent conditioning (Bouton, 2004). Discrimination learning involves a subject learning to distinguish between two stimuli, typically referred to as a “conditioned stimulus” (CS) and an “unconditioned stimulus” (US). The CS is associated with the US, and as a result, an organism’s behavior is changed in response to the CS. While most discrimination learning studies focus on the CS, the presence of a “negative discriminative stimulus” (S’ or S-) is also critical for learning to occur. This article provides a comprehensive overview of the negative discriminative stimulus and its role in discrimination learning.
Definition
The negative discriminative stimulus (S’ or S-) is a stimulus that is presented in the absence of the US. It serves to indicate that the US is not present, and therefore, no reward or reinforcement will be given (Blough, 1982). S’ is critical for discrimination learning to occur, as it informs the subject that the US is not present and that no reinforcement is available. Without S’, the subject has no way of knowing that the US is not present, and thus, discrimination learning cannot occur.
Functions
The primary function of S’ is to inform the subject that the US is not present and that no reinforcement will be given. In doing so, S’ serves as an inhibitory cue, and thus, it can be used to modify behavior (Blough, 1982). For example, S’ can be used to inhibit a response that has been reinforced in the past (e.g., a lever press). Additionally, S’ can be used to modify the behavior of an organism in a more general sense. For example, S’ can be used to teach an organism to avoid certain stimuli or behaviors that may be associated with the US.
Behavioral Effects
The presence of S’ has a number of effects on behavior. First, S’ can be used to inhibit a response that has been reinforced in the past. For example, if a lever press is associated with a reward, the presence of S’ can be used to inhibit the lever press (Blough, 1982). Second, S’ can be used to modify the behavior of an organism in a more general sense. For example, a subject may learn to avoid certain stimuli or behaviors if those stimuli or behaviors are associated with S’ (Blough, 1982). Finally, S’ can be used to teach an organism to respond to novel stimuli. For example, if a subject is presented with a novel stimulus (e.g., a light) in the presence of S’, the subject may learn to associate the novel stimulus with S’ and, as a result, avoid the stimulus (Blough, 1982).
Conclusion
The negative discriminative stimulus (S’ or S-) is a critical component of discrimination learning. It serves to inform the subject that the unconditioned stimulus is not present and that no reinforcement will be given. Additionally, S’ can be used to modify the behavior of an organism in a number of ways, including inhibiting a response that has been reinforced in the past and teaching an organism to respond to novel stimuli. As such, S’ is an important component of discrimination learning, and it is important to understand its role in learning.
References
Blough, D. S. (1982). Negative Discriminative Stimulus. In M. R. D. Segal (Ed.), Encyclopedia of Learning and Memory (pp. 205-212). New York: John Wiley & Sons.
Bouton, M. E. (2004). Context and Behavioral Processes in Extinction. Learning & Memory, 11(3), 485-494.