A neutral stimulus is a stimulus which does not innately evoke a response. Upon first encounter, the object or situation has no meaning so it does not elicit a response.
Later, if the stimulus becomes associated with something of meaning to us, then it moves from a neutral stimulus to a conditioned stimulus.
For example, if students hear a bell and it means nothing to them, they won’t respond (it’s a neural stimulus). But later, if it becomes associated with the end of school, it might get the students excited when they hear it (it’s become a conditioned stimulus!).
Neutral Stimulus Definition and Overview
The notion of a neutral stimulus is a key component of Pavlov’s (1927) theory of learning known as classical conditioning.
Classical conditioning explains how organisms learn by experiencing associations between different stimuli. When certain stimuli are repeatedly associated, then the properties of one transfer to the properties of the other.
For example, Pavlov demonstrated that a dog could be trained to salivate whenever it heard a bell. The bell itself started out as possessing no innate meaning. It certainly did not elicit salivation in the dog upon first encountering it.
However, because Pavlov jingled the bell just prior to presenting food, the dog began to salivate whenever it heard the bell.
The salivation evoked from food, which is innate, transferred to the sound of the bell.
There are several key terms involved in classical conditioning that are important to know in order to fully understand how the notion of a neutral stimulus fits.
- Unconditioned Stimulus (UCS): The UCS is a stimulus that naturally/innately triggers a response. Examples include: food and water, or biologically-based stimuli such fear-provoking loud noises or those related to reproduction.
- Unconditioned Response (UCR): The UCR is the response that is naturally triggered by the UCS. It occurs automatically and requires no learning through association. For example, food will automatically make an animal salivate. So, the salivation is referred to as the UCR.
- Conditioned Stimulus (CS): The CS is a stimulus that is initially neutral and does not automatically trigger any kind of response. However, because the CS has been associated repeatedly with the UCS, it too will trigger a response similar to the UCR.
- Conditioned Response (CR): The CR is the response that is triggered by the CS (i.e., neutral stimulus). The CR is nearly identical to the UCR.
The Acquisition Process in Classical Conditioning
Acquisition refers to the initial stage of learning when the UCS and CS are being paired. There are several factors that affect acquisition.
- Number of Pairings: Generally speaking, as the number of times the UCS and the CS are paired increases, the stronger the acquired behavior (CR). There is such a thing as one-trial acquisition, in which it only takes one pairing, but that only occurs in unusual situations.
- Intensity of the UCS: The greater the magnitude of the UCS, the stronger the response, up to a point. For example, if Pavlov only presented a small amount of food to the dog, then it would salivate less. As the amount of food increases, so does the response.
- Reliability of Pairing: The more times that the UCS and the CS are not paired, the longer it takes for acquisition to occur. The CS must have a predictive quality to it. The less reliable the pairing, the less predictive is the CS.
- Contiguity: The closer in time the CS is followed by the UCS, the quicker the acquisition process. Generally speaking, the quickest and most reliable acquisition will occur when the CS precedes the UCS by about half a second. Although there are some variations to this basic rule.
Neutral Stimulus Examples
- Coffee Beans: When humans first encountered the coffee bean, it had no inherent meaning. However, because it has been repeatedly associated with pleasures that come from consumption, it now has meaning.
- Paper Currency: The paper that represents currency is not inherently significant. It is just a piece of paper. It has attained its meaning because of its power to acquire goods and services.
- The Padaung Tribe: Females in the padaung tribe elongate their necks by wearing brass rings starting at an early age. The elongated neck is an example of a neutral stimulus that is today considered more attractive because of its cultural meaning.
- Letter Grades: Before attending school, the letters ABC had no intrinsic meaning. However, because they become quickly associated with levels of performance, each one begins to take on a meaning and significance…and supposed implications as to one’s level of intelligence and future earning potential.
- The Hypodermic Needle: The first time a human infant sees a hypodermic needle it has no meaning whatsoever. However, after it has been used one time, it takes on immediate meaning. The pain from the needle penetrating the skin means that the next time the infant sees the needle, they may experience intense fear.
- Musical Preferences: There may be some musical notes which are innately pleasing or aversive, however, a preference for a particular genre of music is a function of culture. For instance, being raised in a household of jazz-fusion musicians will lead to a preference for that genre. However, play that music to members of an Aboriginal tribe and their reactions may be quite different.
- Career Status: In many Western cultures, being a medical doctor is associated with great prestige. However, in some third-world cultures, where doctors are not well-paid, there is not so much admiration for the profession. Being a doctor in and of itself has no innate meaning; its status and prestige are culturally defined.
- Technology: Take an Apple iPad to a tribe in the Amazon that has had nearly zero contact with the outside world, and they might use it to chop food on. The item has no inherent meaning. However, take the same iPad to an impoverished but modern culture, and it will elicit immediate excitement.
- The Dog Leash: The first time seeing a leash, the household dog has no prior association with it, and therefore, it possesses no inherent meaning. However, after a few times of the family retrieving the leash before taking the dog for a walk, it takes on a very significant meaning. Now, even when a member of the family walks near the closet where the leash is kept, the dog starts getting excited.
- Precious Gems: There are many kinds of precious gems, and many are highly valued in the modern era. However, other than a pleasing appearance, they do not have near the intrinsic value as that ascribed to them by society. Without their association with jewelry and current price structure, they would barely be given a second thought when found on the ground centuries ago.
Application of the Neutral Stimulus: The Token Economy
A token economy uses tokens as rewards that can be exchanged for desired items or privileges. A token can be a small plastic chip or a stamp. The value of these stimuli is that they inherently have no real meaning to participants. However, because they are connected to receiving certain rewards, they acquire meaning.
Token economies are utilized in a wide range of settings, from psychiatric hospitals, to correctional facilities, to classrooms.
LePage et al. (2003) implemented a token economy in a psychiatric unit where patients could receive stamps for engaging in socially acceptable behaviors such as showering or keeping their appointments.
Those stamps could then be traded for snacks or movies. Or, stamps could be taken away for unacceptable behavior such as destroying property or getting into physical altercations.
The results indicated that at a 2-year follow-up, instances of patient-patient injury decreased by 48% and patient-employee injury decreased by 21%.
A literature review by Maggin et al. (2003) concluded that research on token economies in school settings did not meet evidence-based standards, but did provide supportive evidence regarding its effectiveness.
A meta-analysis by Soares et al. (2016) involving single-case applications found that token economies were more effective for ages 6-15 years old than ages 3-5.
The difficulty in examining the effectiveness of token economies is that they are often implemented according to different procedures. Each institution may follow different guidelines and provide varying degrees of quality training (Reitman et al., 2021).
Related Theoretical Concepts
- Stimulus Discrimination – When an organism has a response to one stimulus but not to another. Each stimulus does not trigger the same response. This is likely due to their significant differences in appearance or other distinctive characteristics.
- Stimulus Generalization – When an organism reacts to different stimuli in the same manner. The two stimuli may be similar in appearance or other characteristics.
- Response Generalization – When an organism reacts to the same stimulus in a variety of different ways. Usually, those reactions are in the same behavioral class and are similar.
- Habituation – When a stimulus no longer triggers a response. The organism is said to have habituated to the stimulus. For xample, the sound of a loud bell may be startling at first, however, over time, it does not create a startle response.
- Extinction – When a CS has been repeatedly presented without the accompanied occurrence of a UCS, over time the CS will cease triggering a response (i.e., CR).
- Higher Order Conditioning – When a two-step chain in the conditioning process occurs such that UCS1 is linked to a CS, then UCS1 is associated/linked with UCS2. Over time, UCS2 will trigger the unconditioned response by itself, even after UCS1 is no longer involved.
The neutral stimulus is incredibly powerful and flexible in use because it initially has no significance. Because it does not innately trigger a response in an organism or human being, it can be used in a variety of ways.
For example, psychiatric institutions and classrooms can implement a token economy that is based on the idea that tokens are initially neutral stimuli. However, they take on immense meaning in a token economy because they can be exchanged for desired objects or privileges.
Although initially meaningless, those chips and stamps begin to represent something that participants want.
Trying to accumulate tokens can then shape the behavior of participants in many constructive ways by increasing socially acceptable behavior and decreasing destructive actions.
LePage, J. P., DelBen, K., Pollard, S., McGhee, M., VanHorn, L., Murphy, J., … & Mogge, N. (2003). Reducing assaults on an acute psychiatric unit using a token economy: A 2‐year follow‐up. Behavioral Interventions: Theory & Practice in Residential & Community‐Based Clinical Programs, 18(3), 179-190.
Maggin, D. M., Chafouleas, S. M., Goddard, K. M., & Johnson, A. H. (2011). A systematic evaluation of token economies as a classroom management tool for students with challenging behavior. Journal of School Psychology, 49(5), 529-554.
Pavlov, I.P. (1927). Conditioned reflexes. London: Oxford University Press.
Reitman, D., Boerke, K., & Vassilopoulos, A. (2021). Token Economies. Handbook of Applied Behavior Analysis, 374.
Soares, D. A., Harrison, J. R., Vannest, K. J., & McClelland, S. S. (2016). Effect size for token economy use in contemporary classroom settings: A meta-analysis of single-case research. School Psychology Review, 45(4), 379-399.