Stimulus discrimination refers to the ability to identify a specific stimulus and respond in a specific way, while also discerning that it is different to similar but different stimuli.
The concept of stimulus discrimination comes from the story of Pavlov’s dog. When the dog heard the sound of a bell, it was given food shortly afterward. After repeating the pairing of the bell with food several times, the dog “knew” that the sound of the bell predicted the presence of food.
Definition of Stimulus Discrimination
Stimulus discrimination (not to be confused with discriminative stimulus) is a concept from the theory of behaviorism. It occurs when you respond to one specific stimulus with a specific action. The person (or animal!) will respond only to that stimulus and not to others.
For example, Pavlov’s dog started to salivate when it heard the sound of a bell, but it did not salivate in response any other sounds.
The key to learning stimulus discrimination is repetition. In a very early study, researchers conditioned a dog to salivate when it saw a circle. The dog also salivated when it saw an ellipse or oval (this is known as stimulus generalization leading to a uniform conditioned response).
So, the researchers began showing those shapes but not giving the dog food. Eventually, the dog would only salivate when it saw a circle, but not an ellipse or oval.
Examples of Stimulus Discrimination
1. The Art of Wine Tasting
Short Description: Learning to differentiate between different types of wine takes a lot of repetition and practice.
As it turns out, the art of wine tasting is not just about taking a sip from the glass and swishing it around the mouth. It also involves examining the color and aroma of the wine.
If you are interested in becoming an expert in wine, it will take considerable time. At first, when you look at several different glasses of wine, you might not be able to tell the difference. Similarly, if you were to take a whiff from each glass, they might all smell the same to you.
However, with some guidance and instruction from an expert, you would learn how to distinguish among the various aromas and visual characteristics. Over time, it would be easy for you to identify and describe the differences. This is how stimulus discrimination applies to wine tasting.
2. Tuning an Instrument
Short Description: Tuning a guitar or piano takes time. Repetition and practice will help your ear to learn to differentiate between small sound differences.
Tuning a guitar or a piano requires a “good ear.” In fact, professional musicians will spend a significant amount of time tuning their instruments before a show or studio session.
With multiple guitar players in a band together, one will strike a chord and the other will listen carefully, and then make adjustments to match the pitch and tone. This is a process that can take several minutes per string.
Of course, when first learning how to play the guitar, it will be quite difficult to distinguish those sounds. It takes a lot of repetition to be able to identify one pitch from another. Eventually, stimulus discrimination will develop.
3. Tonal Languages
Short Description: Tonal languages like Mandarin have words that mean different things depending on your tone of voice. Learning what tone to use to convey the correct meaning requires repetition and practice.
Learning a tonal language requires a good ear. The most well-known tonal language is Mandarin. There are four tones in Mandarin and it takes quite a bit of time to be able to tell them apart.
However, after hearing the tones over and over again, your ability will improve. This is sometimes called “training your ear”. In a sense, it is exactly that. With a lot of repetition, it is possible that your auditory senses will be able to make finer and finer distinctions between the different tones.
Distinguishing between one tone and another is a perfect example of stimulus generalization as it applies to language learning.
4. Cognitive-Behavioral Treatments
Short Description: Some cognitive-behavioral treatments are designed to train people to interrupt their own stimulus generalization (or, indeed, response generalization) and, instead, to discriminate between different stimuli and contexts.
Various phobias and even post-traumatic stress disorder are often treated with techniques from cognitive behavioral therapy. Fear from an initial situation or event can begin to generalize to similar situations. This can be quite debilitating for people.
An essential component of treatment involves getting the person to recognize the differences in the situations that trigger a fear response and the initial event.
Patients are instructed on how to focus on aspects of the triggering situation that are dissimilar to the initial event.
This is a very rational approach. In a sense, it is training the brain to distinguish between one situation and another. In other words, the patient is being taught how to use stimulus discrimination.
5. Brand Differentiation
Short Description: To become a successful brand, you need to be able to differentiate your brand from others on the shelf. Through repetitive advertising, brands train consumers to be able to focus-in on your specific brand and block out all others.
Successful companies have devoted considerable time and money on building their brand. The image of a brand is everything in most industries.
Once has a brand has chosen upon a name, tagline, and color scheme, they go to work training their audience to associate the ‘good taste’ with the brand.
Thus, brands come up with advertising gimmicks like “finger lickin’ good”, “the happiest place on earth”. and “just do it” which are branded phrases designed to make their brand stand out as a unique ‘stimulus’ associated with quality and taste.
6. Dog Training
Short Description: When we train a dog to understand the difference between “sit” and “roll”, we have successfully taught the dog to discriminate between two stimuli.
Most people will train their dog using verbal commands. Of course, dogs can’t speak or understand any human language when they are born.
So, when the owner uses commands such as “sit” or “stay”, how can the dog understand the difference? Those two sounds are very similar. The answer is simple; though the process of stimulus discrimination.
In the beginning of training, the dog will not be able to distinguish between the two auditory stimuli. However, by repeatedly pairing one word with one action, the dog will eventually learn.
The owner may have to help the dog a bit by gently moving them into a sitting position while repeating the command. With enough repetition, the dog will eventually learn that one sound means sit, and the other sound means stay.
7. Eyewitness Testimony
Short Description: Witnesses need to be able to demonstrate their ability to discriminate between stimuli (i.e the facial features of criminals in a police line-up) in order to be seen as reliable.
Over the last 40 years there has been considerable research in psychology on the accuracy of eyewitness testimony. As science shows, there is a multitude of factors that affect accuracy.
One key finding is that people are much better at distinguishing the facial features of people in their own racial group than in other racial groups. This is known as the cross-race effect (CRE).
From a stimulus discrimination perspective, it makes sense. People spend more time interacting with members of their own racial group. Therefore, they will have developed more accurate stimulus discrimination.
Unfortunately, in the case of criminal investigations and trials, the inaccuracy of stimulus discrimination of people in other racial groups can lead to severe consequences.
8. Police Training
Short Description: When people train to be SWAT police officers, they need to repetitively practice being able to discriminate between threats with a gun and everyday bystanders, so they have this ability when in an active shooter situation.
Being in a live scenario involving a police or military situation is another example of the value of stimulus discrimination. Law enforcement and military personnel sometimes undergo training that involves video simulations and shoot houses.
The training involves presenting trainees with different situations similar to what they may encounter in the field. Of course, in the field, there are both dangerous individuals and innocent civilians.
Learning to discriminate the silhouette of someone with a firearm from a silhouette of a mother holding her phone can be quite difficult. Training helps develop an almost reflexive reaction to a stimulus so the officer or soldier makes an accurate judgment.
By allowing personnel to practice shooting at the right target in the safety of a simulation can replace years of in-the-field training. It can also save lives.
9. Reading Ultrasounds
Short Description: Ultrasound professionals need to be trained, over a long period of time, to differentiate between different signals on an ultrasound, and to identify which are normal and abnormal.
Ultrasound is an imaging technique that uses soundwaves to create images of what is inside the body. An ultrasound may be administered for a variety of reasons. The most common reason is to look at a developing baby in the womb.
Interpreting an ultrasound is nearly impossible unless you have had sufficient training and years of experience. The images are only in black and white, they’re blurry, and there can be a lot of movement.
In fact, learning how to distinguish between bones and tissue and other elements can take up to two years of training. In this example, stimulus discrimination takes a long time to develop.
10. Landmine Detection
Short Description: Animals are trained to be able to sniff out landmines but ignore scrap metals, in order to help find and diffuse mines in former conflict zones.
In some parts of the world, land mines are a significant danger. For example, there may be four to six million landmines and other unexploded ordnance in Cambodia. The country has one of the highest amputee rates in the world.
In one unique endeavor, APOPO, a Belgium nonprofit, has figured out a way to train rats to sniff out the mines.
The rats are trained to distinguish between the smell of different metals and a chemical compound found in explosives. This means that they will ignore scrap metal and only respond to landmines.
The training process takes about nine months. The trainers present different aromas to the rats, but only reward them when the odor comes from the chemical compound found in explosives. So, when the rats are in the field, they will only react when they detect that odor.
11. Sniffer Dogs at the Airport
Short Description: Sniffer dogs are taught to differentiate between different smells so they can identify people who are carrying illicit substances.
Airport sniffer dogs are specially trained dogs that are used to detect explosives and other illegal substances at airports. The dogs are usually Belgian Malinois or German Shepherds, as these breeds have a strong sense of smell.
The training process is very intensive, and it often takes up to two years for a dog to be fully qualified.
The dogs start by being taught basic obedience commands, and then they progress to more advanced training exercises. These exercises involve teaching the dog to identify specific smells, such as explosives, and to alert their handler when they detect them. Here, they are explicitly being trained in stimulus discrimination skills.
Short Description: Archaeologists need to be able to identify areas of a landscape that would have a high likelihood of buried relics and need to know the difference between different types of cultural artifacts to identify the context of the relics that were dug up.
In archaeology, the archaeologist will dig up a lot of old artifacts, and need to know the differences between each, in order to accurately and efficiently identify the significance of a dig location.
For example, an archaeologist in North America might dig up an arrowhead. The shape and size of the arrowhead can help the archaeologist to identify the era of the dig site.
Similarly, as an archaeologist walks through a field, they need to be able to identify potential cultural sites. They might look for a shelf halfway up a hill where people might have stopped to light a fire, or a particular spot along a river’s edge that would have been a likely place for camping.
Related Study Guide: Weber’s Law (Which argues that larger stimuli are harder for discrimination than smaller ones)
Being able to respond to one stimulus, but not all other similar stimuli, allows us to develop many advanced skills. It can take a considerable amount of time to develop stimulus discrimination.
However, over time and repeated exposure, it is possible to learn to distinguish the finer nuances of many stimuli. The essential element is that it takes numerous, sometimes hundreds of repetitions to hone the skill.
Stimulus discrimination plays a key role in tuning musical instruments, eyewitness testimony, military training, and the medical field. It is also an important element in treating phobias and PTSD, as well as landmine detection.
Brigham, J. C., Bennett, L. B., Meissner, C. A., & Mitchell, T. L. (2006). The influence of race on eyewitness memory. In R. Lindsay, D. Ross, J. Read, & M. Toglia (Eds.), Handbook of eyewitness psychology: Memory for people (pp. 257-281). Mahwah, NJ: Lawrence Erlbaum.
Ehlers, A., Clark, D. M. (2000). A cognitive model of posttraumatic stress disorder. Behaviour Research and Therapy, 38, 319-345. doi: https://doi.org/10.1016/s0005-7967(99)00123-0
U.S Department of Health and Human Services. (n.d.). Ultrasound. https//www.nibib.nih.gov/science-education/science-topics/ultrasound
Dr. Chris Drew is the founder of the Helpful Professor. He holds a PhD in education and has published over 20 articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education. [Image Descriptor: Photo of Chris]