What You Need to Know About Weber’s Law

Psychology has always been a study that constantly asks a single question: Why? Why do we think this way? Why do we feel this way? Why do we behave this way? In a discipline so deeply linked to philosophy, it should come as no surprise that many theorems in psychology are still unanswered questions. There is only so much that can be empirically proven about human nature. However, with the rise of scientific and technological advancement, the sub-field of neuropsychology is in a better place than ever to find answers to some of the more nuanced psychological theories, such as Weber’s law.

As it stands, Weber’s law is currently enjoying a moderate amount of experimental attention in neuropsychology. Neuropsychologists are trying to pin down how human neurons detect and process physical stimulation, and Weber’s law happens to be the most long-standing theory on this phenomenon in the entire study of psychology. So, what is this theory? We’ll break down what Weber’s law is, why the law is useful, and the key points of the law that make neuropsychologists so curious.

In the simplest terms, this theory is about human perception. Specifically, this theory tries to understand how humans can perceive even the slightest difference between two stimuli. This theory addresses each of the five senses –touch, taste, scent, sight, and hearing–and suggests that human perception is sharp enough to accurately distinguish between the smallest of differences.

In the Weber’s law theory, the “difference threshold” is the absolute smallest difference between two similar stimuli. Some neuropsychologists refer to this as “just noticeable difference”. In either case, the difference threshold grounds the theory with the caveat that the human mind can perceive the difference between two stimuli better depending on how close the comparison stimuli is to the original stimuli. Or in other words, we humans can distinguish between changes in stimuli even when two stimuli are very similar.

However, Weber’s law and human perception is challenged when the original stimuli is very intense. When the intensity of a stimuli is great, we have a harder time detecting changes after introducing another stimuli. This is the case for all five of the senses. If we are exposed to an intense stimulus, we are less likely not notice a subtle stimulus simply because the comparison between the two is too great. In this way, the difference threshold also suggests a blind spot in human perception.

This is a theory that can be very useful. In fact, we probably contend with this theory every day without noticing it much. Just like many theories in the broad field of psychology, humans are constantly proving or disproving the accuracy of theories. This law is no exception. Let’s look at some examples where Weber’s law is both present and useful.

The original proposal for this theory in 1834 was made on the basis of psychophysics, or the intersection between psychology and physics. For this new theory, the easiest way to test it was to use something that could be easily measured and recorded: weight.

Imagine you are holding a paperback book in your hand. You can obviously feel the heft of the book as well as the general size and shape. If we were to place another book of similar size, shape, and weight in that same hand, you would be able to detect the added weight. If we were to place another book that is slightly heavier or has a different shape in your other hand, you would be able to decide which book is lighter or heavier. Both are an example of the difference threshold.

However, if you were holding a box of books and we placed that paperback book on top of the box, you probably wouldn’t be able to detect the added weight. Why? It’s the perception blind spot in the difference threshold. Because the box of books is so heavy–making the stimulus intense–you are not able to detect the subtler stimulus.

We humans have an exceptional talent for detecting temperature changes. If you closed your eyes and we touched each of your arms with a piece of ice, you would be able to tell which piece of ice is larger because of how your skin would register a larger cold spot. But if we submerged your entire arm in ice water and then touched that arm with a piece of ice, you wouldn’t be able to register the smaller point of cold because of the intensity of your entire arm being cold thanks to that perception blind spot.

Temperature detection that is compromised can be dicey. When a body is exposed to cold for too long and hypothermia begins to set in, it is recommended that the body be warmed in small increments, starting with warm water and working up to body temperature water. Why? Simply because Weber’s law proves that the perception of temperature will be so drastically altered after the intensity of full-body cold that the body is unable to tell whether something is burning hot or not. In order to protect the skin, and to not shock the entire body system, victims of hypothermia are warmed gradually.

While we all might not have the sensitive palate of wine tasters, the average human taste bud can detect slight differences in the way something tastes. Imagine making two pots of chicken soup, but one pot has an added secret ingredient. In a blind taste test, people who try the two soups would be able to tell which of the soups has the added ingredient.

However, if the intensity of the flavors is very great, the taste buds will be so overwhelmed that they would be unable to detect additional flavors unless the additional flavor was drastically different. This is why it is recommended to drink cold milk or water after eating something very spicy–the stark difference between the milk and the spice can reset your taste buds.

The human ear is a highly sensitive thing. If we focus, we really can hear the most minute sounds from across a room, which is why we can eavesdrop on a juicy conversation in a crowded room without any problems. However, if we overwhelm the difference threshold with an intense original stimulus, the following stimuli will be harder to detect. This is why people have trouble hearing each other during concerts. The sound of the concert is so overwhelmingly loud that it is almost impossible to hear the person next to you even if they are shouting in your face.

Most humans actually have decent color perception because of the difference threshold. If we placed two red cards in front of you and asked you which card was more yellow, you would be able to point at the red-orange card with some ease. If we placed two blue cards in front of you and asked you which card was darker, you could point to the darker card without any trouble. If we placed two green cards in front of you and asked which is more vibrant, you would be able to pick the right card again. Human color perception is generally spot-on.

However, we run into some challenges when faced with light. The intensity of bright lights, such as the sun or a flashlight, shining in our eyes is so great that we can have trouble detecting weaker lights, colors, and even objects until our eyes adjust. This is another way in which the intensity of the original stimulus can undermine the difference threshold.

Human scent perception is fascinating. Not only are out olfactory senses tied directly into memory coding, but they also vary in sensitivity between human to human. Some people are able to detect the slightest differences between two similar scents, while others can only tell the difference between two different scents.

And just like every other sense, scent is also vulnerable to the blind spot in the difference threshold. If we doused a handkerchief in perfume, held it against your nose, and then asked you to try to smell anything else, you would find it impossible because of the intensity of the perfume.

Neuropsychologists continue to conduct research to try to understand how our sensory nerves detect stimuli and how that detection translates into perception in the human brain. These are the key points that they continue to come back to:

Neuropsychologists are trying to pinpoint how human perception is translated by the brain. One of the ways they do this is to study the brain through MRI scans while exposing volunteers to different stimuli. Some of this research has enabled neurologists to confidently isolate the portions of the brain that are responsible for sensory processing.

Although not talked about often, Weber’s law is a cornerstone of neuropsychology. As one of the most enduring psychological theories in the field, this law and the associated principles of the law continue to make the case for the sensitivity of human perception.

This theory overall suggests that human perception is sensitive enough to accurately distingish differences between two similar stimuli, with the exception of intense stimuli that overwhelm the senses.

Researchers continue to try to understand how the brain processes sensory information by using Weber’s law as a basis in experimentation.

Featured Image: Image by Mashiro Momo from Pixabay