The role of the barely perceptible difference in psychological experiments (2023)

The Just Noticeable Difference (JND), also known as the Difference Threshold, is the minimum level of stimulation a person will exertcan recognize50% of the time. For example, if you are asked to hold two objects of different weights, the difference you might feel would be the smallest difference in weight between the two that you could feel half the time.

The almost imperceptible difference applies toall the sensesincluding touch, taste, smell, hearing, and sight. It can be applied to things like brightness, sweetness, weight, pressure, and noise, among others.

It is important to understand the barely noticeable differenceabsolute threshold. While difference threshold, or simply the perceptible difference between two stimuli, means detecting differences in stimulation strength, absolute threshold refers to the lowest detectable stimulation force.

For example, the absolute sound threshold would be thisthe lowestVolume that a person can hear. The only noticeable difference would be the slightest.changeto the volume that a person could feel.

History of the JND Concept

The difference threshold was first described by a physiologist andexperimental psychologistcalled Ernst Weber and later expanded by the psychologist Gustav Fechner. Weber's law, sometimes known as the Weber-Fechner law, suggests that the perceived difference is a constant proportion of the original stimulus. However, we now know that the JND is not a constant but a variable.

Since only notable differences are measured

To measure sensory information and difference thresholds, scientists rely on responses from study participants. The measurements that scientists make depend on the sensory information they receive. For example, they may use decibels when measuring sound. When measuring heat, you can use joules.

The JND is usually determined byRunning various experimentsand then at the lowest levels that participants could detect at least 50% of the time.

neural activity

Our brain receives sensory information (such as light, sound, or taste) and our sense organs convert this information into electrical signals that are received by the brain.Therefore, measuring neural activity is another way for researchers to determine how much (and what kind of) sensory information a person is receiving.

In one study, researchers found that they could tell if someone was touching something sticky or not based on their neural activity.

stimulus intensity

The intensity of the stimulus may also play a role in the intensity with which people perceive the changes. When a light is very, very dim, people are more likely to notice smaller changes in intensity than if the same changes were made in brighter light.

For example, imagine that you are in a dark cinema. The lights in the house come on slowly and you immediately notice even a very small change in light intensity. After that, leave the theater and go outside, where the sun is shining brightly. If the same changes in light intensity are made outdoors, you may notice them less because the level of stimulation is much higher.

Examples of barely noticeable differences

Below are examples from everyday life where you can see the barely noticeable difference.

Weight

Imagine that you are a volunteer for apsychology experimentin your school. The researchers ask you to hold two small amounts of sand in each hand. An experimenter slowly adds small amounts of sand to one hand and asks you to say when you notice that one hand is heavier than the other. The smallest weight difference you can notice at least half the time is the barely noticeable difference.

klang

You are watching TV with your partner, but the volume is too low to hear anything. You ask your partner to turn up the volume. He presses the volume button twice, but still doesn't notice any difference in volume. Your partner presses the button two more times before you hear the volume increase.

Or: You are having a party in your apartment and the neighbor comes and asks you to turn down the volume of the music. You and your guests will immediately notice that the music is much quieter, but your neighbor won't notice any difference in volume because the change is below the difference threshold.

Tastes good

You volunteer for another psychological experiment at your school. This time, the experimenters put small amounts of sugar in a container of water and asked you to drink it. You will be asked to indicate when you notice the sweetness of the water compared to plain water. The smallest sweetness you can taste in half the time is the threshold difference.

heart

You dye your hair, but afterward the color remains the same as before. This is because you dyed your hair a similar shade to what you already had, and the color is not above the difference threshold.

Just a noticeable difference in marketing.

Marketers can use JND in many ways. For example, a company can determine the JND of a price point so that it can raise the price of a product so easily that people don't notice.

Companies often reduce the size of packages, such as boxes of pasta or cans of corn. They will intentionally decrease the size by an amount below the difference threshold so people won't notice that their favorite products have actually gotten smaller.

Reducing package sizes saves companies money, but is often considered an unethical practice: "tricking" consumers into buying their favorite products at the same (or higher) price, but unknowingly getting less.

Why only a noticeable difference matters

Only the notable differences are part of a field of study known as psychophysics. Psychophysics studies how physical stimuli in the environment affect and interact with mental processes. In other words, while scientists used to focus on measuring objective data, psychophysics allows them to measure subjective experiences as data.

JND is often studied in product development. For example, when manufacturing cell phones, companies measure the JND of the volume, so there are noticeable increases as the volume of the device increases.

Food producing companies also study the JND. For example, if a product tastes like green apples, the manufacturer needs to know the minimum amount of green apple flavor needed for most people to taste it.