difference threshold experiment

Just Noticeable Difference (JND) in Psychology: Examples & Definition

Charlotte Nickerson

Research Assistant at Harvard University

Undergraduate at Harvard University

Charlotte Nickerson is a student at Harvard University obsessed with the intersection of mental health, productivity, and design.

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Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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The difference threshold often referred to as just noticeable difference (JND), is the minimum amount of change required to be detected in a stimulus. The concept was first proposed by German psychologist Ernst Heinrich Weber (1795-1878).

• The difference threshold is the minimum difference in the intensity of two stimuli necessary to detect they are different. For example, two lights may be illuminated at the same time. The difference threshold is reached when an observer can tell that one is brighter than the other.
• Often defined as the difference for which the percentage of correct discrimination is 75%, though other percentages are sometimes used.
• The difference threshold allows experimental psychologists to understand the relationship between the physical intensity of a stimulus and people’s or animals’ perception of that stimulus. The smaller the difference threshold, the more sensitive someone is to changes in the quantity described by it.
• Difference thresholds are differentiated from absolute thresholds in that the former refers to the smallest difference that can be detected between two stimuli, while the latter refers to the minimum amount of change required to detect a stimulus.

Development of the Concept

The difference threshold, otherwise known as the just notable difference or the difference limen, is the smallest difference between two stimuli that can be consistently and accurately detected in experimental trials 50% of the time.

This concept describes the minimum amount by which a stimulus” intensity must be changed in order to produce a noticeable variation in the sensory experience of a participant in an experiment.

Ernst Heinrich Weber (1795-1878), a notable 19th-century experimental psychologist, observed that the difference threshold was related to the strength of the stimulus being used in a mathematical way.

The relationship between these two is called Weber’s law.

In other words, Weber’s law says that the size of the difference threshold — delta I — is in direct proportion to the original value of the stimulus.

For example, consider a scenario where a researcher gives an observer two spots of light, each with an intensity of 100 units.

Then the researcher asked the observer to increase the intensity of one of these spots until it was just noticeably brighter than the others.

If the brightness needed to yield this difference threshold was 110, then the observer’s difference threshold would be ten units.

Thus, the change in I needed to spot the difference over the original brightness is 0.1.

Using Weber’s law, the person conducting the experiment could now predict the size of the observer’s difference threshold for a light spot of any other intensity, so long as it was neither extremely dim nor extremely bright.

That is to say, if the Weber fraction for the change in brightness needed to be able to detect a change is a constant proportion equal to 0.1, then the observer would notice a change in brightness when a 1000-unit bright light became an 1100-unit light, or a 10000 unit bright light became an 11000 unit bright light (Ross, 1995).

This law can be applied to any of the senses. The difference threshold can apply across, say, brightness, loudness, mass, line length, and so on.

Although the size of the weber fraction varies across the medium that is being measured and groom observer to observer, the relationship tends to stay linear (Ross, 1995).

This mathematical relationship between what people perceive and some physical quantity is a feature of a field called psychophysics.

Psychophysics is a branch of psychology concerned with the relationships between physical stimuli and mental phenomena (Gescheider, 2013).

Say that someone held two weights in their hands and could make them heavier and heavier until they noticed that the mass of one was greater than another.

For example, someone may notice that a 100g and 125g mass differed at least 50% of the time.

According to Weber’s law, then, the difference threshold of this observer sensing the mass of these weights is 125g/100g or .25.

This means if the observer were holding a 1 or 10kg object in one hand, the object in the other hand would need to have a mass of 1.25 or 12.5kg, respectively, to feel heavier.

Similarly, the object would need a mass of .75 or 7.5kg to feel lighter than the 1kg object for that observer.

Similarly, consider a participant in an experiment who is asked to change the volume of a piece of music until they are able to hear that it is at a different volume.

If the original volume of the piece were 200 units, and the person needed to increase or reduce the volume by 100 units to hear a difference, then the difference threshold for that person hearing that piece would be 0.5.

So, if the music were playing at 30 or 500 units, they would need to change the volume to 45 or 750 units to hear a difference, respectively.

Taste and Smell

The difference threshold can also apply to senses that are not as commonly quantified as mass and sound, such as taste and perfume.

To imagine the first of these experiments, consider a scenario where someone is asked to eat saltier and saltier bowls of soup until they can perceive a difference in taste.

In a similar vein to before, the mass of salt needed to create a perceived difference in taste would be linear to the amount of salt originally in the dish.

In the case of smell, someone could be asked to discern the minimum difference in the quantity of perfume needed to perceive a difference in something’s smell in a similar manner, with a similar relationship.

Color difference

To further this idea of things that normally do not seem quantifiable, being quantified through the concept of the difference threshold, consider the differences between colors.

A scientist may be able to measure the differences between colored paint by the amount of each primary color it is composed of.

When testing a participant on their color perception, they may ask them to mix increasing, small increments of blue dye into a tub of red water until they notice a color difference.

As with the preceding examples, this difference threshold is constant.

So, if it took five drops of blue dye to perceptively change the color of a tub of water with 30 drops of red dye, the difference threshold for this color change would be 1/6.

Thus, if someone were to replicate the same experiment on a tub containing 90 drops of red dye, it would take about 18 drops of blue dye to perceiveively change the color of the water in the eyes of the observer about 50% of the time.

Absolute vs. Difference Threshold

One concept that is often confused with the difference threshold is the absolute threshold.

While the difference threshold involves an observer’s ability to detect a difference in stimulation levels, the absolute threshold refers to the smallest detectable level of stimulation.

Hence the word absolute.

For example, the absolute threshold for sound would be the absolutely lowest volume that someone can hear or detect.

Meanwhile, the absolute difference for sound would refer to the smallest difference in volume that that person could sense.

Another way that the absolute threshold is different from the difference threshold is that the absolute threshold is specific to each type of stimulus being measured. In contrast, the difference threshold can vary depending on the starting point of the stimulus.

For example, the absolute threshold for light might be the lowest level of brightness that someone could detect in a room, while the absolute threshold for sound might refer to the faintest noise that someone could hear.

However, the difference threshold for light would be the smallest increase or decrease in brightness that someone could notice, regardless of how initially bright or dim the room is.

Similarly, the difference threshold for sound would remain the same for a person, regardless of how loud or soft the noise they heard originally is.

Implications

The difference threshold has many implications for experimental psychology.

Namely, the concept of the difference threshold helps psychologists to understand why people do or do not sense the progression they are making as they move through an experiment.

For example, say that a researcher is conducting a study on people’s ability to taste different flavors of ice cream. In their experiment, the researcher might give each participant cups of ice cream with varying amounts of sugar.

The researcher would then have each participant rate the sweetness of each cup of ice cream.

If, after eating the ice cream, the participants discerned that one cup of ice cream was sweeter than another, the researcher could conclude that the difference in the amount of sugar in these cups was above the just noticeable difference.

However, if there was no significant, consistent difference between the ratings for the two flavors, the researchers would need to consider the possibility that the difference in the amount of sugar was too small to be noticed by the participants — that is, to surpass the difference threshold.

The difference threshold can also explain, for example, why someone may not be able to notice a gradual change in their weight, even though the change is happening over time.

The concept of a difference threshold can also be useful in marketing and advertising. For example, companies may take into consideration the difference threshold for brightness when choosing how to design their product packaging.

A company might want its products to stand out on store shelves, but it also does not want its products to be so bright that they become annoying or overwhelming.

By choosing a minimal discernable amount of brightness for their packaging, the company’s product can stand out from the display while minimizing the effects of visual irritation (Vojtko, 2014).

Gescheider, G. A. (2013). Psychophysics: the fundamentals . Psychology Press.

Helen, E. R., David, J. M., Ross, H. E., & Murray, D. J. (2018). EH Weber on the tactile senses. Psychology Press.

Miiller J, 1833-1840/1838-1842 Handbuch der Physiologie des Menschen (1833-1840, Coblenz: Holscher), translated in English by W Baly Elements of Physiology Vols 1 and 2 (1838 -1842, London: Taylor and Walton)

Ross, H. E. (1995). Weber then and now. Perception, 24 (6), 599-602.

Vojtko, V. (2014). Rethinking the concept of just noticeable difference in online marketing. Acta Informatica Pragensia, 3 (2), 204-218.

Difference Threshold: Definition and 10 Examples

Viktoriya Sus (MA)

Viktoriya Sus is an academic writer specializing mainly in economics and business from Ukraine. She holds a Master’s degree in International Business from Lviv National University and has more than 6 years of experience writing for different clients. Viktoriya is passionate about researching the latest trends in economics and business. However, she also loves to explore different topics such as psychology, philosophy, and more.

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Chris Drew (PhD)

This article was peer-reviewed and edited by Chris Drew (PhD). The review process on Helpful Professor involves having a PhD level expert fact check, edit, and contribute to articles. Reviewers ensure all content reflects expert academic consensus and is backed up with reference to academic studies. Dr. Drew has published over 20 academic articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education and holds a PhD in Education from ACU.

A difference threshold, also known as just noticeable difference (JND), is the smallest difference between two stimuli humans can perceive. In other words, it is the minimum degree of change that individuals can notice or detect. 

For example, a person may notice a slight temperature change in the room once it is at least a degree or two higher or lower than what they already feel.

The concept of difference threshold applies to all five senses: touch, taste, smell, hearing, and vision. Besides, it is useful for noting changes in luminosity, sweetness levels, weight or pressure range, and sound intensity variations.

This concept is widely used in psychology and marketing, as it helps explain how humans perceive environmental changes.

Definition of Difference Threshold

A difference threshold is the lowest amount of change that an individual can detect or recognize. It is measured in terms of how many “just noticeable differences” (JNDs) exist between two stimuli (Meilgaard et al., 2007) .

It also determines how sensitive a person is to certain stimuli and can be used to predict how often someone will react to a change.

According to Houston and colleagues (2013), a difference threshold is defined “as the level of difference that is detectable 50% of the time” (p. 84). 

For instance, if you were to hold two items of varying weights in each hand, the slightest weight difference between them that you could sense half of the time would be referred to as your “just noticeable difference.”

So, in simple terms, a difference threshold is the smallest perceivable difference between two stimuli.

10 Examples of Difference Threshold

• Vision : Subtle shifts of coloring, perceivable to the naked eye, are known as visual thresholds. If two colors are close enough in hue and value, they might not be discernible to the human eye. The minimally perceptible difference between these two similar colors is known as the difference threshold.
• Taste : In terms of taste, we can explore the smallest detectable change in sweetness or sourness. So, the minimum difference in the quantity of sugar in the cake a person can taste is known as the difference threshold. 
• Smell : The minutest difference in scent intensity is referred to as the smell threshold. The smallest detectable change in the amount of an aroma or fragrance is known as the difference threshold.
• Hearing : Similarly, when it comes to sound intensity or pitch, we can assess the minimum amount of change that one can sense between two similar sounds. So, the minimum change in the TV volume a person can perceive is known as the hearing difference threshold.
• Touch : The touch threshold is the slightest detectable variation in temperature. If, for example, a person feels a difference in temperature when touching two objects, the minimum perceivable change in heat between them is known as the touch threshold.
• Weight : The smallest variation in weight a person can detect between two objects is known as the “weight difference threshold.” In other words, if someone holds up two pens of differing weights and is asked to differentiate them, they may not be capable until there’s an ample difference.
• Pressure : Likewise, the pressure threshold is the minimum detectable difference in pressure between two stimuli. To put it another way, if a person tries to identify variations in pressure between two objects, they may not be able to detect any until the amount of pressure reaches an identifiable level.
• Luminance : The luminosity difference threshold is the minimum detectable change in brightness between two stimuli. For instance, minuscule fluctuations in light intensity are enough for humans to differentiate between two lighting sources.
• Size : The size difference threshold is the minimum size change between two objects that a person can detect. So, holding two boxes of different sizes in each hand, the person may not be able to tell the difference until one of them is much bigger than the other.
• Time : The temporal difference threshold is the minimum amount of time between two successive events that a person can perceive. For instance, if two events are presented in quick succession, the person may not be able to tell the difference until there is a considerable passage of time between them. 

Origins of Difference Threshold

Ernst Weber, a renowned physiologist, was the one who initially articulated the difference threshold concept. This theory was later further developed by another well-known psychologist Gustav Fechner.

Weber was the first one who highlights that two stimuli must be spaced a certain degree apart to be perceived. His research additionally discovered this minimal difference is typically a fraction of the average magnitude between them.

He introduced a law called the Weber law , which states that “the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus” (Wurm, 2022, p. 165).

Later, Fechner used Weber’s law to expand the concept of difference threshold further and proposed that any two similar stimuli can be distinguished by people only if they are different in intensity (Link, 2020). 

He termed this theory as the “just noticeable difference” (JND), which is widely employed in many disciplines to describe the difference between two stimuli.

While Weber highlights that a perceptible increase in sensation is proportionate to the present stimulus, Fechner’s law is inferred from Weber’s (with further assumptions), stating that our sense of intensity grows more gradually with a rise in energy — not at the same rate.

Absolute Threshold vs. Difference Threshold

The absolute threshold denotes the smallest possible level of stimulus that an individual can perceive through their senses , while a difference threshold refers to the smallest variance between two stimuli that someone can see or feel.

Absolute thresholds are usually associated with the individual’s ability to detect a single stimulus. It is the minimum intensity of any given stimulus that an individual can sense without background noise or other stimuli (Meligaard et al., 2007). 

On the other hand, difference thresholds are related to a person’s ability to identify the distinctions between two stimuli. It is the minimum amount of disparity between two similar stimuli that a person can single out and differentiate (Meligaard et al., 2007).

The absolute threshold serves as an indication of how much stimulus change the subject can detect and remember, whereas the difference threshold determines the smallest detectable amount of deviation in given stimuli.

The absolute threshold is usually measured in physical units, such as decibels or degrees Celsius.

The difference threshold, however, may differ based on the type of stimuli and can sometimes be measured in psychological units, such as identical points or just noticeable differences (JND).

How Difference Threshold is Calculated

The difference threshold is calculated by assessing the subject’s response to two similar stimuli, one of which has changed (Meligaard et al., 2007) . 

This is determined by the smallest level of change that the subject can perceive.

To measure the difference, two different stimuli must be tested. The reference stimulus is used as the foundation for comparison and remains constant.

Afterward, a slight alteration to the second stimulus is made before asking subjects if they can detect any changes.

When the subject is unable to differentiate between two levels of intensity, it indicates the difference threshold has been reached.

Importance of Difference Threshold

By exploring threshold differences and other related phenomena, scientists can gain insights into how humans perceive their environment and where misinterpretations may occur.

1. Understanding human perception

The difference threshold is crucial in understanding how humans perceive their environment.

By studying the difference threshold, researchers can better understand how different stimuli are perceived by an individual and how they could be incorporated into everyday communication and media.

2. Enhancing communication

A better understanding of the difference threshold can help improve communication between individuals and machines. Companies can use this knowledge to create more intuitive and interactive interfaces that provide users with a better experience.

3. Improving accuracy

By understanding the difference threshold, companies can create more accurate systems that measure data to a higher degree of accuracy. This could help them make better decisions when it comes to creating new products and services.

4. Enhancing marketing strategies

In many cases, companies use the difference threshold to create more effective marketing strategies.

By understanding what aspects of products people find most pleasing, they can focus their resources on improving those areas and boosting sales.

5. Developing better products

When designing new and better products, researchers often examine the just noticeable difference (JND).

For example, when phone manufacturers are crafting their devices, they are careful to measure and evaluate the JND of sound volume levels to ensure that people can clearly hear their music and calls.

A difference threshold is important in understanding how humans perceive and differentiate between stimuli. It measures the smallest possible change that an individual can detect.

This concept can be used to improve communication between individuals and machines, enhance accuracy in data collection, and create more targeted marketing strategies.

It is also important for developing better products that people will be able to use with ease. 

With a deeper understanding of difference thresholds, researchers can continue to develop new and exciting ways for people to interact with the world around them. 

Houston, J. P., Bee, H., & Rimm, D. C. (2013).  Invitation to psychology . Academic Press.

Link, S. W. (2020).  The wave theory of difference and similarity . Routledge.

Meilgaard, M., Civille, G. V., & Carr, B. T. (2007).  Sensory evaluation techniques . Taylor & Francis.

Wurm, S. (2022).  Consensus realities . ATICE LLC.

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Just Noticeable Difference (JND) in Psychology

How JND Affects Everyone

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Amy Morin, LCSW, is a psychotherapist and international bestselling author. Her books, including "13 Things Mentally Strong People Don't Do," have been translated into more than 40 languages. Her TEDx talk,  "The Secret of Becoming Mentally Strong," is one of the most viewed talks of all time.

Chris Stein / DigitalVision / Getty Images

Sometimes the difference between two things is glaring, like with a red car and a blue sedan. Other times it is barely noticeable, such as whether a toothbrush has 2,500 or 10,000 bristles. The amount of difference required for us to recognize that two items aren't the same is known as the just noticeable difference (JND).

Here we do a deeper dive into what the just noticeable difference is, why it's important, and how it was discovered. We also share how JND is measured, a few examples in everyday life, and how it is used to impact our buying decisions .

What is the Just Noticeable Difference?

The just noticeable difference, also known as the difference threshold, is the minimum level of stimulation that a person can detect 50% of the time. For example, if we were asked to hold two objects of different weights, the just noticeable difference would be the minimum weight difference between the two that we could sense half of the time.

Just noticeable difference is part of a field of study known as psychophysics. Psychophysics examines how physical stimuli in the environment affect and interact with mental processes. While scientists used to focus on measuring objective data, psychophysics allows them to measure subjective experiences as data.

The just noticeable difference applies to all five senses : touch, taste, smell, hearing, and sight. It can also apply to things such as brightness, sweetness, weight, pressure, and noisiness, among other factors.

Difference Threshold vs. Absolute Threshold

The just noticeable difference is not the same as the absolute threshold . While the difference threshold between two stimuli involves detecting differences in stimulation levels, the absolute threshold refers to the smallest detectable level of stimulation.

The absolute threshold for sound, for example, would be the lowest volume level that a person could detect. The just noticeable difference would be the smallest change in volume that a person could sense.

Importance of JND

Difference thresholds can help researchers understand how we respond to our environment . It also gives insight into where our senses are subject to error, such as in not being able to detect the differences between two things.

The just noticeable difference also impacts our preferences. For example, it can affect whether we prefer to drink skim, low-fat, or full-fat milk as each is slightly different in taste and visual appearance.

History of the JND Concept

The difference threshold was first described by Ernst Weber, a 19th-century physiologist and experimental psychologist , and later expanded upon by his student, psychologist Gustav Fechner. Weber's Law, also sometimes known as the Weber-Fechner Law, suggests that the just noticeable difference is proportionate to a variable's magnitude.

Weber studied the just noticeable difference using weights to see when subjects could detect when the weight was different. He discovered that we're better at detecting relative differences. In other words, when the weights got heavier, subjects needed a bigger difference between them to notice they were different.

How Just Noticeable Difference Is Measured

The JND is usually determined by conducting multiple trials and then using the smallest levels that participants could detect at least 50% of the time. To measure sensory information and difference thresholds, scientists rely on responses from study participants.

The measurements scientists take depend on the sensory information being received. For instance, when measuring heat, researchers may use joules. When measuring sound, they may use decibels instead.

Imagine that you present a sound to a subject and then slowly increase the decibel levels. You increase the sound level by 7 decibels before the participant notices that the volume is louder. In this case, the just noticeable difference is 7 decibels. Using this information, you can use Weber's law to predict the just noticeable difference for other sound levels.

Neural Activity

Our brains receive sensory input (such as light, sound, or taste), and our sensory organs convert this input into electrical signals. Therefore, measuring neural activity is another way in which researchers may determine how much (and what type of) sensory input a person is receiving.

Looking at a person's brain activation patterns seems to be a good way of measuring the just noticeable difference. For example, in one study, researchers found they could distinguish whether or not someone was touching something sticky based on their neural activity.

Stimulus Intensity

The intensity level of the stimulus can also play a role in how much people notice any changes. If a light is very dim, people may be more likely to notice smaller changes in intensity than they would if those same changes were made to brighter light.

For example, imagine being in a dark movie theater. When the house lights slowly start to turn on, this small change in the light intensity is immediately noticeable. However, upon leaving the theater and heading outside where the sun is shining brightly, these same changes in light intensity might be less noticeable since the stimulus level is much higher.

Does Just Noticeable Difference Change?

The just noticeable difference does change throughout the day. The amount and intensity of other stimuli experienced beforehand also affect how we perceive additional stimuli.

Examples of the Just Noticeable Difference 

The following are everyday examples in which the just noticeable difference can be observed.

Imagine that during a  psychology experiment , researchers ask all participants to hold two small amounts of sand in each hand. They slowly add tiny amounts of sand to one hand and ask when the subjects notice that one hand feels heavier than the other. The smallest weight difference that can be detected at least half the time is the just noticeable difference.

Another example of the just noticeable difference is watching television with someone else, but the volume is too low for us to hear. We ask them to turn it up and they press the volume button twice, but we still can't tell a difference. They then press the button two more times before we can notice an increase in volume.

Maybe we drink our coffee with sugar in it . When staying at a friend's house, our friend makes the coffee for us but we don't taste the sweetness. They likely didn't add enough sugar for us to meet our threshold and, thereby, notice the difference.

We dye our hair but afterward, the color still looks the same as it did before. This may be because we dyed it a similar shade to what we already had, and the color isn't above the difference threshold.

Uses for the Just Noticeable Difference

The JND is often studied in product development. For instance, when manufacturing cell phones, companies measure the JND of sound so there are noticeable increases when the volume is raised on the device. Companies that create food products can also study the JND to understand consumer preferences.

Companies may take advantage of the JND in several ways. For instance, a company may determine the JND of a price point. This enables it to increase the price of a product so slightly that consumers likely won't notice it.

Companies can also use the just noticeable difference to reduce the size of their packages, such as boxes of pasta or cans of corn. They'll knowingly decrease the size by an amount that is below the difference threshold, so people don't realize that their favorite products have gotten smaller.

Downsizing packaging saves companies money, but it's often seen as an unethical practice—"tricking" the consumer into buying their favorite products at the same (or higher) prices, so they're getting less without knowing it.

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Kim J, Yeon J, Ryu J, et al. Neural activity patterns in the human brain reflect tactile stickiness perception .  Front Hum Neurosci . 2017;11:445. doi:10.3389/fnhum.2017.00445

Çakır M, Balagtas JV. Consumer response to package downsizing: Evidence from the Chicago ice cream market . J Retail. 2014;90(1):1-12. doi:10.1016/j.jretai.2013.06.002

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Basics: neuroscience and psychophysics

2 Psychophysical Methods

Learning Objectives

Be able to diagnose whether a given experiment measures an absolute threshold, a difference threshold, or is a magnitude estimation experiment

Be able to describe a couple of different methods of estimating a threshold

Know what a subliminal message is

Know Weber’s law (also called Weber-Fechner law)

The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold. Absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. Another way to think about this is by asking how dim can a light be or how soft can a sound be to still be detected half of the time. The sensitivity of our sensory receptors can be quite amazing. It has been estimated that on a clear night, the most sensitive sensory cells in the back of the eye can detect a candle flame 30 miles away (Okawa & Sampath, 2007). Under quiet conditions, the hair cells (the receptor cells of the inner ear) can detect the tick of a clock 20 feet away (Galanter, 1962).

It is also possible for us to get messages that are presented below the threshold for conscious awareness—these are called subliminal messages. A stimulus reaches a physiological threshold when it is strong enough to excite sensory receptors and send nerve impulses to the brain: This is an absolute threshold. A message below that threshold is said to be subliminal—we receive it, but we are not consciously aware of it. Over the years there has been a great deal of speculation about the use of subliminal messages in advertising, rock music, and self-help audio programs. Research evidence shows that in laboratory settings, people can process and respond to information outside of awareness. But this does not mean that we obey these messages like zombies; in fact, hidden messages have little effect on behavior outside the laboratory (Kunst-Wilson & Zajonc, 1980; Rensink, 2004; Nelson, 2008; Radel, Sarrazin, Legrain, & Gobancé, 2009; Loersch, Durso, & Petty, 2013).

Subliminal messages exert diverse influences on our thoughts and our behavior ( van Gaal et al., 2012 ; Hassin, 2013 ). Subliminal stimuli can facilitate conscious processing of related information ( Van den Bussche et al., 2009 ), change our current mood ( Monahan et al., 2000 ), boost our motivation ( Aarts et al., 2008 ), and can even alter our political attitudes and voting intentions ( Hassin et al., 2007 ; Weinberger and Westen, 2008 ). With such a broad impact, subliminally planted information might have the potential to alter our decisions in everyday situations such as voting.

In order to influence decision-making in real-life situations, subliminal messages must be stored for long-term after only a few exposures, e.g. after a single confrontation with a subliminal TV advert. Furthermore, messages must be stored even if they contain complex relational information that requires semantic integration, such as “politician X will lower the taxes.” For subliminal manipulation to be effective, humans thus have to be able to semantically integrate and rapidly store unconscious pieces of novel information into long-lasting associative memories that can be retrieved if relevant to the context of a later decision.

Methods for estimating thresholds

When we design experiments, we have to decide how we’re going to approach a threshold estimation. Here are three common techniques

• Method of Limits . The experimenter can increase the stimulus intensity (or intensity difference) until the observer detects the stimulus (or the change). For example, turn up the volume until the observer first detects the sound. This is intuitive, but it is subject to bias — the estimated threshold is likely to be different, for example, if we start high and work down vs. start low and work up.
• Method of Adjustment. This is very much like the Method of Limits, except the experimenter gives the observer the knob: “adjust the stimulus until it’s very visible” or “adjust the color of the patch until it matches the test patch.”
• Method of Constant Stimuli . This is the most reliable, but most time-consuming. You decide ahead of time what levels you are going to measure, do each one a fixed number of times, and record % correct (or the number of detections) for each level. If you randomize the order, you can get rid of bias.

Absolute thresholds are generally measured under incredibly controlled conditions in situations that are optimal for sensitivity. Sometimes, we are more interested in how much difference in stimuli is required to detect a difference between them. This is known as the just noticeable difference (JND) or difference threshold. Unlike the absolute threshold, the difference threshold changes depending on the stimulus intensity. As an example, imagine yourself in a very dark movie theater. If an audience member were to receive a text message on her cell phone which caused her screen to light up, chances are that many people would notice the change in illumination in the theater. However, if the same thing happened in a brightly lit arena during a basketball game, very few people would notice. The cell phone brightness does not change, but its ability to be detected as a change in illumination varies dramatically between the two contexts. Ernst Weber proposed this theory of change in difference threshold in the 1830s, and it has become known as Weber’s law: the difference threshold is a constant fraction of the original stimulus, as the example illustrates.

Weber’s law is approximately true for many of our senses—for brightness perception, visual contrast perception, loudness perception, and visual distance estimation, our sensitivity to change decreases as the stimulus gets bigger or stronger. However, there are many senses for which the opposite is true: our sensitivity increases as the stimulus increases. With electric shock, for example, a small increase in the size of the shock is much more noticeable when the shock is large than when it is small. A psychophysical researcher named Stanley Smith Stevens asked people to estimate the magnitude of their sensations for many different kinds of stimuli at different intensities, and then tried to fit lines through the data to predict people’s sensory experiences (Stevens, 1967). What he discovered was that most senses could be described by a power law of the form P ∝S n where P is the perceived magnitude, ∝ means “is proportional to”, S is the physical stimulus magnitude, and n is a positive number. If n is greater than 1, then the slope (rate of change of perception) is getting larger as the stimulus gets larger, and sensitivity increases as stimulus intensity increases. A function like this is described as being expansive or supra-linear. If n is less than 1, then the slope decreases as the stimulus gets larger (the function “rolls over”). These sensations are described as being compressive. Weber’s Law is only (approximately) true for compressive (sublinear) functions; Stevens’ Power Law is useful for describing a wider range of senses.

Both Stevens’ Power Law and Weber’s Law are only approximately true. They are useful for describing, in broad strokes, how our perception of a stimulus depends on its intensity or size. They are rarely accurate for describing perception of stimuli that are near the absolute detection threshold. Still, they are useful for describing how people are going to react to normal everyday stimuli.

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OpenStax, Psychology Chapter 5.1 Sensation and Perception. Provided by: Rice University. Download for free at https://cnx.org/contents/[email protected]:K-DZ-03P@12/5-1-Sensation-versus-Perception. License: Creative Commons Attribution 4.0

Galanter, E. (1962). Contemporary Psychophysics. In R. Brown, E.Galanter, E. H. Hess, & G. Mandler (Eds.), New directions in psychology. New York, NY: Holt, Rinehart & Winston.

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Okawa, H., & Sampath, A. P. (2007). Optimization of single-photon response transmission at the rod-to-rod bipolar synapse. Physiology, 22, 279–286.

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Stevens, S. S. (1957). On the psychophysical law. Psychological Review 64(3):153—181. PMID 13441853

Introduction to Sensation and Perception Copyright © 2022 by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Difference Threshold in Psychology: Understanding Just Noticeable Differences

A single grain of rice on a plate might seem insignificant, but when it comes to our sensory perception, the smallest detectable change can make a world of difference. This concept, known as the difference threshold in psychology, plays a crucial role in how we perceive and interact with the world around us. It’s the foundation upon which our senses operate, allowing us to detect changes in our environment and respond accordingly.

Imagine you’re at a concert, and the music suddenly gets a tad louder. Did you notice? Or perhaps you’re trying on a new pair of shoes, and they feel just a smidge tighter than your old ones. These subtle changes in our sensory experiences are what psychologists refer to as the difference threshold. It’s the minimum amount of change in a stimulus that we can detect.

Diving into the World of Difference Thresholds

The difference threshold is a fascinating concept that lies at the heart of sensory perception. It’s not just about detecting changes; it’s about understanding how our brains process and interpret these changes. This threshold varies from person to person and can be influenced by a variety of factors, including age, attention, and even our emotional state.

But why is this concept so important? Well, it helps us understand how we interact with our environment and make decisions based on sensory input. From choosing the perfect wine to adjusting the volume on our headphones, the difference threshold plays a role in countless aspects of our daily lives.

As we delve deeper into this topic, we’ll explore related concepts such as Just Noticeable Difference in Psychology: Exploring Sensory Thresholds , which is closely tied to the difference threshold. We’ll also look at how these concepts apply to various sensory modalities and their practical implications in fields ranging from product design to clinical psychology.

The Just Noticeable Difference: A Key Player in Sensory Perception

The Just Noticeable Difference (JND) is a term you’ll often hear in discussions about difference thresholds. But what exactly is it? Simply put, the JND is the smallest change in a stimulus that can be reliably detected. It’s like the minimum update your senses need to register a difference.

The concept of JND has a rich history in psychology, dating back to the 19th century. It was first introduced by German physiologist Ernst Heinrich Weber and later refined by Gustav Fechner, who is considered one of the founders of psychophysics. These early pioneers laid the groundwork for our understanding of how we perceive and discriminate between different stimuli.

The relationship between JND and difference threshold is like that of two peas in a pod. While the difference threshold refers to the minimum amount of change needed for detection, the JND quantifies this change. It’s the measurable manifestation of the difference threshold.

Let’s consider some everyday examples to bring this concept to life. Have you ever tried to adjust the brightness on your phone screen, only to find that you can’t see a difference between two adjacent settings? That’s because the change is below your JND for brightness. Or think about trying to distinguish between two very similar shades of blue in a paint store. The point at which you can reliably tell them apart is your JND for color discrimination.

Weber’s Law: The Mathematical Backbone of Difference Thresholds

Now, let’s talk about a fundamental principle in psychophysics: Weber’s Law. Named after Ernst Heinrich Weber, this law provides a mathematical framework for understanding difference thresholds. It states that the just noticeable difference between two stimuli is proportional to the magnitude of the stimuli.

In simpler terms, Weber’s Law suggests that the size of the difference we can detect depends on the intensity of the original stimulus. For example, if you’re in a quiet room, you might notice even a slight whisper. But in a noisy restaurant, you’d need a much louder sound to notice a difference.

The Weber’s Law in Psychology: Understanding Sensory Perception and Discrimination is often expressed as ΔI / I = k, where ΔI is the just noticeable difference, I is the initial stimulus intensity, and k is a constant known as the Weber fraction. This fraction varies for different sensory modalities but remains relatively constant within each modality.

Let’s apply this to real-life scenarios. Consider lifting weights. You might easily notice the difference between a 5-pound weight and a 6-pound weight. But the difference between a 50-pound weight and a 51-pound weight? Not so much. According to Weber’s Law, you’d need to add about 5 pounds to the 50-pound weight to notice a difference – the same 10% increase that allowed you to distinguish between 5 and 6 pounds.

This principle applies across various sensory modalities. In vision, for instance, it explains why we can easily detect a single candle being lit in a dark room, but might not notice an additional streetlight on a brightly lit street. In audition, it helps explain why we need to turn up the volume more at higher volume levels to perceive an increase in loudness.

Exploring Difference Thresholds Across Sensory Modalities

Our senses are the windows through which we experience the world, and each has its own unique difference threshold. Let’s take a sensory journey to explore how difference thresholds manifest in various modalities.

Starting with vision, consider the subtle gradations in a sunset. The point at which you can distinguish one shade of orange from another is your visual difference threshold for color. Similarly, when you’re trying to read increasingly smaller text on an eye chart, the smallest size you can reliably read represents your difference threshold for visual acuity.

Moving to audition, imagine you’re at a symphony. The conductor gradually increases the volume of the orchestra. The moment you notice this change represents your auditory difference threshold for loudness. Or think about tuning a guitar – the smallest pitch difference you can detect is your difference threshold for frequency.

Touch, or tactile sensation, also has its thresholds. Run your fingers over different grades of sandpaper. The point at which you can feel a difference in texture is your tactile difference threshold. Temperature sensitivity is another aspect of touch – the smallest change in temperature you can feel on your skin represents this threshold.

Don’t forget about smell and taste! The difference threshold in olfaction might be represented by your ability to detect a slight increase in the intensity of a perfume. In gustation, it could be your ability to notice a small addition of salt to your soup.

These examples highlight how Stimulus Discrimination in Psychology: Understanding Its Role in Learning and Behavior is intimately tied to difference thresholds across all our senses.

The Science of Measuring Difference Thresholds

Measuring difference thresholds is a delicate science that requires precise methods and careful analysis. Psychologists and researchers use various techniques to determine these thresholds, each with its own strengths and challenges.

One common method is the method of constant stimuli. In this approach, participants are presented with a standard stimulus and a comparison stimulus that varies in intensity. They’re asked to judge whether the comparison is greater or less than the standard. By analyzing the responses across many trials, researchers can determine the point at which differences become noticeable.

Another technique is the staircase method. Here, the intensity of the comparison stimulus is adjusted based on the participant’s responses. If they notice a difference, the next comparison is made more similar to the standard. If they don’t notice a difference, it’s made more different. This process continues until a reliable threshold is determined.

Calculating the difference threshold often involves using Weber’s fraction. Remember the formula ΔI / I = k? By determining the value of k for a particular sensory modality, researchers can predict the just noticeable difference for various stimulus intensities.

However, measuring difference thresholds isn’t without its challenges. Factors like attention, fatigue, and individual differences can all affect the results. Moreover, some sensory experiences are more subjective than others, making precise measurements difficult.

It’s also worth noting that difference thresholds aren’t fixed values. They can change based on various factors, including age, experience, and even the presence of certain medical conditions. This variability adds another layer of complexity to the study of difference thresholds.

From Lab to Life: Applications of Difference Threshold Research

The study of difference thresholds isn’t just an academic exercise – it has real-world applications that touch many aspects of our lives. From product design to clinical assessments, understanding difference thresholds can lead to significant improvements in various fields.

In product design, knowledge of difference thresholds helps create more effective and user-friendly products. For example, understanding visual difference thresholds is crucial in designing displays for electronic devices. How much should the brightness increase with each step on the slider? That’s a question of difference thresholds.

The food and beverage industry also benefits from this research. When developing new flavors or adjusting existing recipes, knowing the gustatory difference thresholds helps determine how much a flavor needs to change for consumers to notice and appreciate the difference.

In clinical psychology and neurology, difference threshold tests can be valuable diagnostic tools. Changes in sensory thresholds can sometimes indicate neurological conditions or the progression of certain diseases. For instance, altered difference thresholds in touch sensation might be an early sign of neuropathy in diabetic patients.

The field of human-computer interaction heavily relies on understanding difference thresholds. When designing interfaces, knowing how small a change users can detect helps in creating more intuitive and responsive systems. This knowledge informs decisions about everything from the size of icons to the sensitivity of touch screens.

As we look to the future, research on difference thresholds continues to evolve. New technologies are allowing for more precise measurements and opening up new areas of study. For example, virtual reality environments offer exciting possibilities for studying difference thresholds in complex, controlled settings.

Moreover, as we delve deeper into the realms of artificial intelligence and machine learning, understanding human sensory thresholds becomes crucial. How can we create AI systems that perceive the world in ways that align with human perception? The answer lies, in part, in our understanding of difference thresholds.

Wrapping Up: The Big Picture of Small Differences

As we’ve journeyed through the world of difference thresholds, we’ve seen how this seemingly simple concept – the smallest detectable change in a stimulus – has far-reaching implications. From the foundational ideas of just noticeable differences and Weber’s Law to the varied applications in product design and clinical assessments, difference thresholds are a crucial part of how we understand and interact with our world.

Remember that single grain of rice we started with? It’s a perfect metaphor for the difference threshold. Just as that grain might be the tipping point that makes a difference in a culinary creation, the smallest perceptible change can make a significant difference in how we experience and respond to our environment.

Understanding difference thresholds isn’t just about perception – it’s about Threshold Psychology: Exploring the Tipping Points of Human Behavior and Decision-Making . It helps us grasp how we make decisions based on sensory input, how we distinguish between similar stimuli, and even how we might improve our sensory acuity.

As we continue to explore the intricate workings of the human mind, concepts like difference thresholds serve as valuable tools. They bridge the gap between our subjective experiences and objective measurements, helping us quantify and understand the nuances of perception.

So, the next time you notice a subtle change in your environment – be it a slight shift in lighting, a faint new aroma, or a barely perceptible change in texture – take a moment to appreciate the remarkable sensitivity of your senses. You’re experiencing your own personal difference thresholds in action, a testament to the incredible complexity and capability of the human perceptual system.

In the grand symphony of sensory experiences that make up our daily lives, it’s often the smallest notes – those just at the edge of our perception – that add the most intriguing harmonies. By understanding and appreciating these subtle nuances, we gain a richer, more nuanced appreciation of the world around us.

References:

1. Goldstein, E. B. (2014). Sensation and Perception. Cengage Learning.

2. Gescheider, G. A. (2013). Psychophysics: The Fundamentals. Psychology Press.

3. Kandel, E. R., Schwartz, J. H., & Jessell, T. M. (2000). Principles of Neural Science. McGraw-Hill.

4. Weber, E. H. (1834). De Pulsu, Resorptione, Auditu et Tactu: Annotationes Anatomicae et Physiologicae. C.F. Koehler. https://archive.org/details/depulsuresorpti00webe

5. Fechner, G. T. (1860). Elemente der Psychophysik. Breitkopf und Härtel.

6. Stevens, S. S. (1957). On the psychophysical law. Psychological Review, 64(3), 153–181. https://doi.org/10.1037/h0046162

7. Kingdom, F. A. A., & Prins, N. (2016). Psychophysics: A Practical Introduction. Academic Press.

8. Laming, D. (2013). The Measurement of Sensation. Oxford University Press.

9. Ehrenstein, W. H., & Ehrenstein, A. (1999). Psychophysical methods. In U. Windhorst & H. Johansson (Eds.), Modern Techniques in Neuroscience Research (pp. 1211-1241). Springer.

10. Gescheider, G. A., Bolanowski, S. J., & Verrillo, R. T. (2004). Some characteristics of tactile channels. Behavioural Brain Research, 148(1-2), 35-40. https://doi.org/10.1016/S0166-4328(03)00177-3

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Chapter 78 . Absolute Thresholds and Difference Thresholds

Learning objectives.

Describe the role of the absolute threshold in detecting a stimulus.

Contrast the absolute threshold with the difference threshold.

Explain how Weber’s Law predicts the size of the just noticeable difference (JND).

Select the NEXT button to continue with the Review.

1. The first step in perception —understanding what is happening in the world around us—is to become aware that some form of stimulus energy is striking our sensory receptors . This detection process is called sensation .

2. How much stimulus energy is necessary before we can sense that something is happening in our environment? The minimum amount of stimulus energy that is detectable on average is called the absolute threshold . A threshold is a “cross-over” point, such as a doorway separating one room from another. When a mosquito is flying a few feet away, the buzzing sound may be too soft to hear. But, as the mosquito gets close to our ear, the sound energy crosses our absolute threshold, and we become aware of the buzz.

3. How is the absolute threshold measured? If we flash a light briefly 100 times, randomly varying the brightness of the light on each trial, the results will look like the blue curve on this graph. As the stimulus energy increases, the likelihood that a person will detect the stimulus increases. The absolute threshold, shown as a red dot, is the amount of light energy that is needed in order for this particular person to have a 50 percent chance of seeing the light.

4. Because there is random activity (“background noise”) within each sensory system , sometimes a light that is slightly above the absolute threshold will not be detected. Likewise, sometimes the person will detect a light that is slightly below the absolute threshold.

5. Once a stimulus is above our absolute threshold , how much additional energy is needed in order for us to detect that the stimulus has changed? This is called the difference threshold , and the minimum amount of energy change is called the just noticeable difference (JND) . Imagine that you are turning up the volume on a sound system. How much would the physical intensity of the sound need to increase before you could hear that the sound had become louder ?

6. Weber’s law tells us that the just noticeable difference (JND) is not a constant amount of stimulus energy, but instead is a constant percentage of the current stimulus energy. If the JND for loudness of a sound is 5 percent (or 1/20), increasing the sound system’s volume setting from 20 units to 21 units should, on average, be just enough to produce a noticeably louder sound. But if the setting is already at 40 units, we would need to add 2 units in order to hear the difference in loudness.

Practice 1: Testing the Absolute Threshold

On each trial, drag the slider to one of the 10 different levels of stimulus energy, and select the PLAY SOUND button. The participant will make a response, and we’ll plot the results. There will only be 10 trials, but each trial will simulate 4 additional trials at the same intensity level.

We are going to simulate an experiment on testing the absolute threshold for this participant. You will control the intensity of a sound stimulus , and this participant will indicate whether he can detect a sound at each level of intensity. When you have tested all 10 levels of stimulus energy (and viewed the completed response curve), we will calculate the absolute threshold for this individual.

The absolute threshold for this participant seems to be about 40 units of sound intensity. On average, if the stimulus had at least that much intensity, he could detect it. Now, select the NEXT button and move to Practice 2.

Practice 2: Testing the Difference Threshold

On each trial, drag the slider to one of the 8 different levels of stimulus energy, and select the PLAY SOUND button. The participant will hear two sounds, and will indicate whether the sounds have the same or different loudness. Then, we’ll plot the results. There will only be 8 trials, but each trial will simulate 4 additional trials at the same intensity level.

Now we will simulate an experiment on testing the difference threshold for this participant. We will begin each trial by playing a “standard” sound of 60 units of sound intensity, which is well above this participant’s absolute threshold. This will be followed by a second “comparison” sound of varying intensity (ranging from 61 to 68 units), which you will control. The participant will indicate whether he can detect a difference in the loudness of the sound at each level of intensity. When you have tested all 8 levels of stimulus energy (and viewed the completed response curve), we will calculate the difference threshold for this individual.

The difference threshold—or just noticeable difference (JND)—for this participant seems to be about 3 units of sound intensity. On average, if the stimulus had changed by at least that much intensity from the original intensity of 60 units, he could detect the change in loudness. The ratio of the JND to the original intensity was 3/60 or 1/20 (5 percent). Now, select the NEXT button and move to Practice 3.

Practice 3: Applying Weber’s Law

Select each of the buttons to see what happens.

Now, let’s put Weber’s law into action. This research participant is in a completely dark room, illuminated only by some candles burning on a table behind her. If we added a new candle, would she notice that the room had become brighter? Weber’s Law states that the just noticeable difference (JND) is a constant ratio of the original stimulus energy. From earlier research, we know that the “Weber ratio” for detecting a change in the brightness of a light is about 1/12, or 8 percent. Let’s test this by varying the number of original candles, and then adding one new candle.

The change in stimulus intensity is 1/4, or 25 percent. Because this change is greater than the JND of 8 percent, this participant easily detected the difference in brightness.

The change in stimulus intensity is 1/20, or 5 percent. Because this change is smaller than the JND of 8 percent, this participant could not detect the difference in brightness.

Match the terms with their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

For each statement, select one of the buttons to indicate whether the statement is True or False . When a response has been placed for all statements, select the CHECK ANSWER button.

Just Noticeable Difference In Psychology: Examples

Just noticeable difference was investigated by a 19th century psychologist called Gustav Fechner, who perfected the technique.

Just noticeable difference in psychology is the amount a sensation, like weight, has to be changed in order to be noticeable.

For example, imagine you have an orange in each hand, but one is slightly heavier than the other.

How small does the difference in weight between the oranges have to be before you can notice?

That is just noticeable difference.

Just noticeable difference is a part of an area of psychology called psychophysics, which is the scientific study of how our sensations and perceptions are affected by stimuli.

Development of just noticeable difference

Just noticeable difference or the difference threshold was first described by the physiologist Ernst Weber.

It was expanded on by Gustav Fechner, a physicist turned proto-psychologist.

It was Fechner who, with the publication of his masterwork Elements of Psychophysics in 1860, is often credited with helping to found experimental psychology ( Fechner, 1860 ).

Strange, really, for a man who set out to prove plants have souls.

Psychophysics might have a name that sounds exciting, but its experimental methods are pretty dull.

Just noticeable difference examples

What Fechner was interested in was measurement, measuring the relationship between a stimulus and the resulting sensation.

He did this using a variety of experimental methods.

Typically, though, he would give a participant two weights and ask them which they thought was heavier.

Then he would repeat this procedure over and over and over again until he was satisfied he had enough measurements.

In one such experiment he took 24,576 measurements.

Fechner wanted to prove there was a mathematical relationship between stimulus and sensation.

In doing this he perfected the technique of measuring ‘just noticeable difference’ gained from his mentor, Ernst Weber.

This is done by decreasing the differences between different stimuli – say the weight of two balls – until the participant can no longer tell them apart.

It is not just weights that were investigated.

Psychologists have looked at the smallest changes in levels of light that people can detect, the smallest levels of pressure, sound, smell, hearing, touch and taste — the list goes on.

The soul-life of plants

The irony is that Fechner set about this huge mountain of rather hard-headed measurements for quite whimsical reasons.

He wanted to provide evidence for his philosophical ideas, most notable amongst these was his insistence that plants had minds.

Indeed he devoted a whole book to discussing the ‘soul-life of plants’.

Fechner also believed that plants, like humans were part of a hierarchy of minds, at the top of which sat our sun, and above that, the universe as a whole.

These free-floating ideas seem a far cry from the 24,576 meticulous measurements, but such is the human spirit.

Few of Fechner’s ideas have survived in modern psychophysics and yet Fechner’s obsession with measurement lives on today in many areas of psychology.

Indeed, it is for his methods more than his findings that he is celebrated.

It has been argued that ability measurement is the single largest contribution psychology has made to society ( Michell, 1999 ).

While IQ and personality test may not bear much direct relation to Fechner’s ideas, their spirit is the same: to measure, to quantify, to know the difference between.

Author: Dr Jeremy Dean

Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology. He has been writing about scientific research on PsyBlog since 2004. View all posts by Dr Jeremy Dean

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JUST NOTICEABLE DIFFERENCE (JND; Differential or Difference Threshold)

The smallest difference between two stimuli that can be reliably detected.The external world comes to us in the form of ever-changing sensations, and we are constantly called upon to react to slight differences in sounds, colors, shapes and sizes. We could not enjoy a great painting, drive a car safely, play a good game of tennis, or do any precision work if we were not able to make fine discriminations. It is important, therefore, to find out just how sensitive we are to differences— that is, what is the least difference in length, or loudness, or brightness that we can detect?This was probably the first question ever to be answered experimentally in the history of psychology. Early in the nineteenth century the German physicist, Ernst Weber, developed a technique for measuring the JND, or differential threshold, for different senses. In determining the IND for weight, for example, he would ask a subject to heft an unmarked weight of, say, 300 grams repeatedly, and then heft other weights until he found one that was just noticeably heavier than the given weight on 75 per cent of the trials. The result was then stated in fractional form: if the new weight was 306 grams, the “ Weber fraction ,” as it was later called, would be %()0, or %0. The experiment was continued with other weights, and he found that if the base weight was 600, the JND weight was 612; and if the base weight was 200, the JND weight was 204. When he determined the fraction in each case, he made the startling discovery that it was exactly the same in every instance—that is,Weber performed tests on different senses and made the even more astonishing discovery that there was a constant fraction for each of them. He found, for instance, that if he started with 60 lighted candles, it took one additional candle to make a noticeable difference. If he started with 120 candles; it took two, and so on. Here the fraction was %0 in every case. This finding led to Weber’s Law, first proposed in 1834: the smallest noticeable difference in perceived intensity is a constant fraction of the original stimulus.Weber’s Law has been found to hold, with some variation, for all senses— but only in the middle range of intensity. This limitation does not greatly diminish its value, since most of our experiences involve stimuli of medium intensity. The most important Weber fractions (or Weber constants) are: vision (for brightness of white light ): %0; for kinesthesis (lifted weights): y50; for pain (heat on skin): %0; for hearing (middle pitch, moderate loudness): for pressure (on skin spots): y7; for smell (odor of India rubber): %; for taste (table salt): %. Many other fractions have been determined—for example, for visual detection of differences in length (%0o)—but fractions for each modality always remain about the same.These results shed interesting light on our sense experience . They indicate that vision is our most sensitive, and smell and taste our least sensitive modality. Moreover, these sensitivities seem to be roughly proportionate to the importance of the different sense organs, since we depend far more on vision than on taste or smell for survival. The only result that is surprising is our extremely high kinesthetic sensitivity . We use our muscle sense in learning the proper “reaches” on the typewriter or piano, and in acrobatics or dancing, but we seldom use this sense to its fullest advantage.Animal studies lend support to the evolutionary hypothesis. Weber fractions obtained from discrimination experiments show that fish are extremely sensitive to tastes, dogs and cats to smell, and bats to high-pitched sounds. Each of these senses is of high survival value for the particular animal.The Weber fractions given above are, of course, only averages, for there are wide individual differences in sensitivity. They would be far smaller for tea and wine tasters or perfume specialists than for the average person. Such individuals can detect, within an incredibly small margin of error whether a batch of a certain product meets a certain standard. Sensitivity of this kind is undoubtedly increased through training, but it may also be due in part to constitutional factors. At any rate it has considerable survival value of the economic kind, since these experts are usually in great demand.Weber’s Law has been applied in a variety of fields, including esthetics, consumer attitudes, and stock-market analysis. Artists can usually perceive differences in color values, shape and size that are imperceptible to the untrained eye, and the layman may actually perceive differences without being fully aware of them. Experiments show that if extremely slight changes are made in a work of art they are likely to make a noticeable difference in our reaction. (An equivalent change in a publicity poster would be completely overlooked.) In practical matters, a five- cent increase in the price of a newspaper will cause a violent reaction, while a one hundred or two hundred dollar increase in the price of a $40,000 house would cause little concern.Sometimes, however, a series of changes which are close to the differential threshold will go unnoticed until they produce a major shift—for example, fractional increases in the cost of living index may “sneak up” on us until we suddenly have an inflation on our hands. The same idea lies behind warnings against “creeping socialism.” It also applies to progressive disorders, such as deafness, schizophrenia and brain tumor , which grow worse at an extremely slow rate. In terms of the JND, each change is so small that it does not reach the threshold of perceptibility, and therefore the condition often goes undetected until it has reached an advanced state. The term “insidious onset” is used to describe this process.

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Difference Threshold: Psychology Definition, History & Examples

In the realm of psychophysics , the concept of the difference threshold stands as a pivotal term. It refers to the minimum noticeable difference that a person can perceive between two stimuli.

Psychologist Gustav Fechner is credited with formalizing this concept in the 19th century, which is sometimes termed the ‘just noticeable difference’ (JND). Fechner’s work laid the groundwork for subsequent explorations into sensory processing and perception .

Examples of the difference threshold are commonly encountered in everyday life, such as discerning the change in brightness of a light or the alteration in volume of a sound.

This introduction will delve into the nuanced definition of the difference threshold, trace its historical development, and illuminate its application through real-world instances, while also discussing related terms and providing references for further inquiry.

Table of Contents

The difference threshold, also known as the just noticeable difference (JND), is the smallest change in stimulus intensity needed for us to notice a difference in our sensory experience. It helps us understand how sensitive our senses are to detecting changes in the environment .

This threshold varies among individuals and is influenced by factors like the type of sense and the surrounding context. It has implications for fields like neuroscience and marketing.

The term ‘just-noticeable difference’ has its historical origins in the field of psychology and can be traced back to the pioneering work of Ernst Heinrich Weber, a German psychologist of the 19th century. Weber’s research laid the foundation for understanding sensory perception and led to the development of what is now known as Weber’s Law .

Weber’s Law, established by Ernst Weber, is an empirical law that quantifies the perception of change in a given stimulus. It states that the ratio of the increment threshold to the background intensity remains constant. In simpler terms, this law explains how humans perceive differences in stimuli, such as the ability to detect changes in the intensity of a sound or the brightness of a light.

Weber’s Law was a significant breakthrough in the study of psychophysics, which explores the relationship between physical stimuli and the resulting sensory experiences. By establishing a systematic connection between measurable physical stimuli and the perceived differences in sensory experience, Weber’s work became fundamental to the field of psychology.

Weber’s contributions to psychology laid the groundwork for further exploration in the realm of sensory perception. His research inspired subsequent studies and investigations, contributing to the evolution of the concept of just-noticeable difference. The principle of the just-noticeable difference continues to be a crucial aspect of understanding human perception and forms the basis for various psychological theories and experiments in modern times.

While Weber’s Law may sound complex, it can be easily understood through relatable examples from everyday life. Let’s consider a few scenarios:

• Adjusting the volume on a music player: Have you ever noticed that when you increase the volume from a low level, you can easily hear the difference? However, as the volume gets louder, you need to make a larger change for it to be noticeable. This is because of Weber’s Law in action. The law states that the just-noticeable difference in loudness is proportional to the initial volume level. So, the higher the volume, the larger the change needed to perceive a difference.
• Dimming the lights in a bright room: Imagine you’re in a well-lit room and someone slowly dims the lights. At first, you might not notice the change, but once the lights pass a certain threshold, you suddenly become aware of the dimming. This threshold is determined by Weber’s Law, which states that the just-noticeable difference in brightness depends on the initial level of luminosity. In other words, the more light there is initially, the bigger the change needed for it to be noticeable.

These real-life examples demonstrate how Weber’s Law can be applied to our everyday experiences. It helps us understand that our perception of differences in various sensory modalities, such as sound and light, is not linear but rather depends on the intensity of the initial stimulus.

Related Terms

Understanding the difference threshold’s role in sensory perception warrants an exploration of related psychological terms such as ‘absolute threshold’ and ‘sensory adaptation.’ These terms are closely linked to the difference threshold and provide valuable insights into the perceptual processes.

The absolute threshold refers to the minimum intensity of a stimulus required to be consciously detected 50% of the time. It serves as a benchmark for the sensory system’s capabilities to register sensation before a comparative evaluation, like that of the difference threshold, comes into play. While the difference threshold focuses on the ability to detect changes in stimuli, the absolute threshold focuses on the ability to detect the presence of a stimulus.

Sensory adaptation, on the other hand, describes the diminished sensitivity to a constant stimulus over time. This neurological phenomenon allows organisms to economize on attentional resources by filtering out nonessential stimuli. Unlike the difference threshold, which involves detecting changes in stimuli, sensory adaptation involves the adjustment of sensory receptors to maintain sensitivity in response to a constant stimulus.

Both concepts are integral to understanding perceptual processes and their thresholds, with the difference threshold focusing on detecting changes and sensory adaptation focusing on adapting to constant stimuli.

The following reputable sources, studies, and publications have contributed to a better understanding of the difference threshold in psychology.

Classic works by Gustav Fechner and his predecessors, such as Ernst Weber, have laid the foundation for our understanding of sensory discrimination and the difference threshold. Fechner’s book ‘Elements of Psychophysics’ (1860) and Weber’s research on just noticeable differences (1834) are seminal works in this area.

Modern texts, like ‘Sensation and Perception’ by Jeremy M. Wolfe et al. (2012), have expanded upon these principles and explored their application in contemporary psychological studies. This comprehensive textbook covers various topics related to sensation and perception, including the difference threshold.

Scholarly articles also play a crucial role in advancing our understanding of the difference threshold. For example, studies like ‘The Role of Attention in Perceptual Sensitivity: Evidence from Psychophysical Studies and Event-Related Potentials’ by Steven J. Luck and Andrew Hollingworth (2009) provide empirical evidence to support theoretical frameworks surrounding the difference threshold. These articles often employ rigorous methodologies, ensuring that their conclusions are grounded in systematic observation or experimentation .

When engaging with these references, it is important to critically evaluate the validity and reliability of the findings presented. Considering the context of the research and its contribution to the broader psychological discourse is essential for further reading and understanding of the difference threshold.

References:

• Fechner, G. T. (1860). Elements of psychophysics. Leipzig, Germany: Breitkopf & Härtel.
• Weber, E. H. (1834). De pulsu, resorptione, auditu et tactu: Annotationes anatomicae et physiologicae. Leipzig, Germany: Cnobloch.
• Wolfe, J. M., Kluender, K. R., Levi, D. M., Bartoshuk, L. M., Herz, R. S., Klatzky, R. L., & Merfeld, D. M. (2012). Sensation and perception. Sunderland, MA: Sinauer Associates.
• Luck, S. J., & Hollingworth, A. (2009). The role of attention in perceptual sensitivity: Evidence from psychophysical studies and event-related potentials. Attention, Perception, & Psychophysics, 71(4), 762-780. doi: 10.3758/APP.71.4.762

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