What Is the Absolute Threshold of a Stimulus?

Difference Between Absolute Threshold and Difference Threshold

What Is the Absolute Threshold of a Stimulus?

An absolute threshold is the lowest intensity of a stimulus that a person notices at least 50% of the time. A difference threshold is the least difference between two stimuli that a person can notice.


The absolute threshold is the minimum intensity of some stimulus that a person can notice with their senses. It is defined by Ernst Weber as the minimum or lowest intensity that a person will detect on at least half the trials in a test of the senses. 

How it is measured:

A person is exposed to a stimulus at varying intensities and then asked to state if they can detect the stimulus or not in each case. The lowest or minimum intensity that a person can detect at least 50% of the time is then the absolute threshold value.

The exact methods of the trials vary depending on which sense is being used and tested, for instance, taste versus vision. If taste is being tested then obviously the individual will have to taste some substance at varying strengths or intensities.

If a person is having the vision measured then, for example, a candle will be held at different distances and the absolute threshold determined. 


An example that illustrates an absolute threshold is when a person goes has a hearing test done. An individual has to listen for the tones which are of different intensities. This threshold is ly to change as a person becomes older since there is ly to be age-related hearing loss.

This is true for most of our senses which means that the actual value of the absolute threshold for each sense can change and is not the same for every person.

Absolute intensity can also be used when assessing the fitness of individuals and for comparing the fitness of different groups of people.


Knowing the absolute threshold can be very useful even for the development of certain food items. For instance, establishing the level as an indicator of the pungency of chili was suggested as a good way to know how much should be added to a food dish in order for customers to detect the taste of the chili.

Difference between Absolute threshold and Difference threshold?

An absolute threshold is the minimum level of intensity of a particular stimulus that a person can notice with their senses. A difference threshold is the minimum or least difference between stimuli that a person can notice.

The way absolute threshold is measured is that the lowest intensity noticed 50% of the time by a person is recorded. The way the difference threshold is measured is that an upper and a lower threshold are measured and the average of the two values is taken.

The absolute threshold is not a value a person noticing and recording a change of a stimulus. The difference threshold is noticing a change in the stimulus and noticing the smallest change.

The mean value is not used when measuring the absolute threshold. The mean value is used when measuring the distance threshold.

The absolute threshold is the minimum intensity that is recorded. The distance threshold is the minimum difference between the intensities that is recorded.

An example of an absolute threshold is when a person has a hearing test and hears sound of different intensities. An example of a difference threshold is when a person is asked to discriminate between two auditory tones.

Summary of Absolute Threshold Vs. Difference Threshold

  • The absolute and difference threshold are both ways to see how a person’s senses are working.
  • An absolute threshold is the lowest intensity of a stimulus that a person can detect at least half of the time.
  • A difference threshold is the minimum or lowest difference among intensities of a stimulus that a person can detect.

Associate Professor of Biology PhD in Quantitative Biology at in United StatesDr. Rae Osborn was educated in South Africa and the United States. She holds Honors Bachelor of Science degrees in Zoology and Entomology, and Masters of Science in Entomology from the University of Natal in South Africa.

She has received a PhD in Quantitative Biology from the University of Texas at Arlington as well as an AAS Degree in Information Network Specialist and an AAS in Computer Information Systems, at Bossier Parish Community College in Louisiana.Her skills lie in research and writing for a range of educational levels and teaching various Biology classes.

She has been trained as a lecturer, researcher and computer scientist. She has experience as a writer, researcher and as a college teacher, and is currently working as a freelance writer and editor.Her accomplishments include receiving tenure and being promoted to Associate Professor of Biology in the United States and publishing papers in peer-reviewed journals.

Her hometown is Pietermaritzburg in South Africa where her main interest and hobby is bird watching.

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Источник: http://www.differencebetween.net/science/difference-between-absolute-threshold-and-difference-threshold/

Absolute vs. Difference Threshold: AP® Psychology Crash Course Review

What Is the Absolute Threshold of a Stimulus?

Attention: This post was written a few years ago and may not reflect the latest changes in the AP® program. We are gradually updating these posts and will remove this disclaimer when this post is updated. Thank you for your patience! 

Sensation and Perception is possibly one of the less appreciated areas in psychology for the majority of high school and undergrad students because of its resemblance to physics and other hard sciences that commonly scare psychology students away.

This happens especially when weird terms Absolute Threshold, Difference Threshold, and Weber’s Law come up.

However, these themes are not as difficult as they may sound, and if you still fear psychophysics, read on in this Advanced Placement (AP) Psychology Crash Course Review to clear your doubts and understand what Absolute Threshold, Difference Threshold, and Weber’s Law are all about.

Why is Psychophysics Important Anyway?

If upon studying psychophysics you inevitably end up wondering why this is an important part of psychology, you are not being picky.

Wanting to know the relevance of each concept and theory is what all psychology students should seek, considering that psychology is a science that requires a lot of reflection and critical thinking.

So indeed, why is the study of Sensation and Perception important for the understanding of animal and human behavior?

First of all, there is the more technical and historical side: psychophysics was one of the first fields of psychology to use rigorous methods of study, giving to psychology a very scientific approach rather than a more philosophical one. This prepared the field for other studies that would treat psychology as a strict science that should be tested, measured and quantified.

Secondly, from a philosophical point of view, psychophysics shows that physical reality and psychological reality are not identical.

This was already a discussion in philosophy, but it was psychophysics that first came with scientific proof of that statement.

That is because psychophysics quantifies the relationship between physical stimuli and individual perception, building the bridge between the mental world and the material world.

What this all means is that the way we experience and interpret the world establishes our sense of reality.

If you’ve ever watched The Matrix, you may remember Morpheus questioning the main character’s reality: “What is real? How do you define real? If you’re talking about what you can feel, what you can smell, what you can taste and see, then real is simply electrical signals interpreted by your brain.”

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Sensation, Perception, and Thresholds

Although pretty scary, that quote from The Matrix helps us understand two concepts that are vital in psychophysics: bottom-up and top-down processing.

Bottom-up processing is when the information acquired in our sense receptors (sight, hearing, taste, touch and smell) goes to our brain to be interpreted.

Top-down processing is when our brain uses information that has already been brought by sensory systems to organize our experiences and expectations.

Together, they form what is called Sensation and Perception, a field of psychology that makes up for 6-8% of the AP® Psychology exam.

But what is a threshold and how does it relate to Sensation and Perception? Simply put, thresholds refer to limit values, and in this case, it means that our perceptions have limits. Take the intensity of a light bulb, for example.

There is a minimum value in its intensity for us to perceive the light. And if you increase its intensity, there is a minimum value for us to perceive any change in the light.

These minimum values are called absolute threshold and difference threshold.

Absolute Threshold

An absolute threshold is the smallest amount of stimulation needed for a person to detect that stimulus 50% of the time. This can be applied to all our senses:

  • The minimum intensity of light we can see
  • The lowest volume of a sound we can hear
  • The smallest concentration of particles we can smell
  • The smallest concentration of particles we can taste
  • The lightest touch we can feel

But what is that “50% of the time” part of the definition for? Why not 100% of the time?

That is because our absolute threshold can vary according to external and internal factors background noise, expectation, motivation and physical condition. It is easier to hear a sound when we are in perfect health, expecting to hear it in a quiet room than when we are tired, unaware of it and in a noisy street.

The affirmation that there is no single absolute threshold is called signal detection theory. Because our perception responses may vary, to find a person’s absolute threshold researchers conduct multiple tests until they find the amount that is perceived 50% of the time.

There is also another factor that influences the absolute threshold: sensory adaptation. Sensory adaptation happens when a stimulus remains the same for a long period of time, and our bodies stop recognizing it.

Think of entering a room where the air conditioner is really loud. In the beginning, the sound of the air conditioner may bother you, but after you’ve been in the room for a while, you’ll stop noticing it.

If somebody turns off the air conditioner, you’ll immediately notice the difference, even if you were not aware of its sounds before.

This is a biological response that makes total sense because if a stimulus is perceived for an extended period of time and nothing bad happens, then that stimulus is not dangerous and it can be ignored since it’s not worth spending energy to sense and perceive it. That is sensory adaptation.

Difference Threshold

A difference threshold is the minimum required difference between two stimuli for a person to notice change 50% of the time (and you already know where that “50% of the time” came from). The difference threshold is also called just noticeable difference, which translates the concept more clearly. Here are a few examples of difference thresholds:

  • The smallest difference in sound for us to perceive a change in the radio’s volume
  • The minimum difference in weight for us to perceive a change between two piles of sand
  • The minimum difference of light intensity for us to perceive a difference between two light bulbs
  • The smallest difference of quantity of salt in a soup for us to perceive a difference in taste
  • The minimum difference of quantity of perfume for us to perceive a difference in something’s smell

You may have already had the experience of turning up the TV or radio volume and not noticing a difference until a certain point. That is the difference threshold concept in action. If you don’t notice the difference, your difference threshold has not been reached yet.

To quantify the difference threshold, psycho-physicist Ernst Weber developed what is known as the Weber’s Law.

Weber’s Law states that rather than a constant, absolute amount of change, there must be a constant percentage change for two stimuli to be perceived as different.

In other words, the higher the intensity of a stimulus, the more it will need to change so we can notice a difference.

Imagine the TV/radio situation again, and imagine the manufacturers built a bad volume system in which each increase in volume corresponds to a constant increase in absolute (not percentage) amount.

You can notice a difference when you go from volume 1 from volume 3, for example, but you don’t perceive the same difference when the volume goes from 40 to 43.

According to Weber’s Law, for you to perceive the difference between volume 40 and 43 the same way you perceived the difference between volume 1 and 3 (an increase of 300%), volume 40 would have to go up to 120 (the same increase of 300%).

Sensation and Perception on the Exam

On the exam, you might be asked to define and compare both thresholds, stating how they can be applied to a concrete situation. For example, describe how each one could be used in the development of a new set of speakers and headphones.

Now that you’ve mastered this AP® Psychology Crash Course Review, you could answer that the absolute threshold can be used to set the minimum volume, as it would be pointless to insert a volume that nearly nobody can hear.

The difference threshold can be used to set a smart, user-friendly system in which a raise in each volume bar would be perceived as a constant increase in volume because it would be proportional to the previous amount, just as stated in Weber’s Law.

However, it is also possible that you encounter a broader question on the topic of Sensation and Perception, this one:

Describe the psychological concept of expectancy or set. Discuss a specific example of how each expectancy or set affects each of the following.

A possible answer to this question is top-down processing, which influences our expectations and ultimately our perceptions. Another answer could refer to signal detection theory because it is easier for us to detect a stimulus if we are expecting it.

Psychophysics can seem intimidating, but you’re surely more confident about it now that you know what sensation and perception are and the difference between absolute threshold and difference threshold. So, what is the importance of studying human senses for you? How do you relate your individual perceptions of reality to the external, material reality? Share in the comments below!

Looking for more AP® Psychology practice?

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