If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Absolute threshold of sensation

The "absolute threshold of sensation" refers to the minimum intensity of a stimulus that a person can detect half the time. This threshold is not fixed, but varies from person to person and can be influenced by psychological factors, such as expectations, motivation, and alertness. The absolute threshold is different from the "difference threshold," which measures the smallest difference in stimulation that can be detected.

Want to join the conversation?

  • aqualine ultimate style avatar for user fiahmed92
    I am confused about absolute threshold and difference threshold. When talking about the difference threshold around , is it basically the point in time when something is noticeably brighter - starting point of brightness? whereas the absolute threshold is the minimum intensity of a stimulus to detect another stimulus? are they both for 50% of the time? thanks in advance.
    (13 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user Connor
    Hello, I'm a little confused about the absolute threshold. It sounds as if the "absolute threshold of sensation" is actually about perception... It is about when someone detects a stimulus, not when a sensory system is activated (which is why mental state is important). Is the absolute threshold where sensory systems are reliably activated, or is it instead where an individual reliably notices the stimulus?
    (11 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user Diana Abbas
    The absolute threshold here is presented as the threshold of conscious perception i believe, which is different. the absolute threshold is just about sensation, but she makes it seem like its about perception...no?
    (9 votes)
    Default Khan Academy avatar avatar for user
  • purple pi purple style avatar for user Patrick Scollard
    When you draw the graph around the minute mark, you keep talking about the absolute threshold being at 50%, but on the Y-axis it looks like you drew 60%? I believe it's supposed to be at 50% as you verbally say this in the video, is that correct?
    (5 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user tathyapatel98
    I am reading a book and it defines two concepts, absolute threshold, and threshold for conscious perception. It mentions that absolute threshold is the minimum stimulus energy that is needed to activate the sensory system. The threshold for conscious perception is defined as the minimum stimulus required to consciously perceive the stimulus. They never mention anything about 50%. I am getting confused between these two concepts and absolute threshold of sensation described in the video. Can someone please explain the difference between all these concepts?
    (5 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user Arya Dadhania
    I understand that the JND is the difference between two stimulus that one can detect with 50% intensity. But, my question is, lets say we are performing an experiment to plot a graph for Absolute threshold, now we preset a baseline sound into the headphones(in the background) at about certain intensity and then now we measure the accuracy for each detectable change in intensity. So I think in that case we are essentially changing the experiment which would measure the change in two stimuli hence it would give us JND. So in reality is measuring Absolute threshold mean to set the baseline/background intensity at zero?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • marcimus pink style avatar for user Booi
      Watch the absolute threshold of sensation video. It explains that dI/I = K meaning change in intensity has a directly proportional relationship with the overall intensity. So if the baseline background noise is present, you will need higher dI to differentiate two stimuli.
      (1 vote)
  • starky tree style avatar for user goosh goosh 2008
    really need to fix the audio levels.
    (2 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user ninacharlot049
    I was reading through my Kaplan books and it explains that there is a threshold of sensation and a threshold of perception and that a subliminal message is when a stimulus passes the threshold of sensation but not the threshold of perception.
    Please clarify!
    (2 votes)
    Default Khan Academy avatar avatar for user
  • piceratops ultimate style avatar for user Darmon
    Who is the speaker in this video?
    (1 vote)
    Default Khan Academy avatar avatar for user
  • purple pi purple style avatar for user brewbooks
    Can I think of the absolute detection threshold for a yes/no test (such as tone present/ tone absent) as the point where the responses are just above chance?
    (1 vote)
    Default Khan Academy avatar avatar for user

Video transcript

- [Voiceover] The absolute threshold of sensation is the minimum intensity of a stimulus that is needed to detect a particular stimulus 50% of the time. So it is the lowest level of any stimulus that we can generally detect. And the 50% of the time clause here is actually really important. And this is for a number of reasons. One is individual differences. Simply put, at really low levels of a stimulus, some subjects can detect it while others cannot. There also might be differences within an individual. Think about maybe a time when your friend asks if you heard a sound, and you think maybe you did, but you're not entirely sure. Well that's what this 50% helps us take into account. So rather than asking, "What is the absolute "lowest sound a person is ever capable of hearing?" We want to know what is the lowest level of sound or light that a person can reliably hear or see. And let me try to graph this to make it look a little clearer. So on the X-axis we'll put Intensity, and we'll have lower intensity on one side, and higher intensity on the other. And so for things like sound, a lower intensity would be a very quiet sound, or as a higher intensity sound would be a much louder one. And then on the Y-axis I'm going to put Percentage of Correct Detections. And what that's referring to is actually something you may have experienced yourself when you were in elementary school. One thing that nurses can do in elementary school are these sound tests. And the way that they did them back when I was in school, was that they'd put these large headphones on your head, and then they'd play tones of different intensities into each of your ears. And the only thing that you as a listener had to do was raise your hand, either your left hand or your right hand when you heard a tone in either your left or right ear. And from the sounds they played, there were probably some that I correctly detected 100% of the time. I always heard them. I always raised my hand. But it is possible that I did not correctly identify all of the sounds 100% of the time. And that's what this Y-axis is referring to. And so imagine that this is you, and you have these headphones on, and that you're going through these same tests, and sometimes a sound is presented, and other times it isn't, but all the sounds are of different intensity. Well if you were to graph the responses, you might wind up with something like this, where the higher the tone is, you're more likely to identify it. But as it gets lower, you're less reliable in your judgement. And that 50% mark would be our absolute threshold of sensation. Before we move on, I do want to mention that the absolute threshold of sensation is different from a concept that has been talked about in other videos. And that's the difference threshold, or the just noticeable difference. And what the difference threshold is referring to, is the smallest difference in stimulation that can be detected 50% of the time. So imagine that you have a light with a dimmer switch on it, and it's really sensitive. And imagine that you're rotating that switch really slowly, and so the light is gradually increasing in intensity. The difference threshold would be the point between your starting point, and when you were able to perceive that the light was brighter. And I want you to keep this in mind, because I think that these concepts are pretty easy to mix up. And while they are related to each other, they are actually referring to different things. Looking back at our graph here, you might get the impression that the absolute threshold would be some kind of fixed, unchanging number. But it actually turns out that it can be influenced by a number of different factors. In particular, it can be influenced by a number of different psychological states. So let's think about this in terms of detecting a text message when your phone is on vibrate, and either it's in your bag, or maybe it's on a desk nearby. What are some things that might influence whether or not you will detect that your phone is buzzing? Well one thing that might influence whether or not you hear it is whether or not you are expecting a text. Also, our experience with that particular phone could influence it. Is it a new phone? Or are you really familiar with the particular sound that it makes when it vibrates against a wooden table, or against your cloth bag? How motivated we are can also have a huge effect on whether or not we detect something. So let's say that I've texted someone who I'm interested in to see whether or not they want to go on a date. So in this case, not only am I expecting a text, but I'm also really motivated to get it, because it's important for me to see the response. Another thing that might influence whether or not I hear the text message is alertness, meaning that I'm much more likely to notice it when I'm awake, as opposed to when I'm drowsy and half asleep on the couch. And before we move on, I also want to take a moment to talk about a term that's used to describe stimuli that we cannot detect 50% of the time, and that's subliminal. And maybe you've heard about subliminal messages before, and that's what this is referring to. It's referring to stimuli that is below our absolute threshold of sensation.