What is Psychophysics?

Niki Foster
Niki Foster

Psychophysics is a subfield of psychology addressing the relationship between physical stimuli and subjective responses, or percepts. The term "psychophysics" was coined by the field's founder, Gustav Theodor Fechner, in 1860. Earlier scientists, including German physiologist Ernst Heinrich Weber and medieval scientist Alhazen, conducted similar experiments, though the field was not clearly defined until Fechner's work. Experiments can focus on any sensory system: hearing, taste, touch, smell, or sight.

Lights varying in brightness may be used in psychophysics experiments.
Lights varying in brightness may be used in psychophysics experiments.

Objectively measurable stimuli are used in psychophysics experiments, such as lights varying in brightness, or sounds varying in loudness. A threshold, or limin, is the point at which a subject can detect a stimulus, or a change in the stimulus. Stimuli falling under the threshold are considered sub-liminal or undetectable.

An absolute threshold, or detection threshold, is the point at which a subject can detect the presence of a stimulus, while a difference threshold is the magnitude of difference perceptible between two stimuli. For example, a difference threshold may be tested by asking a subject to adjust a sound until it is the same as another, and then measuring the difference between the two sounds. The point of subjective equality (PSE) is the point at which the subject considers two stimuli to be the same, while the just noticeable difference (JND) or difference limen (DL) is a difference between stimuli perceived 50% of the time.

Classical psychophysics experiments may take a number of forms. They may use the ascending method of limits, in which stimuli are presented beginning at a very low, undetectable level, then gradually increased to note the point, at which they become perceptible. Another method is the method of constant stimuli, in which stimuli are administered in random order rather than ascending order. The method of adjustment requires the subject to manipulate stimuli until they are just barely perceptible against a background, or until they are the same as or just barely different from another stimulus.

Newer methods in psychophysics experimentation include those called staircase procedures, first used by the Hungarian biophysicist Georg von Békésy in 1960. In experiments using staircase procedures, stimuli are first presented at a high, detectable level. The intensity is decreased until the subject makes a mistake in perceiving it. After the mistake, the scale is reversed, with intensity increasing until the subject responds correctly. At that point, the intensity is decreased again. The values for the reversals are then averaged. The staircase method helps experimenters narrow in on the threshold.

Niki Foster
Niki Foster

In addition to her role as a wiseGEEK editor, Niki enjoys educating herself about interesting and unusual topics in order to get ideas for her own articles. She is a graduate of UCLA, where she majored in Linguistics and Anthropology.

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Discussion Comments


I'm interested in how psychophysics is used to design electronic gadgets, appliances and even software. People who design these things need to know how it would be most useful and beneficial to consumers. So they need to know how it would appear to people who use them and the convenience of it. I think this career field is going to keep growing and will be one of the best paying career fields.

Theory wise though, the logic behind psychophysics seems to beat itself. If how we perceive everything is subjective, then even the results of these experiments are subjective. If everything we see, feel and understand is filtered through our mind, then is it really possible to know how close that is to reality or to perfection? Because even that reality is filtered through our mind!


@alisha-- I think this article is a great introduction to psychophsics for those who are not in the field and you've asked a really good and practical question.

I think the example you gave is related to psychophysics but it's not exactly how psychophysics is used. I personally think that the name of this field is kind of misleading because it implies that it has to do with psychology.

It's definitely related to the human psyche because it's about how we experience the world around us and we do that through our psyche but it's not about getting everyone to the same point, if that makes sense.

Psychophysics can help us understand how we perceive and react to different things. For example, some people like Pepsi, others prefer Coke and some are fine with both. The reason is because each person experiences these drinks differently. If you perceive their taste to be different from one another and that one is closer to your tastes than the other, you will choose that one over the other. This is psychophysics. It doesn't try to get people to drink Pepsi or Coke, it just wants to know why they do.

Do you see what I mean?


What is psychophysics used for? I mean, why would I want to know what my sensory thresholds are?

I think it's used in certain treatments because I had read in a magazine that in some psychological disorders, people can go in and out of different sensory stages. So they might have a really low sensory threshold in one stage and a really high one in another. The example that was given in that article was that in one disorder, doctors knew the patient was in one stage when they poked the patient's foot with a needle and received no response whatsoever.

Is this a good example of psychophysics? What else can psychophysics be used for though?

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