Differential threshold: what it is, and methods to study it

Differential threshold is one of the most important concepts in psychophysics.

Psychology has extracted a wide repertoire of knowledge through experimentation.

Authors such as William James or Gustav Theodor Fechner postulated that stimuli induce physiological and emotional changes. These two scientists, together with Ernst Heinrich, laid the foundations of psychophysics. Their experiments contributed to the understanding of sensory thresholds, i.e. what people are able to notice, whether it is the slightest perceptible or changes between two stimuli.

In this article we will focus on the concept of differential threshold, trying to explain how it can be calculated.The concept of differential threshold, trying to explain how it can be calculated and giving some examples from everyday life.

What is differential threshold?

Psychophysics is the science that studies the relationship between physical phenomena and their psychological interpretation. For this reason, it is not surprising that it is this branch of psychology that houses the concept of sensory thresholds.

A sensory threshold is understood as a sort of psychological psychological margin that delimits our capacity for sensation.. This means that if a certain stimulus is below our capacity to feel it, such as a sound that is too soft, we say that it is below our lowest sensory threshold (absolute threshold or lower limit). If, on the other hand, the intensity is very high and can even be painful, we say that it is above our highest sensory threshold (terminal threshold or upper limit).

Psychophysics has traditionally focused on the study of the two thresholds mentioned above, especially the absolute threshold. However, the concept of differential threshold (DUT), also called just perceptible sensation, acquires great importance, which is defined as the distance between a fixed stimulus and a changing stimulus, either increased or decreased in intensity, when perceived by the subject.

To understand it more clearly, we understand that the differential threshold is the smallest change that must be made between a fixed stimulus and a changing stimulus. the smallest change that must be made in a stimulus for the person to be able to perceive it..

The differential threshold is a phenomenon that may depend on the circumstances. Thus, a person undergoing a psychophysical experiment may indicate that he/she feels the changes one day and, when the experiment is repeated in another situation, despite the fact that the same physical changes in the magnitudes occur, this person no longer perceives them. For this reason, it is necessary to rigorously repeat the experiments aimed at accurately delimiting this threshold.

Adaptively speaking, people have developed the ability to have evolved the ability to discern between intensity and other elements of stimuli.. For example, in order to ensure the survival of the newborn, mothers need to skillfully identify the voice of their infants, even though, to other people, it may seem that all newborns have the same voices when they cry.

Determination of the differential threshold by the boundary method

The determination of the differential threshold can be done experimentally with the following in mind.

A subject can be asked to indicate whether he/she perceives differences between two stimuli on each trial of the experiment.. For this, it is necessary to have a standard stimulus or stimulus with an always fixed value (E1) and another stimulus whose intensity will vary throughout the experiment or variable stimulus (E2). The subject's task is to indicate when he/she feels that E1 and E2 are different; modifications in E2 can go in both directions, i.e., its value can be increased or decreased with respect to E1.

In order to delimit the differential threshold with a greater degree of precision and certainty, it is necessary to perform multiple trials, it is necessary to carry out multiple testsIn order to have as much information as possible and to make sure that the subject does not respond randomly. The differential threshold (UD) is equivalent to the distance between the stimulus detected E2 as immediately greater than the standard E1 (high threshold, UA) and the E2 immediately less than E1 (UB), divided by two.

UD = (UA - UB) / 2

It is important to note that the subject will not always perceive E1 and E2 as the same, even though they really are. This may be due to an illusion as to the difference between these two stimuli, a random response or simply because he/she really perceives them as being different. This phenomenon is related to the Point of Subjective Equality (SIP), which is the degree to which two stimuli are felt to be the same or not.

Method of constant stimuli.

Unlike the previous case, by means of this method E1 remains a fixed value, but E2 changes its value randomly, i.e., it does not increase or decrease progressively.. As there is no direction, errors such as habituation and expectation are avoided.

Average error method

This is one of the most one of the most classical methods used in psychophysics.. By this method, the value of the stimulus is changed continuously, until the sensation goes from not being perceived to being perceived and inversely. This method can only be used for stimuli that can be continuously modified.

Everyday examples of differential threshold

The following are some practical examples for a deeper understanding of the concept of differential threshold.

1. Differentiating between two sand mounds

We ask a person to hold their arms outstretched, with their hands open. The same amount of sand is placed in each hand.

Once this is done, the experiment can begin. One by one, grains of sand are placed in the right hand and the person is asked to place the same amount of sand in each hand. the person is asked to indicate if he/she notices any difference..

Television volume

At some point in our lives we have had arguments over the volume of the television. Some people want it loud while others want it as low as possible.

A practical case that can be carried out in the living room is to check the volume at which check the volume at which you start to notice what is being said on the television.. In addition to obtaining the absolute threshold, you can see how many times you need to press the button to notice changes in the volume.

3. Noisy neighbors

Parties can get out of control. Sometimes neighbors complain, ask for the music to be turned down and the host does so.

Partygoers notice the difference, and feel that the volume has decreased.However, the neighbor who complained the first time comes back to ask for the music to be turned down again.

4. The soup is bland

Every house cooks in a different way. Some people overuse salt, others prefer to avoid it at all costs. Soup, a very common dish, is, at the same time, one of the dishes that can be prepared in the most different ways.

It is for this reason that whoever has prepared it for us may have made it too bland for our taste, even though it may even be too salty for the host.

Bibliographical references:

• Corso, J. F. (1963). A theoretical-historical review of the threshold concept. Psychological Bulletin, 60(4), 356-370.
• Flammer, J.; . Drance, S. M; Schulzer, M. (1984) Covariates of the Long-term Fluctuation of the Differential Light Threshold. Archives of Ophthalmology, 102(6):880-882.
• Heidelberger, M. (1993). Nature from Within. Pittsburgh, USA, University of Pittsburgh Press.
• Myers, D. (2006), Psychology 7th edition. Editorial Médica Panamericana.