Differential threshold: what it is, and methods for studying it

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. His experiments contributed to the understanding of sensory thresholds, that is, what people are capable of noticing, be it the slightest perceptible or changes between two stimuli.

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

• Related article: "Sensory thresholds: what they are and how they define our perception"

What is the differential threshold?

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

Sensory threshold is understood to be a kind of psychological margin that delimits our capacity for sensation. This means that if a given stimulus is below our ability to feel it, such as a sound too loose, we say that it is below our lower sensory threshold (absolute threshold or limit lower). 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, traditionally, has focused on the study of the two thresholds mentioned up to here, especially the absolute threshold. However, the concept of differential threshold (UD), also called just perceptible sensation, which is defined as as the distance between a fixed stimulus and a changing stimulus, either increasing or decreasing its intensity, when it is perceived by the subject.

To understand it more clearly, we understand that the differential threshold is 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 can depend on the circumstances. Thus, the person to whom a psychophysical experiment is being passed may indicate feeling the changes one day and, when do the experiment in another situation, despite the fact that the same physical changes in the magnitudes occur, this person no longer changes them perceives. For this reason, it is necessary to rigorously repeat the experiments whose objective is to accurately delimit this threshold.

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

Determination of the differential threshold by the limits method

The determination of the differential threshold can be done experimentally taking into account the following.

A subject may be asked to indicate whether he perceives differences between two stimuli on each trial of the experiment.. For this, it is necessary that there is a standard stimulus or 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 feels that E1 and E2 are different. Modifications in E2 can go in both directions, that is, 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 safety, it is necessary to carry out multiple tests, in order to have the maximum amount of information possible and ensure that the subject does not answer randomly. The differential threshold (UD) is equivalent to the distance between the detected stimulus E2 as immediately greater than the E1 standard (high threshold, UA) and E2 immediately less than E1 (UB), divided by two.

UD = (AU - UB) / 2

It is important to take into account that the subject will not always perceive E1 and E2 as equal, despite actually being so. This may be due to an illusion as to the difference between these two stimuli, a random response, or simply because he actually perceives them as different. This phenomenon is related to the Subjective Equality Point (PIS), which is the degree to which two stimuli are felt or not to be the same.

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Constant stimuli method

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

average error method

Is about one of the most classical methods used in Psychophysics. Using this method, the value of the stimulus is continuously changed, until the sensation goes from not being perceived to being perceived and vice versa. This method can only be used for those stimuli that can be modified continuously.

Everyday Examples of Differential Threshold

Below are some practical examples to better understand the concept of differential threshold.

1. Differentiate between two mounds of sand

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

Once this is done, the experiment can be started. Grains of sand are placed one by one in the right hand and the person is asked to indicate if they notice any difference.

• You may be interested in: "Gustav Theodor Fechner: biography of the father of psychophysics"

2. television volume

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

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

3. Noisy neighbors

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

Partygoers notice the difference, and feel the volume has droppedHowever, the neighbor who complained the first time returns to ask for the music to be turned down.

4. the soup is bland

Every house cooks in different ways. There are those who abuse salt, others prefer to avoid it at all costs. The soup, a very common dish, is, in turn, one of the ones that has the most different ways of being prepared.

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

Bibliographic 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. Panamerican Medical Editorial.