Differential Threshold: What It Is, And Methods To Study 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 able to notice, whether 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.
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 houses the concept of sensory thresholds.
A sensory threshold is understood to be a kind of psychological margin that delimits our capacity for sensation. This means that if a certain stimulus is below our ability 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, traditionally, has focused on the study of the two thresholds mentioned so far, especially the absolute threshold. However, the concept of differential threshold (UD), also called justly perceptible sensation, acquires great importance, which is defined as the distance between a fixed stimulus and a changing stimulus, whether its intensity is increased or decreased, 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 perceive it.
The differential threshold is a phenomenon that may depend on the circumstances. Thus, the person who is undergoing a psychophysical experiment may report feeling the changes one day and, when the experiment is performed again in another situation, despite the fact that the same physical changes in magnitudes occur, this person no longer perceives them. 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 ensure the survival of the newborn, mothers need to skillfully identify the voice of their children, 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 method of limits
The determination of the differential threshold can be done experimentally taking into account the following.
A subject can be asked to indicate whether he or she perceives differences between two stimuli on each trial of the experiment. To do this, it is necessary that there be a standard stimulus or one with a 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 security, it is necessary to do multiple tests, in order to have the maximum amount of information possible and ensure that the subject does not answer at random. 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 keep in mind that the subject will not always perceive E1 and E2 as equal, despite really 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 being different. This phenomenon is related to the Subjective Equality Point (PIS), which is the degree to which two stimuli are felt to be equal or not.
Method of constant stimuli
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. By not having direction, errors such as habituation and expectation are avoided.
Average error method
Is about one of the most classic methods used in Psychophysics. Using this method, the value of the stimulus is changed continuously, 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 the differential threshold
Below are some practical examples to understand the concept of differential threshold in greater depth.
1. Differentiate between two mounds of sand
We ask a person to keep their arms extended, with their hands open. The same amount of sand is placed in each hand.
Once this is done, the experiment can begin. Grains of sand are placed one by one in the right hand and The person is asked to indicate if they notice any difference.
2. Television volume
At some point in our lives we have had arguments over the volume of the television. There are those who want it high while others want it as low as possible.
A practical case that can be carried out in the living room is check at what volume you start to notice what is being said on television. In addition to obtaining the absolute threshold, you can know how many times it is necessary to press the button to notice changes in the volume.
3. Noisy neighbors
Parties can get out of control. Sometimes the neighbors complain, ask that the music be turned down and the host does so.
Partygoers notice the difference, and feel like 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
In each house it is cooked in different ways. There are those who abuse salt, others prefer to avoid it at all costs. Soup, a very common dish, is, in turn, one of the most different ways to be prepared.
It is for this reason that whoever prepared it for us may have made it too bland for our taste, although the host may even find it too salty.
