Differential threshold: what it is and study methods

Psychology has extracted a large 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, along with Ernst Heinrich, laid the foundations for psychophysics. His experiments have contributed to the understanding of sensory thresholds, that is, what people are able to notice, either not at all noticeable, or changes between two stimuli.

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

    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 embraces the concept of sensory thresholds.

    It is understood by sensory threshold to a kind of psychological margin that delimits our capacity for sensation. This means that if a certain stimulus is below our ability to hear it, such as too loose a sound, we say it is below our lower 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 so far, in particular the absolute threshold. However, the concept of differential threshold (DU), also called just perceptible sensation, which is defined as the distance between a fixed stimulus and a changing stimulus, either increased or decreased in intensity, when perceived, acquires great importance by the subject.

    To understand it more clearly, we understand what the differential threshold is the smallest change that needs to be made in a stimulus for the person to perceive.

    The differential threshold is a phenomenon which may depend on the circumstances. Thus, the person undergoing a psychophysical experience may indicate feeling the changes one day, and when they turn to experience the experience in another situation, even though the same physical changes occur in the magnitudes, that person does not perceive them. more. For this reason, it is necessary to repeat the experiments rigorously, the goal being to precisely delimit this threshold.

    Adaptively speaking, people we have developed the ability to discern between intensity and other elements of stimuli. For example, to ensure the survival of the newborn, mothers must skillfully identify their children’s voices, although to other people it may seem that all newborns have the same voice when they cry.

    Determination of the differential threshold by the limit method

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

    A subject can be asked to indicate whether he perceives differences between two stimuli in each trial of the experiment.. To do this, there must be a standard stimulus or one with an always fixed value (E1) and another stimulus whose intensity will vary throughout the experience or variable stimulus (E2). The task of the subject is to indicate when he feels that E1 and E2 are different, the changes in E2 can go both ways, that is, their value can be increased or decreased compared to E1.

    In order to be able to delimit the differential threshold with different degrees of precision and security, several repetitions must be performed, In order to be able to have as much information as possible and to ensure that the subject does not respond to chance. 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 E2 immediately below E1 (UB) divided by two.

    UD = (UA – UB) / 2

    It is important to note that the subject does not always perceive E1 and E2 as equal, even if they really are. This may be due to an illusion about the difference between these two stimuli, a random response, or simply perceiving them as if they are different. This phenomenon is linked to the point of subjective equality (PIS), which is the degree to which it feels or not equal to two stimuli.

      Constant stimuli method

      Unlike the previous case, using this method E1 is still a fixed value, however E2 changes its value randomly, i.e. it neither increases nor decreases gradually. In the absence of direction, mistakes such as habituation and waiting are avoided.

      Mean error method

      This is one of the most classic methods used in psychophysics. By this method, the value of the stimulus is changed continuously, until the sensation changes from not perceived to perceived and vice versa. This method can only be used for stimuli that can be changed continuously.

      Daily examples of the differential threshold

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

      1. Differentiate between two sand mounds

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

      Once this is done, the experiment can be started. 1-1 grains of sand are placed on the right hand and the person is asked to indicate if they notice a difference.

        2. TV volume

        At one point in our life we ​​had discussions about the volume of the television. Some want it high while others want it as low as possible.

        A case study that can be brought to the show is check at what volume you start to notice what is being said on TV. Besides getting the absolute threshold, you can how many times you have to press the button to notice the volume changes.

        3. Noisy neighbors

        Holidays can get out of hand. Sometimes the neighbors complain, ask for the music to be downloaded and the host does.

        Party attendees notice the difference and feel the volume has decreasedBut the neighbor who complained the first time comes back to ask for the music to be downloaded again.

        4. The soup is bland

        In each house it is cooked in different ways. Some people abuse salt, others prefer to avoid it anyway. Soup, a very common dish, is in turn one of the most different forms to prepare.

        It is for this reason that whoever prepared it for us may have made it too bland for our liking, although it may be too salty for the host.

        Bibliographical references:

        • Corso, JF (1963). A theoretical and historical examination of the concept of threshold. Psychological Bulletin, 60 (4), 356-370.
        • Flammer, J .; . Drance, S. M; Schulzer, M. (1984) Covariates of the long-term fluctuation of the differential threshold of light. Ophthalmology Archives, 102 (6): 880-882.
        • Heidelberger, M. (1993). The nature of the interior. Pittsburg, United States, University of Pittsburg Press.
        • Myers, D. (2006), 7th edition of Psychology. Pan American Medical Editorial.

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