Psychophysics: the beginnings of psychology

Today, it is not uncommon to hear about psychology as a science or the figure of the psychologist in various fields related to the study of mind and behavior. However, it is a relatively young scientific discipline and that he encountered several difficulties in presenting himself.

And it is that although the human mind has interested man since antiquity, it was not until 1879 that Wilhelm Wundt created the first laboratory of psychology and psychology like science. At this time and even before that, the beginnings of psychology are linked to the first attempts to measure the relationship between physical and mental aspects; that is to say in psychophysics.

    What is psychophysics?

    Psychophysics is included in the branch of psychology whose main object of study is the relationship between external stimulation and its qualities and a subject’s perception of this stimulation.

    It is one of the first types of studies to be carried out in a scientific way in which psychological aspects such as sensation and its evaluation have been analyzed. The measurement of psychophysical aspects required high precision instruments and the development of different techniques which would allow obtaining valid and reliable data, being in fact psychophysics the direct precursor of psychometry.

    In psychophysics, models began to be developed in which a numerical value began to be attributed to the characteristics of stimuli and their perception, being a pioneer in the quantitative research of mental phenomena. In other words, it measures the behavioral response to the physical stimulus. Psychophysics was born initially dedicated to the study of visual perceptionBut later, it will be broadened to eventually extend to the study of the relationship between the physiological and the psychic.

    Stimulation is believed to generate physiological activation which ultimately causes sensation, although the two components separately also have the potential to generate sensations on their own.

    Psychophysics used different methods to measure sensation. Among them we find the description on the part of the subject of the perceived thing, the recognition of this, the detection, the perception of the magnitude or the search for the stimulus.

      The parents of psychophysics

      While precursors exist in ancient Greece and among many philosophers such as Hume, it is considered that the main fathers of psychophysics were Weber and Fechner.

      The first of them is particularly recognized for his experiments related to the threshold of detection of the stimulus. Weber studied the double threshold of detection, or the level of separation required for a stimulus to be captured in fragmented form (he used a compass on the subject’s skin, and analyzed when he noticed a single stimulus and when he was able to discern the two councils as separate stimuli.

      These experiments were broadened and deepened by Fechner, who would draft the Weber-Fechner law and analyze phenomena such as the absolute threshold or the minimum stimulation necessary to arouse a sensation and the differential threshold, previously proposed by Weber, in which the difference necessary to notice changes in the perception of a stimulus is studied.

      Weber’s law and the reformulations of Fechner and Stevens

      The research of Weber, then that of Fechner, made it possible to formulate one of the first psychophysical laws. More precisely, it is established that we can differentiate the different stimuli according to the intensity with which they are presented. We distinguish between relative changes: we may not grasp the difference between two different stimuli occurring at the same time unless there is a specific change in the intensity of these.

      But if the intensity of the stimulus itself increases, the relative difference will also have to be increased to capture the existence of two different perceptions. Thus, this capacity for discernment requires that this increase in intensity be constant, as a function of the value of the variation compared to the starting point.

      For example, if we touch two raindrops very close together, we may need a small separation to notice two sensations while if what touches us are the rays of a pipe, the separation between them should be slightly larger. to perceive how different elements.

      This law would be exceeded and modified by the reformulations of Fechner and Stevens, Which would eventually identify that sometimes an increase in the magnitude of the stimulus does not generate a proportional change in perception but sometimes generates a much larger or smaller change in perception than expected.

        original methodology

        The methods used during the early days of psychophysics were indirect by working from the measurement of the physical stimulus and obtaining it from the sensation. It is considered that the sensation could not be measured directly, Being associated only with the magnitude of the stimulus. Three main types of methods stand out in this type of psychophysics.

        Limits method

        The experimenter presents series of different stimuli, which may or may not be captured by the subject studied. The experimenter manipulates the intensity of the stimulus, having to tell the candidate whether he is able to perceive the stimulus or whether a comparison stimulus is more, equal or less intense. The stimuli have a continuous ascending or descending order, going in series. There may be addiction or expectations.

        Mean error method

        This type of methodology is based on manipulating the stimulus until a change in sensation is generated, adjusting the stimulus according to the subject’s response. Although it is comfortable and simple because it is the candidate himself who regulates the stimulation, it can generate errors depending on the growth expectation of the stimulus or it decreases in intensity and the perception is biased.

        Constant stimuli method

        This methodology of classical psychophysics is based on the use of default intensities which remain constantBut on the contrary, in the method of limits the intensity of the stimulus varies at random. This is generally the most used method because it minimizes errors and bias, although it generates more fatigue.

        direct methodology

        Besides Weber and Fechner, Stevens is another of the great pioneering authors of psychophysics. This author would consider the need for direct measurements of sensation, creating assessment scales centered on the subject’s own subjective sensation and his way of evaluating this perception. The methods proposed by Stevens, which are later those which continued to be used in practice, would be as follows

        1. Category method

        Similar to a Likert-type scale, a series of stimuli is presented to the subject who must be classified according to the different categories offered to him.

        2. Method for estimating the reason

        Two stimuli of the same type are presented to the candidate at the same time, in order to assess the numerical relationship between the two.

        3. Method of production of the reason

        The candidate must generate a stimulus from an initial stimulus and a proportionality report that the examiner presents to him. For example, the subject must generate a light twice as bright as that presented to him.

        4. Amplitude estimation method

        By estimating the magnitudes, the experimenter presents the candidate with a series of stimuli that the subject must evaluate numerically, Show an example to get a rough idea of ​​the value of a sample of the stimulation.

        5. Method of producing magnitude

        This methodology is based on the explored subject generating the level of stimulation corresponding to the intensity proposed by the experimenter (for example, the intensity of the sound of the voice).

        6. Interval estimation method

        In him, the subject has estimate the difference between two stimuli presented.

        7. Interval production method

        This method assumes that the candidate recreates an interval in the stimuli, dividing them into different parts.

        Effect on other branches of psychology

        Psychophysics allow the start of the qualitative study of psychological aspects such as perceptions. Ultimately, this initiative would allow him to eventually develop psychometrics, which in turn allowed the generation of scales and methodologies to measure much more cognitive and abstract aspects from performance in tasks related to these elements. . For example, personality traits, skills and attitudes or intelligence.

        Certain branches which have benefited from the contributions of psychophysics are clinical, professional or educational psychology. In fact, it can even be applied to things like physiological activation caused by fear.

        Bibliographical references:

        • Higueras, B. and Muñoz, JJ (2012). Basic psychology. CEDE PIR preparation manual, 08. CEDE: Madrid.
        • Goldstein, EB (2006). Sensation and perception. 6th edition. Debate: Madrid.
        • Fonts, S. and Fontes AI (1994). Theoretical considerations on psychophysical laws. Tower. of psychology. Gral. I Aplic., 47 (4), 191-195. National Distance Learning University (UNED).
        • University of Barcelona (sf) Classical and contemporary psychophysics. [En línea]. Available at:

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