Psychophysics: the beginnings of Psychology

April 10, 2024

Nowadays it is not strange to hear about psychology as a science or the figure of the psychologist in various fields related to the study of mind and behavior. But nevertheless, it is a relatively young scientific discipline and that he encountered various difficulties to arise.

And is that although the human mind has interested man since ancient times, it was not until 1879 when Wilhelm Wundt created the first laboratory of psychology and established psychology as a science. At that 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 psychophysics .

Related article: "History of Psychology: authors and main theories"

What is psychophysics?

Psychophysics is understood as the branch of psychology whose main object of study is the relationship between external stimulation and its qualities and the perception of a subject of such stimulation.

It is one of the first types of studies that were carried out in a scientific manner in which psychological aspects such as sensation and the evaluation of it were analyzed. The measurement of psychophysical aspects required highly accurate instruments and the elaboration of different techniques that allow the obtaining of valid and reliable data, being psychophysics in fact the direct precursor of psychometrics.

In psychophysics they began to develop models in which they began to assign a numerical value to the characteristics of the stimuli and the perception of these, 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 in a beginning dedicated to the study of visual perception , but later it will be enlarged so that it ended up extending to the study of the relationship between the physiological and the psychic.

It is assumed that the stimulation generates a physiological activation that ends up causing a sensation, although both components separately also have the potential to generate sensations by themselves.

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

Related article: "What is Physiological Psychology?"

The parents of psychophysics

While there are precursors in ancient Greece and numerous philosophers such as Hume, it is considered that the main parents of psychophysics were Weber and Fechner .

The first one is especially recognized for its experiments related to the stimulus detection threshold. Weber investigated the threshold of dual detection, or the level of separation necessary for a stimulus to be captured in a fragmented way (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 points as separate stimuli.

These experiments were extended and deepened by Fechner, who would elaborate the law of Weber-Fechner and would analyze phenomena like the absolute threshold or the minimum of stimulation necessary to awaken a sensation and the differential threshold, previously proposed by Weber, in which the necessary difference is studied so that they notice changes in the perception of a stimulus.

Weber's law and the reformulations of Fechner and Stevens

Weber's investigations, and later Fechner's investigations, made it possible to formulate one of the first psychophysical laws. Specifically, it is established that we can differentiate between different stimuli depending on the intensity with which they present themselves. We distinguish between relative changes: we can not grasp the difference between two different stimuli that occur at the same time unless there is a concrete change in the intensity of these.

But if the intensity of the stimulus itself increases, there will also be an increase in the relative difference to grasp the existence of two different perceptions. Thus, this capacity for discernment requires that said increase in intensity be constant, based on the value of the variation with respect to the starting point.

For example, if we get two drops of rain very close together we may need a small separation to notice two sensations, while if we are the jets of a hose the separation between them should be somewhat larger to be perceived as different elements.

This law would be overcome 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 perceptive change much greater or much lower than expected.

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Original methodology

The methods used during the first moments of psychophysics were indirect when working from the measurement of the physical stimulus and obtaining the sensation from it. It is considered that the sensation could not be measured directly , being only associated with the magnitude of the stimulus. In this type of psychophysics there are three major types of methods.

Limits method

The experimenter presents series of different stimuli, which will be or not captured by the subject studied. The experimenter manipulates the intensity of the stimulus, the examinee having to say if he is able to perceive the stimulus or if a comparison stimulus is more, equal or less intense . The stimuli have a continuous increasing or decreasing order, going in series. There may be habituation or expectations.

Average error method

This type of methodology is based on the manipulation of the stimulus until a sensation change is generated, adjusting the stimulus according to the response of the subject. While it is comfortable and simple since it is the examinee himself who regulates the stimulation, can generate errors based on the expectation that the stimulus will grow or decrease in intensity and perception is biased.

Method of constant stimuli

This methodology of classical psychophysics is based on the use of predetermined intensities that remain constant , but unlike the limit method, the intensity of the stimulus varies randomly. It is usually the most used method since it allows to minimize errors and biases, although it generates more fatigue.

Direct methodology

In addition to Weber and Fechner, another of the great pioneering authors of psychophysics is Stevens. This author would consider the need for direct measurements of the sensation, creating estimation scales centered on the subjective sensation of the subject and his way of assessing that perception. The methods proposed by Stevens, which subsequently are those that have continued to be used in practice, would be the following

1. Method of the categories

Similar to a Likert-type scale, a series of stimuli are presented to the subject that must be classified according to various categories that are proposed.

2. Reason estimation method

Two stimuli of the same type are presented to the examinee at the same time, the latter having to assess the numerical relationship that exists between the two.

3. Reasons production method

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

4. Magnitude estimation method

In the estimation of magnitudes the experimenter presents to the examinee a series of stimuli that the subject must assess numerically , presenting an example so that you have an approximate idea of the value of a sample of the stimulation.

5. Method of production of quantities

This methodology is based on the fact that the explored subject generates the level of stimulation corresponding to the intensity that the experimenter proposes (for example, the intensity of the sound of the voice).

6. Interval estimation method

In it the subject must estimate the difference between two presented stimuli .

7. Method of production of intervals

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

Effect in other branches of Psychology

Psychophysics allowed the beginning of the qualitative study of psychological aspects such as perceptions . In the long run, this initiative would allow psychometrics to end up gestating, which in turn allowed for the generation of scales and methodologies that allow us to measure much more cognitive and abstract aspects based on performance in tasks related to these elements. For example personality traits, aptitudes and attitudes or intelligence.

Some branches that have benefited from the contributions of psychophysics are clinical, work or educational psychology. In fact, it can even be applied to elements such as physiological activation triggered by fear.

Bibliographic references:

Higueras, B. and Muñoz, J.J. (2012). Basic Psychology CEDE Preparation Manual PIR, 08. CEDE: Madrid.

Goldstein, E.B. (2006). Sensation and Perception 6th edition. Debate: Madrid.

Fontes, S. and Fontes A.I. (1994). Theoretical considerations on psychophysical laws. Rev. de Psicol. Gral. Y Aplic., 47 (4), 191-195. National University of Distance Education (UNED).