Nowadays it is not strange to hear about psychology as a science or about the figure of the psychologist in various fields linked to the study of the mind and behavior. However, It is a relatively young scientific discipline and that he encountered various difficulties to emerge.
And although the human mind has interested man since ancient times, it was not until 1879 when Wilhelm Wundt created the first psychology laboratory and psychology was established 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.
Psychophysics is understood to be the branch of psychology whose main object of study is the relationship between external stimulation and its qualities and a subject’s perception of said stimulation.
It is one of the first types of study that were carried out scientifically in which psychological aspects such as the sensation and the evaluation made of it were analyzed. The measurement of psychophysical aspects required highly precise instruments and the development of different techniques that would allow valid and reliable data to be obtained, in fact psychophysics being the direct precursor of psychometrics.
In psychophysics, models began to be developed in which a numerical value began to be assigned to the characteristics of the stimuli and their perception, pioneering the quantitative research of mental phenomena. In other words, it measures the behavioral response to physical stimulation. Psychophysics was originally born dedicated to the study of visual perception but later it will be expanded so that it ended up extending to the study of the relationship between the physiological and the psychological.
It is assumed that stimulation generates a physiological activation that ends up causing a sensation, although both components separately also have the potential to generate sensations by themselves.
The psychophysics has used different methods to measure sensation. Among them we find the description by the subject of what is perceived, its recognition, detection, perception of the magnitude or the search for the stimulus.
The fathers of psychophysics
Although there are precursors in ancient Greece and in numerous philosophers such as Hume, it is considered that The main fathers of psychophysics were Weber and Fechner.
The first of them is especially recognized for his experiments related to the stimulus detection threshold. Weber investigated the dual detection threshold, 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 expanded and deepened by Fechner, who would elaborate the Weber-Fechner law and would analyze phenomena such as the absolute threshold or the minimum stimulation necessary to awaken 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
Weber’s research, and later Fechner’s research, made it possible to formulate one of the first psychophysical laws. Specifically, it is established that we can differentiate between different stimuli based on intensity with which they are presented. We distinguish between relative changes: we may not capture the difference between two different stimuli that are presented at the same time unless there is a specific change in their intensity.
But if the intensity of the stimulus itself increases, the relative difference will also have to increase to capture 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 touch two raindrops very close together, we may need a small separation to notice two sensations, while if what we touch are the jets of a hose, the separation between them should be somewhat greater to be able to perceive them as different elements.
This law would be surpassed and modified by the reformulations of Fechner and Stevens which would end up identifying that sometimes an increase in the magnitude of the stimulus does not generate a proportional change in perception but sometimes generates a perceptual change much larger or much smaller than expected.
Original methodology
The methods used during the first moments of psychophysics were indirect by working from the measurement of the physical stimulus and obtaining the sensation from this. 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, three main types of methods stand out.
Limits method
The experimenter presents series of different stimuli, which will or will not be captured by the subject studied. The experimenter manipulates the intensity of the stimulus, with the examinee having to tell whether he is able to perceive the stimulus or whether a comparison stimulus is more, the same, 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 change in sensation is generated, adjusting the stimulus depending on the subject’s response. Although 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 the 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 limits method, the intensity of the stimulus varies at random. It is usually the most used method since it allows errors and biases to be minimized, 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 to perform direct measurements of the sensation, creating estimation scales focused on the subject’s own subjective sensation and his or her way of evaluating said perception. The methods proposed by Stevens, which have subsequently continued to be used in practice, would be the following
In a similar way to a Likert-type scale, a series of stimuli are presented to the subject who must classify them according to various categories proposed.
2. Ratio estimation method
Two stimuli of the same type are presented to the examinee at the same time, and he or she has to assess the numerical relationship that exists between them.
3. Reason production method
The examinee must generate a stimulus from an initial stimulus and a proportionality relationship that the examiner presents to you. For example, the subject has to generate light twice as bright as what is presented to them.
4. Magnitude estimation method
In the estimation of magnitudes the experimenter presents the examinee with a series of stimuli that the subject must evaluate numerically presenting an example so that you have a rough idea of the value of a sample of the stimulation.
5. Method of production of magnitudes
This methodology is based on the explored subject generating 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. Interval production method
This method involves the examinee recreating an interval within the stimuli, dividing them into different parts.
Effect on other branches of Psychology
The psychophysics allowed the beginning of the qualitative study of psychological aspects such as perceptions. In the long run, this initiative would allow psychometrics to emerge, which in turn allowed the generation of scales and methodologies that allow measuring much more cognitive and abstract aspects based on performance in tasks linked to said 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 caused by fear.
Bibliographic references:
Fontes, S. and Fontes AI (1994). Theoretical considerations on psychophysical laws. Rev. of Psychol. General and Application, 47 (4), 191-195. National University of Distance Education (UNED).
University of Barcelona (sf) Classical and contemporary psychophysics. (Online). Available at: http://www.ub.edu/pa1/node/113.
