Sunday, February 12, 2023


The discipline of psychology was going through rapid changes in the mid-nineteenth century. The rise of experimental physiology had a strong influence on psychology. Extensive research in experimental physiology, in those times, played a significant role in the experimental method being introduced into psychology. One of the main reasons behind this was the emergence of the discipline of psychophysics.

Psychophysics emphasizes the subjective experiences in the study of the relationship between physical stimuli and sensations. It examines sensations from many different perspectives. Psychophysics considers sensations with respect to the mind-body problem. It is a discipline that comes within physiology, physics, and natural philosophy.

The major proponent of psychophysics is the German physiologist, physicist, philosopher, and experimental ethicist, Gustav Theodor Fechner. Fechner had started working as a professor of physics at Leipzig in 1833. In 1840, he suffered a nervous breakdown. He became a recluse and began to experience severe depression. It was this phase that made him interested in philosophy. His interest in philosophy made him interested in the mind-body relationship.

Fechner wanted to solve the mind and body problem in a scientific manner. He disagreed with the idea of Descartes that mind and body are two separate entities (dualism). He, instead, agreed with the idea of Spinoza that the mind and body are two aspects of the same entity, that is, double aspectism. Fechner wanted to prove the idea of double aspectism, instead of only speculating about it.

Gustav Theodor Fechner

In the year 1950, Fechner came up with a way to prove Spinoza’s idea of mind and body. He realized that as a physical stimulus is systematically varied, the changes in sensation reported by an individual (subject) can be measured. Accordingly, Fechner felt that a systematic relationship between bodily and mental experiences can be demonstrated. The testing of these ideas led Fechner to create the discipline called psychophysics. Psychophysics is the scientific study of the relationship between physical stimuli and the sensations and perceptions that they evoke.

To measure sensations, Fechner proposed the idea of absolute threshold. Absolute threshold is the lowest intensity at which a stimulus can be detected. Thus, absolute threshold is the intensity of stimulus at or above which a stimulus is detected. If the intensity of the stimulus is below the absolute threshold then it is detected in the unconscious. 

Fechner felt that the absolute threshold is only one measure of sensations and thus found its usage to be limited. He was looking to have a continuous scale that indicated how the sensations that are above the absolute threshold vary with respect to stimulation. He then proposed the idea of differential threshold - the least amount of change in magnitude of a stimulus required to detect a difference (just-noticeable difference, JND).

The idea of just-noticeable difference was first proposed by the German physician and experimental physiologist Ernst Heinrich Weber. Weber did this by asking subjects in his experiments to compare weights and report whether one felt heavier than the other. Weber also introduced the idea of the two-point threshold - the point at which two separate stimulations can be distinguished.

Ernst Heinrich Weber

Weber’s research on thresholds introduced a method for measuring the relationship between body and mind - the relationship between physical stimulus and the sensation associated with it. This was seen as a major breakthrough. However, Weber was interested in physiological processes and did not see the importance of his findings in psychology. It was Fechner who had attended Weber’s lectures on physiology realized the importance of these findings and used it to develop his discipline of psychophysics. Due to this, even though Fechner began the discipline of psychophysics, it is Weber who is often considered to be the first psychophysicist.

To further explore the mind-body relationship, Fechner developed three methods of psychophysics. The first is the method of limits or the method of just-noticeable differences, in which the subject is asked to detect or respond to minimal change in stimulus values. The second is the method of constant stimuli or the method of right and wrong cases, in which the subject has to judge repeatedly which of the two stimuli is the more intense. And, the third is the method of adjustment or the method of average error, in which subjects are asked to adjust stimuli until they are equal.

Psychophysics gave a major thrust to the beginning of modern psychology. Psychophysics demonstrated that sensations and mental experiences can be quantitatively measured. This was a landmark discovery, as a number of earlier scholars had raised doubts regarding this. They were all proved to be wrong. 

The idea of the quantitative measurement of experience turned out to be highly significant for the beginning of modern psychology. Wilhelm Wundt, considered to be the founder of modern psychology, had envisioned the discipline of psychology to be the scientific investigation of consciousness. The quantitative measurement of sensations helped Wundt in achieving his vision.

Further, Fechner’s book The Elements of Psychophysics, which was published in 1860, was a significant contribution to scientific psychology. This book is considered to be the beginning of experimental psychology. Wundt himself felt that Fechner should be credited for the beginning of experimental psychology. 

Edward Titchener, the student of Wundt and the founder of structuralism, the school that firmly established psychology as a scientific discipline and strongly emphasized the experimental method, considered Fechner to be the founder of experimental psychology. The introduction of the experimental method in psychology was highly significant in making it an independent, scientific discipline. In this regard, the contribution of psychophysics is paramount.   

The methods of psychophysics proposed by Fechner were also a major contribution to the beginning of modern psychology. These methods were used by Wundt, and later by Titchener, in order to understand consciousness in their laboratory. The methods of psychophysics have thus, contributed immensely to modern psychology. For any discipline to be scientific, it needs to have precise techniques of measurement. The methods of psychophysics are exactly that and helped Wundt to establish his scientific psychology. These methods are extensively used in psychology even today.

Wilhelm Wundt was highly instrumental in introducing the experimental method to the discipline of psychology, which is often dubbed the beginning of modern psychology. Wundt, however, was provided with a platform that enabled him to bring about such changes. One of the most significant of such platforms was psychophysics, therefore, making it a major precursor to modern psychology. 

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