Story of Psychology - Morton Hunt [77]
At last he began spontaneously to improve and after a while could see without pain and talk to people. When he walked in the garden for the first time in many months, the flowers looked brighter, more intensely colored, and more beautiful than ever; he perceived an inner light in them, the significance of which he instantly grasped:
I had no doubt that I had discovered the soul of the flower, and thought in my strangely enchanted mood: this is the garden that lies behind the boards of this world. The whole earth and its very body is merely a fence around this garden for those who still wait on the outside.36
He soon wrote a book about the mental life of plants and for the rest of his many years sought to promote his panpsychist theory that consciousness coexists with matter throughout the world.
It was this mystical belief that led Fechner to his historic work in experimental psychology. Lying in bed on the morning of October 22, 1850, pondering how to prove to the mechanists that mind and body were two aspects of a fundamental unity, he had a flash of insight: If he could show a consistent mathematical relationship between the force of stimuli and the intensity of the sensations they produced, he would have shown the identity of body and mind.37
Or so it seemed to him; the logic of the reasoning may escape the nonmystic. But he had asked a valid and important question about the accuracy with which the mind perceives the outer world: Is there a consistent mathematical relationship between the magnitude of a stimulus and the magnitude of the sensation it creates? Intuitively, it might seem so: the brighter a light, the brighter it looks to us. But if you double the light, do you double the intensity of sensation? Or does some other, less verisimilar relationship prevail?
Fechner, trained in both physics and mathematics, sensed that as the intensity of a stimulus increased, it would require ever larger differences (in absolute terms) to produce increases of constant size in sensation. In mathematical terminology: Geometrical increases in the strength of the stimulus would produce arithmetical increases in the strength of the sensation. A contemporary illustration: In terms of energy delivered to the ear, an average clap of thunder is many times as powerful as ordinary conversation; in terms of decibels—a decibel is the smallest difference in loudness the human ear can recognize—it is only twice as loud.
To confirm his intuition experimentally, Fechner would have to solve a seemingly insoluble problem: He could easily measure stimulus intensity, but sensations are subjective and incapable of being measured. He reasoned, however, that though he could not observe and measure sensation directly, he could do so indirectly by using sensitivity as a guide. He could determine the smallest increase in stimulus strength at any level that would be just barely noticeable to the perceiver. Since “just barely noticeable” meant the same thing at any level, that would be a unit of measurement of sensation he could compare with the increase in stimulus necessary to produce that awareness.
Fechner later said that he did not get this idea from Weber, his former teacher, whose work on j.n.d.’s had been published a few years earlier. But he soon realized that he would be using and extending Weber’s Law. Weber had found that the ratio between two just noticeably different stimuli remains the same, whatever the magnitude of those stimuli; Fechner was saying that although the absolute difference between two stimuli increases as the magnitude of the stimuli does, the perceiver’s sensation of a just noticeable difference remains the same.
Imagine (Fechner later wrote) that you look at the sky through a tinted glass and pick out a cloud that is just noticeably different from the sky background. Now you use a much darker glass; the cloud does not vanish but is still just barely visible—because although the absolute levels of intensity are much lower through