ABSTRACT
This chapter focuses on visual psychophysics in the nineteenth century. In his section on Joseph-Remi-Leopold Delboeuf in his The Case for Psychophysics, Gustav Theodor Fechner discussed the Etude, another book by Delboeuf, and the article on Ewald Hering versus Fechner. While preparing his psychology course, he read the first edition of W. Wundt’s Lectures on Human and Animal Psychology, from which he learned about Fechner’s Elemente der Psychophysik. A decade earlier, factors indigenous to receptor physiology were invoked when von Helmholtz described Fechner’s Law during Helmholtz’s discussion of intensity of sensations of light. In his reply to Plateau, Fechner himself argued that his own derivation of his logarithmic law could be modified at its very outset in such a way as to yield a power law. Fechner wrote at considerable length about the need to obtain more evidence as to whether Weber’s Law could always be applied to perception of small differences in stimulus intensity when the stimuli were visual.
