ABSTRACT
Hermann von Helmholtz contributed two major works to the theory of sensation and perception in the nineteenth century. In his Handbook of Human Physiology, Helmholtz's mentor Johannes Muller defends the vitalist position: that the body must have an organizing force beyond the mechanical forces at work in processes like metabolism. Muller draws his inspiration from Kant, but marshals evidence from Ernst Stahl's and Georges Cuvier's naturalist studies. Sensation alone, as response to a stimulus, never adds up to perception or representation of an object. Helmholtz adapted his characteristic physiological stance on sensation from Muller. A stereoscope separates the visual field of each eye, and presents each eye with a separate picture, which the brain then fuses into a single image only if the pictures are kept at the right distance and angle of sight. Helmholtz argues that inferences from sensation to objective representation, in many cases, are inductive "unconscious inferences".
