The historical roots of the theories of local signs and labelled lines

The theories of labelled lines and local signs are commonly invoked to explain numerous perceptual phenomena. These theories postulate that perceptual systems use information about which nerve cells or which information channels are activated by the stimulus. The origins of this idea in nineteenth century German psychophysics are traced. From Descartes's idea of a dualistic mind, Kant's idea of a mental ability to conceive space, Da Vinci's ideas of pictorial 'signs', and Müller's idea of 'specific nerve energies' to explain perceptual qualities, Steinbuch, Lotze, and others derived the conclusion that neural-level signs exist that signal stimulus location to the mind. Helmholtz, Hering, and others soon suggested variations on this basic idea. By the time of James the theory had changed yet again. It was revived elsewhere in the 1920s and again in the 1970s, although used implicitly by many workers in between and since. Against a modern metaphysical background, however, a distinction between labels (hardware) and signs (symbols) is the minimum step needed towards an appropriate and comprehensive explanation of perceptual behaviour and experience.