The role of the homunculus

Ideas about perception have changed a great deal over the past half century. Before the discovery of maps of sensory surfaces in the cerebral cortex the consensus view was that perception involved “mind-stuff”, and because mind-stuff was not matter the greatest care was required in using crude, essentially materialistic, scientific methods and concepts to investigate and explain phenomena in which it had a hand. One approach was to reduce the role of this mind-stuff to a minimum by designing experiments so that the mind was used simply as a null-detector, analogous to a sensitive galvanometer in a Wheatstone bridge, which had to do no more than detect the identity or non-identity of two percepts. Those who followed this approach might be termed the hard-psychophysics school – exemplified by people such as Helmholtz, Stiles, Hecht and Rushton – and it had some brilliant successes in explaining the properties of sensation: for instance the trichromatic theory; the relation between the quality of the retinal image and visual acuity; and the relation between sensitivity and the absorption of quanta in photo-sensitive pigments. But it left the mystery of the mind-stuff untouched.

Others attempted to discover the properties of the mind-stuff by defining the physical stimuli required to elicit its verbally recognizable states – a soft-psychophysics approach that could be said to characterize the work of the Gestalt school and, for example, Hering, Gibson, and Hurvich and Jameson.