A developmental theory of synaesthesia, with long historical roots: a comment on Hochel & Milan

The recent surge of scientific investigation into synaesthesia, ably reviewed by Hochel and Milan (2008), is representative of an increasing recognition that our various sensory modalities are intimately interconnected rather than separate. The origin of these interconnections is the subject of an intriguing theory by Maurer and Maurer (1988). They suggest that all of us begin life as synaesthetes, with subsequent neural development reducing the connections among the senses. We present some historical roots of the idea that human life begins with the senses intertwined. The influential 18th-century philosopher Jean-Jacques Rousseau described an early theory of child development in his book Emile (1762), hypothesizing that if "a child had at its birth the stature and strength of a man ... all his sensations would be united in one place, they would exist only in the common 'sensorium'." A half-century later, a young Mary Shelley (1818) brought this idea into popular culture with the Frankenstein creature's recollection of his early experience: "A strange multiplicity of sensations seized me, and I saw, felt, heard, and smelt, at the same time; and it was, indeed, a long time before I learned to distinguish between the operations of my various senses." William James in The Principles of Psychology (1890) expressed a similar idea. In this context, the assumption of many 20th-century scientists that the senses were largely separate appears to be an historical aberration.