The long a of the English alphabet...has for me the tint of weathered wood, but a French a evokes polished ebony. This black group also includes hard g (vulcanized rubber) and r (a sooty rag being ripped). Oatmeal n , noodle-limp l , and the ivory backed hand mirror of o take care of the whites.
--Nabokov, Speak Memory 1966
Synaesthesia challenges the classic view of perception, first formulated by Aristotle, that each of the five senses--sight, sound, hearing, taste, and touch--has a distinct and proper sphere of activity (Gage 348). (See Ear, Eye and Gaze, and Senses) Derived from the Greek syn (meaning union) and aesthesis (sensation), the term synaesthesia is used to describe the "production, from a sense impression of one kind, of an associated mental image of a sense impression of another kind" as well as "the production of a synaesthetic effect" through the "use of metaphor" (OED). The first definition refers primarily to a neuropsychological phenomenon, and is used to describe the experiences of those who hear colors, taste shapes, or otherwise demonstrate the capacity to experience two sensations simultaneously as the result of exposure to a single stimulus (Gage 348). The latter definition describes attempts made to simulate this experience through the use of aesthetic techniques, such as metaphor. Both types of synaesthetic experience raise questions, articulated in W.J.T. Mitchell's essay "Word and Image," about the 'natural' semiotic and aesthetic order...The nature of the senses, the media, the forms of art is put into question: natural for whom? since when? and why?" The term synaesthesia works both to describe the abnormal perceptions of a small group of people, and to reveal what 'normal' perceptions are thought to be.
Testing the limits of 'normal' perception with techniques such as metaphor and symbolism, synaesthesia became a preoccupation of many in the late nineteenth century. The Symbolist poet Arthur Rimbaud is often cited as having demonstrated synaesthetic perception in his sonnet, Les Voyelles (1871). In the opening line of the sonnet, "A noir, E blanc, I rouge, U vert, O bleu: voyelles", Rimbaud assigns color values to different vowels. In doing so, he seems to go a step beyond the experiments in synaesthetic technique carried out by his predecessor Charles Baudelaire, who created elaborate lists of sensory "correspondences". Explaining Baudelaire's system of correspondences, A.G. Lehmann writes:
On Baudelaire's theory, every colour, sound, odour, conceptualized emotion (love, hate, cf affect), every visual image, even if complex (a ship, a carcass), is in some way bound up with an equivalent in each of the other fields: one only, we may infer. (207)
While the system works as synaesthesia on the level of metaphor, it is not necessarily a manifestation of the rare neuropsychological disorder. Baudelaire's system depends on associations evoked by the content of a word. For example, in the poem Correspondences, he writes, "Il est des parfums frais comme des chairs d'enfants": there are perfumes as fresh as children's flesh (quoted in Baron-Cohen 99). On the other hand, because Rimbaud sensory connections are revealed in the experience of saying a word, he comes much closer to expressing or simulating the synaesthete's experience. In Les Voyelles , the sounds made in the pronunciation of the each of the vowels in seems to evoke the color it is paired with (Gage 349). Despite their different approaches to synaesthetic experience, both Baudelaire and Rimbaud seized upon it as a means of innovation. Both wished to change fundamentally the way that people read, understood, and experienced poetry.
The line between synaesthesia as a physiological phenomenon (first definition) and synaesthesia as metaphor (second definition) is blurry. Telling the aesthete from the synaesthe has become a favorite occupation of those who have written about synaesthesia in recent years. In an article on synaesthesia and aesthetics, Jörg Jewanski reveals the problems of this practice: "The fundamental difficulty in assessing the artistic significance of synaesthesia is that in the case of many musicians and artists it is impossible to be sure whether they are experiencing synaesthesia, have a heightened sensitivity to interdisciplinary associations and/or are seeking new ways of expressing themselves by deliberately blurring the frontiers between the arts. However, from an aesthetic perspective, the practice of differentiating between 'true' synaesthetes and mere imitators is less important than understanding how and why artists turn to synaesthesia in an effort to "deliberately blur" the boundaries between "normal" and "abnormal" perception."
In order to richly describe the ways in which artists like Rimbaud expressed or simulated synaesthetic experience, it is useful to determine what is unusual about the ways in which officially diagnosed synaesthetes perceive the world around them. Having developed more sophisticated techniques of monitoring activity in different parts of the brain, neurologists have been able to identify "objective physiological changes" that occur during synaesthetic perception (Cytowic 285). Neuropsychologists such as Richard Cytowic have developed tests, based on these observations, which can be used to determine whether or not someone is a true synaesthete. Cytowic emphasizes the involuntary nature of synaesthetic perception. In addition, he argues, synaesthesia can be differentiated from imagination. When a person imagines something, it is said that he perceives something in his "mind's eye". For the synaesthete, on the other hand, additional sense perception often is experienced outside of the body (Cytowic 1). Vladimir Nabokov illustrates this property of synaesthesia in a description of his experience of colored hearing (the most commonly reported type of synaesthetic experience), taken from his autobiography, Speak, Memory:
I present a fine case of coloured hearing. Perhaps 'hearing' is not quite accurate, since the color sensation seems to be produced by the very act of my orally forming a given letter while I imagine its outline (quoted in Harrison 131).
Regardless of whether Nabokov was truly a synaesthete in the physiological sense of the word, synaesthetics played a vital role in his creative processes. Many other artists, writers, and musicians also involved synaesthetic phenomena in the process of their compositions, typically with the aim of broadening the sensory experiences of those who come into contact with their work.
While some artists make a space in their work for synaesthetic perception through the use of sensory fusion, others elicit the same effect through abstraction. The Russian composer Aleksandr Scriabin falls into the former camp. In 1911, he composed Prometheus, The Poem of Fire for an orchestra, piano, organ, choir, and a "light organ" or "clavier à lumieres". The light organ was a silent instrument that "could control the play of colored light in the form of beams, clouds, and so forth, flooding the concert hall and culminating in a white light so strong as to be 'painful to the eyes'." He also planned a piece called Mysterium, which was to include dance, and odors, in addition to music and colored lights. As the title suggests, this work was to move the audience beyond the realm of normal perception to a "supreme, final ecstasy" achieved through the fusion of sensory experiences (quoted in Cytowic 271).
Wassily Kandinsky hoped to achieve the same end through different means. For those seeking the spiritual in his abstract compositions, the possibility resides in the free interplay of color and music. According to Harrison, Kandinsky's "intention was for his work to possess the quality of evoking sounds (klangen) in those who viewed his canvases"(127). Of course, whatever Kandinsky's intensions might have been, it is difficult to evaluate the synaesthetic effect his work has on the viewer. While a "sender" like Scriabar or Kandinsky might infuse their work with real or simulated synaesthetic experience, this does not guarantee that their compositions are perceived as synaesthetic by a "receiver".
Both Scriabin and Kandinsky tested the limits of their media. Scriabin asserted that color, light, and perfumes are tools external to the medium of music that should be at the disposal of the composer in the achievement of a total effect. Kandinsky, on the other hand, uncovered new possibilities within the medium of painting, questioning what it is and showing what it can be. In blurring the boundaries between arts, and destabilizing our notion of what a medium must be, Scriabin and Kandinsky raise questions about the way art--and more broadly, everything in the world around us--should be perceived. What happens when, in Baudelaire's words, the senses become "deranged", when they cannot be classified as acting within distinct spheres of activity? Synaesthesia forces us to question our assumptions about the relationship between perception and reality.