"Machines take over functions of the central nervous system, and no longer, as in the past, merely those of muscles. And with this differentiation - and not with steam engines and railroads - a clear division occurs between matter and information, the real and the symbolic" (Kittler, GFT, 16).
The January 2002 issue of Artforum included the following letter to the editor and response: 
"Peter Plagens describes Ada’s Garden as having a green background. The background is dark gray. It is depressing to have my paintings reviewed by a critic who is inattentive or color blind."
--Alex Katz, New York
"English racing green" isn’t green as in Kelly, but rather almost black. And that’s the color I saw in the painting. But if Mr. Katz wants to swear that there’s absolutely no green paint mixed into his "dark gray," then I’ll concede that my perception was affected by a combination of gallery lighting and a little synaesthesia from the title, Ada’s Garden.
Derived from anaesthesia (loss of feeling or sensation), the term synaesthesia is formed by combining syn (with, together, similarity, alike) and aesthesia (to feel, perceive). Commonly defined as "A sensation in one part of the body produced by a stimulus applied to another part –or- Production, from a sense-impression of one kind, of an associated mental image of a sense-impression of another kind,"  synaesthesia results from the subject’s interaction with media and is not itself a medium. Rather, it is the product of a process of mediation. Taking the first definition literally, one could conclude that sexual arousal, as a sensation felt in one part of the body instigated through stimulus applied to another part of the body, is a kind of synaesthetic experience. When one becomes sexually aroused as a result of viewing a nude, through scents, tastes, or by touch -- which in the case of the kiss can involve both the tactile and taste –- sensation is transferred through the body from one part to another. The body, in this instance, serves as an enormous sensing or mediating organ. More common, however, is the second definition of the term in which synaesthesia is used to describe the human mind’s ability to confuse "sense-impressions." For example, Plagens’ use of the active verb "to affect" points to how the word garden acted upon the critic’s visual capacities, hence causing him to see green where there was none. Although this form of synaesthesia is most commonly associated with "colored-hearing" and as such the production of visual images resulting from aural stimulus, Plagens’ invocation of the term in describing how text colored the critic’s vision of a painting indicates its potential application to multiple and mixed media. In other words, one can experience synaesthesia in reaction to a variety of media.
Given that the term can be defined both as a physical sensation felt in and through the body as well as a "sense-impression" mistranslated by the mind in which one sense is replaced by another, then the question is not how synaesthsia acts as medium, but rather which media elicit a synaesthetic response -- whether bodily or psychological -- in the subject and which subjects are prone to synaesthesia. While the term synesthétique did not enter the French dictionary until 1872, the synaesthetic had been invoked as early as 1690 when John Locke, in his "Essay Concerning Human Understanding," tells of a blind man who when asked to describe the color scarlet, responded by stating that "it [scarlet] was like the sound of a trumpet."  It was in the 19th-century, however, that cases of synaesthesia began to be documented, leading to formal studies of the "condition" by both neurologists and experimental psychologists. Studied to this day as a medical condition, a distinction need be made between synaesthesia that results from a developmental or neurologically dysfunctional process of the brain and what Baron-Cohen and Harrison consider pseudosynaesthesia, which is invoked by the subject as metaphor or is the effect of drug use. 
Through extensive neurological testing, it can be determined that one’s brain is able to involuntarily associate color with sound. Cases of such scientifically legitimate synaesthesia, however, are exceedingly rare and the precise neurological function of the brain responsible for the multiple sensations remains unknown. Most often, the subject (like Plagens) voluntarily makes metaphorical associations between sound and color. French phenomonologist M. Merleau-Ponty contends, however, that "Synaesthetic perception is the rule, and we are unaware of it only because scientific knowledge shifts the center of gravity of experience, so that we have unlearned how to see, hear, and generally speaking feel."  Regardless of this debate concerning science and the subject’s alienation from his body, it is pseudosynaesthesia that has been employed by writers, composers, and visual artists who since the late 19th-century have manipulated their media with hopes of (re)creating a "legitimate" or clinical synaesthetic response in the subject.
Of numerous literary examples, the Symbolist poet Charles Baudelaire often invoked "a unity of sensation" in his texts and Harrison and Barron-Cohen believe this to reflect the poet’s belief that there existed a "natural correspondence between the senses."  For example, In Correspondences, he includes the lines:
Like long echoes that mingle from far away
In profound and shadowy unity
Vast like the night and like clarity
Scents, sounds and colours respond to one another
This example, however, is less evocative of the concept than Plagens’ simple transfer of color onto text. In fact, Harrison and Barron-Cohen contend that it is much more common for single words or even fragments of words (sounds) to bring about a color association in the subject. As such, in Correspondences Baudelaire represents a synaesthetic sensibility rather than a vehicle for synaesthesia itself.
In music, Alexander Scriabin is most closely associated with the concept. In his orchestration of Prometheus, the composer included a "color organ." Each pitch of the keyboard associated with a different color, the instrument produced color rather than sound when played. Scriabin claimed, as did many other composers and artists working in the early 20th-century, that his experience with music was one of synaesthesia. By adding a visual element to an otherwise aural medium in Prometheus, he attempts realize externally, his internal associations of color and sound.
In the visual arts, Wassily Kandinsky (a contemporary of Scriabin) is most noted for aspiring to produce synaesthetic painting. Like Scriabin, he too believed that his experience of color was one of sound and vibration. As elaborated in his Concerning the Spiritual in Art, the artist believed that vibrations of color and form could be collected into a universal language (a type of semiotic) that the viewing subject could instinctively comprehend. Although, much has been written on his mission’s shortcomings, his desire was to replicate his experience of the synaesthetic through the medium of painting.
It is, however, Richard Wagner who in the late 19th-century famously desired to create what we would consider a multi-media experience today. In his operas, Wagner sought to unite the visual, the aural, and narrative text into a single artistic unity or gesamtkunstwerk. The viewing subject was to be enveloped by sound, vision, and text, creating an experience not in which one sense was replaced by another, but rater an experience in which the senses intermingled and perhaps ultimately became one. This transcendental form of synaesthesia is perhaps most akin to what one experiences today in our world of multi-media(s), like film and the internet, in which media are constantly intertwined.
Instances in which media elicit the sensation of smell, touch, or taste through an unrelated sense are relatively rare. As is evident in the above examples in which a the visual and the aural are synaesthetically interchanged, the predominance of synaesthetic linkages between these two senses may be due to the audio-visual nature of media itself.
Jeffrey T Saletnik
Department of Art History