Daniel Tammet has memorized Pi to the 22,514th digit. He speaks ten different languages, including one of his own invention, and he can multiply enormous sums in his head within a matter of seconds. However, he is unable to hold down a standard 9-to-5 job, in part due to his obsessive adherence to ritual, down to the precise times he has his tea every day.
I don't know about you, but to me Wednesday is sun-shiney yellow. Tuesday is hunter green, Thursday purple-ish blue and Friday a deep red. Monday is white, a blank slate and a chance for a new week, whereas Saturday is sparkly black. Sunday is gray, the depressing slouch towards the beginning of the work-week, but also a convenient mix of Saturday and Monday.
This color-word association is not a figment of my imagination or an indication that I'm going crazy, but is instead a recognized neuropsychological phenomenon called synesthesia. Synesthesia can be thought of as a crossing of the senses, where one perceptual experience simultaneously expresses another. It is estimated to occur in some form in roughly 20% of the population, with color-grapheme being the most common (1). Here, letters or numbers are experienced as taking on unique and varying shades of color. Apparently the experience that I have is also quite common, wherein units of time - such as days of the week - are also expressed in color. There are up to 60 different forms of synesthesia, including sound-color, grapheme-shape and, my personal favorite, word-taste. In this last one, words or names are experienced as different flavors in the individual's mouth. Reported palates range from buttered toast to berries and everything in between. Think of it as chewing a different flavored jellybean for every person that you know.
Synesthesia is loosely defined as a merging of the senses, the notion that one sensation can trigger a separate perception. This is most commonly manifested as individuals who perceive color with letters or numbers (known as grapheme-color synesthesia), however other variants include experiencing taste with words, texture with taste, or color with music. It is important to note that the secondary, or concurrent, sensation does not replace the primary, or inducer, perception, but is instead experienced in addition to it. There are currently 61 known variants of synesthesia, spanning the perceptual spectrum of color, taste, sound, touch, and even higher level cognitive conceptions, such as language. At first glance, these phenomena seem quite unique and binary (after all, you either taste rectangle or you don't), and the prevalence of synesthesia was originally thought to be roughly 1 in 1000. However, new research on sensory integration has revealed that varieties of synesthesia may be much more common than originally thought, and that there may be a sliding scale in the amount of sensory cross-talk among individuals.