Synesthesia is a rare and interesting neurological phenomenon in which one sensory modality crosses over into another. Synesthetes therefore may see sounds, or taste colors. Abstract concepts may also evoke sensory experiences. In color-graphemic synesthesia letters or numbers evoke the perception of a specific color (for each individual the same number will always evoke the same color). In ordinal linguistic personifcation, days of the week or months of the year convey a specific personality. Other forms of synesthesia involve spacial relationships and size. Over 60 forms of synesthesia have been reported.
What is happening inside the brain in synesthetes is currently under study, but early evidence suggests that their brains are hardwired for the experience - literally there is a cross-wiring where one type of sensation or information processing leaks over into another.
A recently identified form a synesthesia is visual motion to sound synesthesia - people can hear visual motion or flickering images. While the overall prevalence of synesthesia is estimated at less than 1%, visual sound synasthesia may be more common. On a personal note, I have experienced this myself on several occasions when I was profoundly sleep deprived. Every time I blinked my eyes or scanned my eyes across different levels of lighting I would hear a distinct “whooshing” sound.
Charles Spence, a professor of experimental psychology, performs crossmodal research at Oxford University. He is looking at the effects of processing multiple sensory modalities simultaneously in the normal population - and he thinks that to a certain degree we are all synasthetes. On his website he writes:
Synaesthesia is a rare condition in which people report, for example, ’seeing’ a colour when they hear certain words, like the days of the week, or numbers. Everyday language also uses cross-modal correspondences to describe a variety of sensory experiences - tastes can be ’sharp’ and colours can be ‘loud’, for example. But can such synaesthetic correspondences be demonstrated in normal individuals for simple stimuli, such as brightness, size, colour, motion etc. This project investigates a number of questions in this line.
He explores things like, for instance, what name people think fits an abstract visual image. For example, which of these two shapes do you think is called “bouba” and which is called “kiki?”Most people will say the purple shape is bouba and the orange shape kiki. Why?
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