How rare is synesthesia?

Question

I visited a neuropsychologist recently who told me I have Synesthesia. I never really knew what it was, but it's fascinating and I can't believe it isn't the norm among people. For me, certain numbers just have had personalities (I also have this weird object/perception ability... but I'm not sure if that's Synesthesia).

For some reason, the more difficulty I had with the number, the more complex personality it had. For instance, I had a lot of trouble with odd numbers, and larger numbers. Therefore, 1 and 2 do not have personalities. On the contrary, 7 and 9 are the most developed personalities (7 being a male loner who lives in his mom's basement, and 9 being a mean female who is very cruel to 7). I'm not sure if anyone knows what I'm talking about...

How rare is this condition?

Answer 1

From Hubbard & Ramachandran (2005):

[...] the estimated prevalence of synesthesia has varied dramatically, between as many as 1 in 20 (Galton, 1883) and as few as 1 in 25,000 (Cytowic, 1989). The most widely cited study to date suggests that synesthesia occurs in at least 1 in 2000 people (Baron-Cohen et al., 1996), although this is now generally regarded as an underestimate. Our own informal samples have suggested that the prevalence of grapheme-color synesthesia might be between 1 in 200 (Ramachandran and Hubbard, 2001b) and 1 in 100 (Mulvenna et al., 2004). Subsequent large-scale studies have suggested that the prevalence of synesthesia might be as high as 1 in 20 across all forms and 1 in 100 for grapheme-color synesthesia (J. Simner, personal communication). This high prevalence argues against the notion that synesthesia is merely a “benign cognitive variant” (see Ward and Mattingley, 2005) and instead suggests that it is a widespread phenomenon that may provide novel insights into the neural basis of the mind (Ramachandran and Hubbard, 2001b).

  References

Hubbard, E. M., & Ramachandran, V. S. (2005). Neurocognitive mechanisms of synesthesia. Neuron, 48(3), 509.

Answer 2

The wikipedia Article on Synesthesia cites some prevalence studies

Random population studies ... determined that 1 in 23 individuals have some kind of synesthesia, while 1 in 90 have colored graphemes (Simmer et al 2006). Colored days of the week and colored graphemes are the most common types(Simmer et al 2006; Campen, 1999).

References

• Simner J, Mulvenna C, Sagiv N, et al. (2006). "Synaesthesia: the prevalence of atypical cross-modal experiences". Perception 35 (8): 1024–33. doi:10.1068/p5469. PMID 17076063.
• Campen C (1999). "Artistic and psychological experiments with synesthesia". Leonardo 32 (1): 9–14. doi:10.1162/002409499552948.