Number-form synesthetes visualize numbers in a three dimensional or spatial way. Richard Cytowic (2009) relates the experience of one woman, “…the professor handed her a length of stiff wire and asked her to indicate where along it the figures were located. He then watched as, without the least hesitation or surprise, ‘she took the wire and bent it here and there in three dimensions until it looked like a tortured thing. A number of times, she returned to the previously made bends, correcting the angles precisely” (p. 2). For another synesthete, “the numbers progressed around an imaginary clock face in traditional fashion until 10 o’clock, then began to spiral backwards onto a second clock face above and behind the first up to number 20, with successive loops of the helix fading into the distance for each decade beyond that” (Robertson & Sagiv, 2005, p. 43).
Cytowic, R. and Eagleman, D.M. (2009). Wednesday is indigo blue : Discovering the brain of synesthesia. Cambridge, MA: MIT Press.
Robertson, L. C., & Sagiv, N. (2005). Synesthesia: Perspectives from cognitive neuroscience. New York, NY: Oxford University Press.