"Our laboratory here at UC San Diego specifically examines
grapheme-color synesthesia, in which people see colors when looking at
letters and numbers, and what we refer to "sequence forms" in which
numbers (and other sequences, like days of the week and months of the
year) are experienced as having a spatial form. Sometimes these number
sequence forms are colored, sometimes not.
We are continuing to explore the experiences of synesthetes, and the
neural basis of synesthesia through a combination of psychophysical
experiments and functional magnetic resonance imaging (fMRI) in
collaboration with Geoffrey Boynton at the Salk Institute.
If you experience any form of synesthesia, and would be interested in
participating in our research, please feel free to contact us, either
via e-mail or via telephone.
Edward M. Hubbard
Center for Brain and Cognition
University of California, San Diego
9500 Gilman Dr.
La Jolla, CA 92037-1300
(SOURCE: http://psy.ucsd.edu/~edhubbard/ - the reason that I haven't
posted it as an answer, is that Hubbard seems to be currently in
France, and I am not sure if the lab is still active. If it is, please
let me know, so I can post an official answer).