Synesthesia

syn·es·the·sia:     si-nəs-ˈthē-zh(ē-)ə

1.  the production of a sense impression relating to one sense or part of the body by stimulation of another sense or part of the body.

2.  a subjective sensation or image of a sense (as of color) other than the one (as of sound) being stimulated

     i.e., hearing colors; seeing music; tasting rhythm