An experiment compared the ability of classical pianists to sing, during keyboard performance, the right- and the left-hand part of the score being played. Upon instructions requiring them to "sing" one or the other voice of the score, the subjects spontaneously chose to sing and name the notes simultaneously, in keeping with the French traditional way of reading music, thus producing a two- dimensional tonal and verbal vocal act in response to each visual stimulus. Singing the right-hand part of the music, whether in unison with or in place of the right hand, while concurrently playing the left-hand part was judged easy by all subjects, and performance, typically, was correct in all respects. The other task, consisting of singing the left-hand part of the music, was judged more difficult by all subjects, and performance, more often than not, was poor. Careful inspection of the many errors that were recorded in the latter task revealed a few clear-cut regularities. Failures were vocal, but not manual. More specifically, vocal failures took place on the tonal dimension of the vocal response, but not on its verbal dimension: The song, but not the naming of the notes, was prone to fail, with either a loss of the pitch, or a systematic trend toward singing unduly—albeit accurately—the notes of the right-hand part. A number of subjects were found to display this intriguing tonal/verbal dissociation—naming a note at a pitch corresponding to another note—in a continuous regime. It is emphasized that this phenomenon amounts to the spontaneous production of musical events that belong to the Stroop category.