Eye music (often referred to in English by its exact German translation Augenmusik) describes graphical features of scores which when performed are unnoticeable by the listener. Difficulties in defining eye music By simple definition eye music is when the graphic notation of music is altered in some meaningful way visible to the performers. Often the changed "meaning" of the altered notation is enhanced by the music having compositional elements of melody and form such as word painting and canon. Moreover, the concept is demonstrated by sometimes differing perceptions of composer, performer, and listener. Eye music and puzzle-solving The difficulty in definition is also apparent with border-line cryptographic contrapuntal works such as puzzle canons, which appear in the score entirely as a bare line of notes with clefs, rests, time signatures, or key signatures as clues to reveal multiple lines of music in canon. (Closer to true cryptographic works would be those with soggetto cavato, where letters are embedded in the work using their solfège names.) As an example, a puzzle canon might be notated as one line of music with two key signatures and clefs, where the worked-out result will be a two-voice canon with one voice the retrograde (reverse) of the other. In itself the score with the clues alone is not eye music. But represent the same work "graphically spelled out," however, say with a drawing of the clued score facing a mirror, and the score/drawing becomes eye music. The type of puzzle canon is also a factor. A four-voiced circular canon, when notated as a puzzle canon, may remain an un-worked-out single line of notes, and be inadmissible as eye music. When that single line of notes is inscribed in a graphical shape it becomes eye music, even if the contrapuntal puzzle remains unsolved. An even finer use of graphical conceit is when the canon does not have any musical way to end, and are in a sense "infinite"—classically referred to as canon perpetuus, more commonly as "circular canons," and even more commonly as "rounds." When an infinite (circular) canon is inscribed in a circle, and the circle itself is a clue that means "play me as a round," a different type of eye music entails. Eye music for the performer Another class of eye music is when the score is purposely made difficult for the performer. For example, in Benedetto Marcello's cantata Stravaganze d’amore, the continuo