Marc Leman notes (Lemon 1996), "experiments with Shepard-tones have
contributed to a decline of the phenomenological approach to pitch perception."
Indeed, as Lemon further points out, only when referenced against such
an approach can we call Shepard tones "paradoxical" or "illusory."
In the next chapter, we study further the effect of shepard tones, taking a look at
Diana Deutsch's investigation of the so-called "tritone paradox."