The Collaborative International Dictionary of English v.0.48:

Autophony \Au*toph"o*ny\, n. [Auto- + Gr. ? a sound.] (Med.)
   An auscultatory process, which consists in noting the tone of
   the observer's own voice, while he speaks, holding his head
   close to the patient's chest. --Dunglison.
   [1913 Webster]