Speech does not require visual presence, even before telephones:
The phylogenetic choice of a particular acoustic material, the sound of the human voice, for the signifiers of human language [was probably chosen because] phonic commication is not interrupted by darkness or by night. You can speak to someone who is in back of you, or who is behind something, or whose location is unknown. The relatively weak relation to space provides multiple advantages the human race would not have benefitted from had a visual language been chosen.
--Christian Metz, "'Off-screen Sound' in the Cinema" (1980) in Film Theory and Criticism, eds. Gerald Mast, Marshall Cohen, and L. Braudy (Oxford UP, 1992), 315.
Last updated: 20 July 2002