Short, Williams, and Christie (1976) describes social presence
theory for analyzing mediated communication. Main point: [p. 65]
"We hypothesize that communications media vary in their degree of
Social Presence, and that these variations are important in
determining the way individuals interact."
Short (1974) compared FTF, sound only, and CCTV communication to
test social presence hypothesis about persuasion.
Johansen (1977) uses social presence model to examine social
aspects of teleconferencing.