A Survey of Listener Behavior and Listener Models for Embodied Conversational Agents - Coverbal Synchrony in Human-Machine Interaction - page 245

the typical dynamics that people apply. These studies have been
conducted by Yngve (1970), Allwood et al. (1993), Poggi (2007), Welji
and Duncan (2004), Clark and Schaefer (1989), Schegloff and Sacks
(1982) and many more. One of the first studies about the expressive
behaviors shown by people engaged in an interaction has been
presented by Yngve (1970). His work focused mainly on those signals
used to manage turn-change, both by the speaker and the listener. To
describe this type of signals, Yngve introduced the term “backchannel”.
In this conception, backchannels are seen as non-intrusive acoustic and
non-verbal signals provided during the speaker's turn. Backchannels
are used to set the common ground without bringing much new
information.
Allwood et al. (1993) extended Yngve's theory. They chose the term
of feedback (originally introduced by Wiener (1948)) to encompass a
wider set of verbal and non-verbal signals that the listener can provide.
Feedbacks include not only non-intrusive acoustic and gestural signals,
but also single words or short phrases like “I see”, “Oh, that's great!”
that can need a full speaking turn to be expressed. In particular,
Allwood et al. analyzed the linguistic feedbacks from a semantic and
pragmatic point of view, considering them as mechanisms which allow
interlocutors to exchange information about four basic communicative
functions (Allwood et al., 1993):
￿ Contact : the interlocutor wants to and can continue the interaction,
￿ Perception : the interlocutor is willing and able to perceive the
message,
￿ Understanding : the interlocutor is willing and able to understand
the message,
￿ Attitude : the interlocutor wants to and can show her/his attitudinal
reactions to the communicated content, that is if she/he believes
or disbelieves, likes or not, accepts or refuses what the speaker
is saying.
Within their studies, Allwood and colleagues showed that
feedback behavior can convey more than one communicative
function at a time, for example an interlocutor can show, through
a feedback signal, that she/he is both understanding and
agreeing.
Through feedback signals, a listener can transmit both positive
and negative information (Poggi, 2007). A speaker does not need to
know only when the listener can perceive her/his words or understand
the content of her/his speech, but she/he needs also to know when
the perception decreases and when what she/he is saying is not