<P> In linguistics, backchannels are listener responses in a primarily one - way communication . These can be both verbal and non-verbal in nature, and are frequently phatic expressions, primarily serving a social or meta - conversational purpose, rather than involving substantial two - way communication . </P> <P> The term "backchannel" was designed to imply that there are two channels of communication operating simultaneously during a conversation . The predominant channel is that of the speaker who directs primary speech flow . The secondary channel of communication (or backchannel) is that of the listener which functions to provide continuers or assessments, defining a listener's comprehension and / or interest . </P> <P> Due to research development in recent years, backchannel responses have been expanded to include sentence completions, requests for clarification, brief statements, and non-verbal responses and now fall into three categories: non-lexical, phrasal, and substantive . A non-lexical backchannel is a vocalized sound that has little or no referential meaning but still verbalizes the listener's attention . In English, sounds like "uh - huh" and "hmm" serve this role . Phrasal backchannels most commonly assess or acknowledge a speaker's communication with simple words or phrases (for example, "Really?" or "Wow!" in English). Substantive backchannels consist of more substantial turn - taking by the listener and usually manifest as asking for clarification or repetitions . </P> <P> The term was coined by Victor Yngve in 1970, in the following passage: "In fact, both the person who has the turn and his partner are simultaneously engaged in both speaking and listening . This is because of the existence of what I call the back channel, over which the person who has the turn receives short messages such as' yes' and' uh - huh' without relinquishing the turn ." </P>

Backchanneling cues such as yes and uh-huh come under which stage of listening