“…Back-channel utterances are brief, often non-lexical expressions (e.g., uh-huh, mm-hmm) that implicitly communicate to a conversational partner that a listener is paying attention, interested, and would like the speaker to continue (Duncan, 1975; Peterson et al, 1999). Also referred to as “response tokens” (Gardner, 2001; McCarthy, 2003) or “facilitators” (Hershkowitz, 2002), back-channel utterances are prevalent in everyday conversations and have been found to be beneficial in a range of contexts, including interpersonal communication, education, and linguistics (Duncan, 1975; Krauss, Garlock, Bricker, & McMahon, 1977; Myers & Macnaghten, 1999; Roger & Schumacher, 1983; Tolins & Tree, 2014; Wannaruk, 1997). For instance, in classrooms, children produce longer responses when teachers include back-channel utterances that acknowledge what children said (e.g., oh really, uh-huh) than when teachers ask follow-up, yes/no or wh-questions to request further details (Dillon, 1985).…”