These include "false starts", i.e. words and sentences that are cut off mid-utterance; phrases that are restarted or repeated, and repeated syllables; "fillers", i.e. grunts, and non-lexical or semiarticulate utterances such as huh, uh, erm, um, and hmm, and, in English, well, so, I mean, and like; and "repaired" utterances, i.e. instances of speakers correcting their own slips of the tongue or mispronunciations (before anyone else gets a chance to).
[1] A disfluence or nonfluence is a non-pathological hesitance when speaking, the use of fillers (“like” or “uh”), or the repetition of a word or phrase.
[4] Research in computational linguistics has revealed a correlation between native language and patterns of disfluencies in spontaneously uttered speech.
linguistic research has suggested that non-pathological disfluencies may contain a variety of meaning; the frequency of uh and um in English is often reflective of a speaker's alertness or emotional state.
Some have hypothesized that the time of an uh or um is used for the planning of future words;[8] other researchers have suggested that they are actually to be understood as full-fledged function words rather than accidents, indicating a delay of variable time in which the speaker wishes to pause without voluntarily yielding control of the dialogue.
[9][10] Hmm is an exclamation (an emphatic interjection) typically used to express reflection, uncertainty, thoughtful absorption, or hesitation.
The first h-sound is a mimic for breathing out, and the second m-sound, since the mouth is closed, is representing that the person is not currently sure what to say (erm and um are used similarly).
Nicholas Christenfeld, a psychologist at the University of California, San Diego, and an expert on filled pauses, attests hmm is popular largely since it is such a neutral sound and that "it's easier to say than anything else".
[14] The use of hmm is typically used during "thoughtful absorption", which is when one is engrossed[15] in their flow of ideas and associations, that lead to a reality-oriented conclusion.