Linguistics
'Um' and 'uh' aren't verbal clutter — they're doing a job
Linguists Herbert Clark and Jean Fox Tree analysed spontaneous speech and found 'uh' and 'um' aren't random disfluencies but function almost like words: speakers use 'uh' to flag a short upcoming pause and 'um' to flag a longer one, giving listeners advance warning of a delay. In their experiments, listeners actually recognised the next word faster after hearing 'uh' than after silence — the filler was helping them parse the sentence, not interrupting it.