Individual differences in auditory-motor integration revealed by speech fluency manipulations

A role for auditory feedback in maintaining fluency appears less specific than for pitch control, as one example, but delayed auditory feedback (DAF) clearly provides a potent manipulation of fluency. As most speakers are susceptible to DAF, we predicted DAF is particularly suited to identifying individual differences in auditory-motor integration. We conducted a series of studies to probe susceptibility to DAF-induced disfluency in 60 normally fluent speakers during conversation and oral reading. We further contrasted DAF effects on fluency with dual-task effects on fluency. During conversation and reading under DAF (250 ms delay), multivariate cluster classification indicated speakers show high, low, or intermediate susceptibility to disfluency. In contrast, dual-task effects on fluency appeared bimodal with individuals showing high or low susceptibility. DAF susceptibility was not related to dual-task disfluency in 41/60 speakers, but the remaining speakers were disfluent under DAF and dual-task conditions. When the DAF paradigm was extended to adults who stutter, most were classified as highly susceptible. The findings provide compelling evidence that individual differences need to be considered in auditory-motor integration research. Fluency is influenced by both auditory feedback and cognitive factors related to attention, which can inform theories of normal and disordered speech.