Partial compensation for altered auditory feedback: a tradeoff with somatosensory feedback?

Talkers are known to compensate only partially for experimentally-induced changes to their auditory feedback. In a typical experiment, talkers might hear their FI feedback shifted higher (so that/epsilon/ sounds like /ae/, for example), and compensate by lowering FI in their subsequent speech by about a quarter of that distance. Here, we sought to characterize and understand partial compensation by examining how talkers respond to each step on a staircase of increasing shifts in auditory feedback. Subjects wore an apparatus which altered their real time auditory feedback. They were asked to repeat visually-presented hVd stimulus words while feedback was altered stepwise over the course of 360 trials. We used a novel analysis method to calculate each subject's compensation at each compensation step relative to their baseline. Results demonstrated that subjects compensated more for small feedback shifts than for larger shifts. We suggest that this pattern is consistent with vowel targets that incorporate auditory and somatosensory information, and a speech motor control system that is driven by differential weighting of auditory and somatosensory feedback.