Comparison of Involuntary and Volitional Responses to Pitch-Shifted Auditory Feedback: Evidence for Tone Speakers' Flexibility to Switch between Opposing and Following Responses

Purpose: Our audio--vocal system involves a negative feedback system that functions to correct for fundamental frequency (f[subscript 0]) errors in production. Therefore, automatic and opposing responses appear when an unexpected change in voice pitch is present in auditory feedback. This study explores following responses to pitch perturbation in auditory feedback in tonal language speakers, which have been commonly overlooked or discarded by past research. We examine whether the number of response types (opposing vs. following) and their dynamic f[subscript 0] contours in tone word production vary as a function of instruction (involuntary ["to ignore"] vs. volitional ["to compensate"]). Method: Twenty-four native speakers of Taiwanese Southern Min (TSM) produced three disyllabic TSM words while receiving pitch perturbation through headphones. The three disyllabic words were "tsau"[superscript 55]-"im"[subscript 55] ("out of tune"; HH), "kau"[superscript 33]-"uann"[superscript 33] ("exchange"; MM), and "pan"[superscript 11]-"an"[superscript 11] ("handle a case"; LL) that carry an identical high-, mid-, or low-level tone. The participants were instructed either "to ignore" or "to compensate" for the pitch shifts. Results: Results from a Bayesian Poisson regression show that the number of opposing and following responses were split nearly 50-50 for the "ignore" condition and 55%-35% for the "compensate" condition. The simulation results indicate that the speakers were able to switch between the feedback and the feedforward mode during the testing. On the other hand, f[subscript 0] contour analyses using generalized additive models show that pitch-increasing responses (i.e., oppose to downshifts or follow upshifts) were significantly larger than pitch-decreasing responses (i.e., oppose to upshifts or follow downshifts) for the MM and LL words, but not for the HH word. Conclusions: Our results provide support for the view that, for tone speakers, following responses are not uncommon. The magnitudes of pitch shift response trajectories have to do with the available pitch range for moving up or down in tone word production.