Unpredictable temporal feedback perturbation dissociates mismatch detection from correction

This study investigates the online response of the speech motor control system to temporally perturbed auditory feedback using a novel Unpredictable Temporal Feedback Perturbation (UTFP) paradigm. Unlike Adaptive Temporal Feedback Perturbation (ATFP), in which predictable perturbations induce adaptation over repeated trials, UTFP applies brief temporal perturbations at random times on random trials to isolate the immediate, online response of the system. Perturbations were applied within productions of the phrase “I saw papa yesterday,” where papa had either a strong–weak or weak–strong stress pattern. We examined effects of the perturbation on segmental duration and local relative speech rate in the target word papa. Our results show that, in contrast to ATFP responses, UTFP responses are delayed, manifesting as a transient slowing of speech approximately 300–600 ms after the perturbation, and that the response effect is always lengthening, rather than being compensatory, as observed in ATFP. This suggests the UTFP response is driven by a generic sensory mismatch detection mechanism, not a mismatch correction system. Similar to ATFP responses, we found that UTFP response magnitudes are modulated by phonological structure, being larger in vowels than consonants, in stressed than unstressed syllables, and in word-final than word-initial syllables. Substantial interspeaker variation in the timecourse of UTFP responses was correlated with speech rate, suggesting a relation between rate of speech and attention to sensory feedback.