Examining Corrective Responses and Adaptive Responses to Formant Perturbations

The ability to detect and correct errors during and after speech production is essential for maintaining accuracy and avoiding disruption in communication. Thus, it is crucial to understand the basic mechanisms underlying how the speech-motor system evaluates different errors and correspondingly corrects them. This study aims to explore the impact of three different features of errors, introduced by formant perturbations, on corrective and adaptive responses: (1) magnitude of errors, (2) direction of errors, and (3) extent of exposure to errors. Participants were asked to produce the vowel /ε/ in the context of consonant-vowel-consonant words. Participant-specific formant perturbations were applied for three magnitudes of 0.5, 1, 1.5 along the /ε-æ/ line in two directions of simultaneous F1-F2 shift (i.e., shift in the ε-æ direction) and shift to outside the vowel space. Perturbations were applied randomly in a compensation paradigm, so each perturbed trial was preceded and succeeded by several unperturbed trials. It was observed that (1) corrective and adaptive responses were larger for larger magnitude errors, (2) corrective and adaptive responses were larger for errors in the /ε-æ/ direction, (3) corrective and adaptive responses were generally in the /ε-ɪ/ direction regardless of perturbation direction and magnitude, (4) corrective responses were larger for perturbations in the earlier trials of the experiment.