Individual variability in auditory feedback processing: Responses to real-time formant perturbations and their relation to perceptual acuity.

In this study, both between-subject and within-subject variability in speech perception and speech production were examined in the same set of speakers. Perceptual acuity was determined using an ABX auditory discrimination task, whereby speakers made judgments between pairs of syllables on a /ɛ/ to /æ/ acoustic continuum. Auditory feedback perturbations of the first two formants were implemented in a production task to obtain measures of compensation, normal speech production variability, and vowel spacing. Speakers repeated the word "head" 120 times under varying feedback conditions, with the final Hold phase involving the strongest perturbations of +240 Hz in F1 and -300 Hz in F2. Multiple regression analyses were conducted to determine whether individual differences in compensatory behavior in the Hold phase could be predicted by perceptual acuity, speech production variability, and vowel spacing. Perceptual acuity significantly predicted formant changes in F1, but not in F2. These results are discussed in consideration of the importance of using larger sample sizes in the field and developing new methods to explore feedback processing at the individual participant level. The potential positive role of variability in speech motor control is also considered.