Journal of Speech, Language, and Hearing Research 55(1):276-89.
Purpose: In individuals who stutter (IWS), speech fluency can be enhanced by altered auditory feedback, while it has adverse effects in control speakers. This indicates abnormalities in the auditory feedback loop in stuttering. Current motor control theories on stuttering propose an impaired processing of internal forward models which might be related to a blurred auditory-to-motor translation. Although speech sound perception is an essential skill to form internal models, perceptual acuity has not been studied in IWS so far. We tested the stability of phoneme percepts by analyzing participants’ ability to identify voiced and voiceless stop-consonants.
Methods: Two syllable continua were generated by systematic modification of the voice onset time. We determined speech perceptual acuity by means of discriminatory power in 25 IWS and 24 matched control subjects by determining the phoneme boundaries, and by quantifying the interval of voice onset times where phonemes were perceived ambiguously.
Results: In IWS discriminatory performance was weaker and less stable over time when compared to control subjects. In addition, phoneme boundaries were located at longer voice onset times in IWS. Conclusion: Persistent developmental stuttering is associated with less reliable phonological percepts, supporting current theories regarding the sensory-motor interaction in human speech.