1. Electromyograms (EMGs) were recorded from the right and left ventrolateral surfaces of the chest wall to study the activity of the diaphragm during three tasks: moderately deep breathing, speech production, and speechlike breathing in which subjects mimicked their speech breathing pattern but did not vocalize. In a second experimental protocol, activity of right and left masseter muscles was recorded in three conditions: chewing, rhythmic clenching, and speech. 2. EMGs were analyzed in the frequency domain by computing the average spectrum of 128-ms intervals selected from the rising phase of the EMG in 30 repetitions of each task. Coherence functions between bilateral pairs of EMGs were computed and examined for significant coherence in the range of 20-230 Hz. 3. In the deep breathing condition, significant coherence was present in two ranges, 20-60 Hz and 60-110 Hz. Oscillations in the 60- to 110-Hz range have long been associated with the operation of the primary respiratory pattern generator, and the present results replicate earlier reports of correlated oscillations in this range in bilateral recordings of human respiratory muscles during voluntarily controlled breathing. 4. In speech and speechlike breathing, correlated oscillations in the 60- to 110-Hz range were significantly reduced. This result supports the hypothesis that the neural circuitry characterized by high-frequency oscillations (HFOs) in the 60- to 110-Hz range, possibly a central pattern generator (CPG), is not the primary source of drive to respiratory motoneuron pools in speech. 5. During chewing, highly correlated oscillations were observed in right and left masseter activity. Significant coherence occurred in the range of 20-140 Hz, with very large peaks in the 20- to 60-Hz band. This result is interpreted in light of studies of rhythmic jaw movements elicited by cortical stimulation in experimental animals and studies of the reflex organization of the jaw-closing muscles. It is possible that highly correlated oscillations in the 20- to 60-Hz band arise from a central command system, such as a pattern generator, from reflexes, or from an interaction of central and reflex inputs. 6. In most subjects, nonzero coherence in the 20- to 60-Hz band also was observed during clenching and speech; however, levels of coherence in the 20- to 60-Hz band were significantly reduced in these conditions compared with chewing. 7. Taken together, the present results suggest that coherent HFOs observed in consistent frequency ranges across subjects are characteristic of human motor behaviors that are likely to involve pattern generation circuitry.

This study explores the effects of hearing status and bite blocks on vowel production. Normal-hearing controls and postlingually deaf adults read elicitation lists of /hVd/ syllables with and without bite blocks and auditory feedback. Deaf participants' auditory feedback was provided by a cochlear prosthesis and interrupted by switching off their implant microphones. Recording sessions were held before prosthesis was provided and one month and one year after. Long-term absence of auditory feedback was associated with heightened dispersion of vowel tokens, which was inflated further by inserting bite blocks. The restoration of some hearing with prosthesis reduced dispersion. Deaf speakers' vowel spaces were reduced in size compared to controls. Insertion of bite blocks reduced them further because of the speakers' incomplete compensation. A year of prosthesis use increased vowel contrast with feedback during elicitation. These findings support the inference that models of speech production must assign a role to auditory feedback in error-based correction of feedforward commands for subsequent articulatory gestures.

The goal of the present experiment was to determine if stuttering is associated with unusually high levels of activity in laryngeal muscles. Qualitative and quantitative analyses of thyroarytenoid and cricothyroid recordings from 4 stuttering and 3 nonstuttering adults revealed the following: Compared to periods of fluent speech, intervals of disfluent speech are not typically characterized by higher levels of activity in these muscles; and when EMG levels during conversational speech are compared to maximal activation levels for these muscles (e.g., those observed during singing and the Valsalva maneuver), normally fluent adults show robust and sometimes near maximal recruitment during conversational speech. The adults who stutter had a lower operating range for these muscles during conversational speech, and their disfluencies did not produce relatively high activation levels. In summary, the present data require us to reject the claim that adults with a history of chronic stuttering routinely produce excessive levels of intrinsic laryngeal muscle activity. These results suggest that the use of botulinum toxin injections into the vocal folds to treat stuttering should be questioned.

This study investigates the effects of speaking condition and auditory feedback on vowel production by postlingually deafened adults. Thirteen cochlear implant users produced repetitions of nine American English vowels prior to implantation, and at one month and one year after implantation. There were three speaking conditions ͑clear, normal, and fast͒, and two feedback conditions after implantation ͑implant processor turned on and off͒. Ten normal-hearing controls were also recorded once. Vowel contrasts in the formant space ͑expressed in mels͒ were larger in the clear than in the fast condition, both for controls and for implant users at all three time samples. Implant users also produced differences in duration between clear and fast conditions that were in the range of those obtained from the controls. In agreement with prior work, the implant users had contrast values lower than did the controls. The implant users' contrasts were larger with hearing on than off and improved from one month to one year postimplant. Because the controls and implant users responded similarly to a change in speaking condition, it is inferred that auditory feedback, although demonstrably important for maintaining normative values of vowel contrasts, is not needed to maintain the distinctiveness of those contrasts in different speaking conditions.

The provision of prosthetic hearing to postlingually deafened adults impaired their phonemic contrasts at first, as their auditory feedback had novel characteristics. Once auditory feedback became recalibrated with prosthesis use, it could, in turn, revise feedforward commands that control the contrasts in its absence.