Current Primary Focus of Laboratory Research
The research of this laboratory focuses on neural mechanisms controlling the voice and the larynx. For the past ten years, we have been working on the development of a new, non-invasive technique for this study. We have found that when people hear their own voice through earphones, and when the voice pitch through the earphones is unexpectedly changed upwards or downwards, people automatically adjust the pitch of their voice. This adjustment represents a way the neural mechanisms controlling the voice respond to auditory feedback. This phenomenon also indicates that there is a close coupling between the auditory system's monitoring of voice and the motor system for adjusting the laryngeal system for voice output. Thus, this new technique provides us with a way of exploring how auditory feedback is used to help control vocal output.
We are now beginning to study the pitch-shift reflex in patients with brain damage. This work will help us define which areas of the brain are involved in this reflex. We are also beginning to study voice loudness control in a similar fashion to the way we have studied voice pitch control. We hope to learn if mechanisms for control of voice loudness are similar to those controlling voice pitch.
In order to relate our findings on changes in voice pitch or loudness to variations in auditory feedback more directly to neural mechanisms, we are beginning some new projects at this time. We are beginning to record cortical evoked potentials from subjects as they sustain vocalizations and hear pitch-shifted voice feedback. The potentials we have analyzed thus far indicate that the pitch-shift stimuli elicit neural potentials that we can record from the scalp of the subjects. We are also beginning to record electromyographic signals from intrinsic laryngeal muscles while people are receiving pitch-shifted voice feedback. These data provide us with data on how different laryngeal muscles react to changes in voice pitch or loudness feedback. In the near future, we will start doing the pitch-shifting experiments and using fMRI techniques to image brain locations that are active during these responses.
To enhance the effectiveness of our studies, we are attempting to develop a model of the auditory-vocal control system. As we define certain aspects of the model, the model itself will require further specification of details of the system. Thus through the use of the model, we anticipate a systematic exploration of critical variables and attributes of this system.