Speech Physiology Laboratory
The research of this laboratory focuses on neural mechanisms controlling the voice and the larynx. For the past twenty years, we have been working on the development of a non-invasive technique for the study of the role of auditory feedback on voice control. We have found that when people hear their own voice unexpectedly shifted in pitch or loudness through earphones, they automatically adjust the pitch or amplitude 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.
In our most recent studies, we have focused on the study of neural mechanisms underlying these reflexes using EEG and fMRI techniques. In the EEG studies, we have found that cortical event-related potentials (ERPs) triggered by pitch-shift stimuli occurring at the onset of vocalization are suppressed in comparison to passive listening to the same shifts in voice auditory feedback. On the other hand, ERPs triggered by pitch-shift stimuli presented during vocalization are enhanced relative to ERPs triggered by passive listening to the same stimuli. In addition, if the shifts in voice pitch feedback are unpredictable, the ERP magnitudes are larger than if the stimuli are predictable. The ERP magnitudes are also enhanced in young adults with ADHD. In musicians with perfect pitch, the neural processing of the shifts in voice pitch feedback occur in the left hemisphere at an earlier point in time in comparison with musicians with relative pitch capabilities. Our studies using fMRI techniques have demonstrated enhanced BOLD responses in the left and right hemisphere in the superior temporal gyrus in response to voice pitch-shifted feedback.
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.