Speech Physiology Laboratory

UNC Craniofacial Center

David J. Zajac, Ph.D.

Associate Professor/Director

e-mail: david_zajac@dentistry.unc.edu

    The Speech Physiology Laboratory is dedicated to understanding the physiologic basis of speech production in individuals with normal speech and various disorders. A major focus of the laboratory is the investigation of individuals with cleft lip and/or palate. The laboratory has the capacity to analyze speech at various levels of production including the electromyographic (EMG), aerodynamic, and acoustic. Some past and current projects of the laboratory are described below.


Illustration of EMG recording of lower lip muscle
activity during speech. 


 


Projects:
 

The goal of this project is to describe respiratory behavior of children with and without cleft palate during speech production. Measures of both absolute respiratory volume per utterance and volume relative to vital capacity are determined. Vital capacity and expiratory reserve volumes are obtained using a heated pneumotachograph. Respiratory volume levels during speaking are then determined using circumferentially-vented mask pneumotachography. Previous studies have suggested that speakers with velopharyngeal (VP) dysfunction may use (i) greater respiratory volumes and (ii) shorter breath groups than speakers with adequate VP function. In addition, this ongoing study will explore relationships among lung volume levels and perceptual-physiological speech characteristics.


Illustration of adult speaker performing a vital capacity maneuver. A heated Fleisch #3 pneumotachograph is used to record expired respiratory airflow. Vital capacity volume is determined by integration of the airflow signal.

 Click here to view Vital Capacity graphic

Illustration of oral-nasal circumferentially-vented pneumotachograph mask (Glottal Enterprises, Syracuse, NY ). The mask is partitioned into nasal and oral chambers. Each chamber has fine mesh, wire screens that serve as flow-resistive pneumotachographs. Catheters (not visible in photograph) are inserted into each chamber to detect pressure variations associated with airflow. A microphone (also not visible in photograph) is positioned outside of the mask to record the audio signal. Integration of the airflow signals is done to determine lung volumes associated with speech utterances (see graphic #2). An additional catheter (visible in the photograph) is inserted through the oral chamber and positioned in the mouth to detect oral air pressure (see graphic #1). PERCI-SARS software ( Microtronics, Chapel Hill, NC ) is used to display and analyze the aerodynamic and acoustic data.

 Click here to view Oral-Nasal Mask graphic #1

 Click here to view Oral-Nasal Mask graphic #2

Why do individuals with cleft palate and velopharyngeal inadequacy (VPI) usually maintain intraoral air pressure of approximately 2-3 cm H2O during production of voiceless stop-plosives? One theory is that online feedback mechanisms signal the respiratory system to increase effort to maintain the oral air pressure pulse at minimally useful levels (see manuscript #11 under Publications). Another theory is that the inherent physiologic and aerodynamic properties of the respiratory system will maintain these pressures without the need for active feedback and regulation. The purpose of this study is to examine the oral and subglottal air pressure responses of speakers without cleft palate to sudden and unexpected loss of air pressure during production of /p/. An electronically controlled perturbator is used to quickly vent oral air pressure from a mouthpiece while the speakers repeat the syllable /pa/. The perturbator is programmed to open to various areas ranging from 5 to 40 mm2 during the pressure rise for /p/. The magnitude and rise (slope) of oral air pressure is recorded. In a small subgroup of speakers, subglottal air pressure is directly and simultaneously recorded by means of a catheter inserted through the cricothyroid membrane.

Mark Weissler, MD, is co-investigator. This study has been recently completed (see manuscript #25 under Publications).

Young children with Fragile X syndrome typically exhibit reduced speech intelligibility. As part of this study, we are investigating some acoustic characteristics of the speech of these children. Voice recordings are analyzed to determine speaking rate, sound segment duration, and vowel formant frequency. Preliminary analyzes indicate that increased speaking rate and reduced/deviant vowel space may be associated with decreased intelligibility (see graphic below).

Click here to view Vowel Space graphic

 

        

Individuals with severe dental malocclusion often produce sibilants such as /s/ and /sh/ with perceptual distortions due to deviant positioning of the tongue and/or teeth. Because of the underlying structural component, behavioral speech therapy often fails to modify speech distortions caused by malocclusion. Although orthognathic surgery may result in a normal dental relationship, the effects on speech are unclear. Indeed, one study has reported that while speakers initially demonstrated improved articulation post surgery, many reverted to presurgery patterns within a year.

Sarah Johnson, a senior at UNC-CH, was awarded a 2003 Summer Undergraduate Research Fellowship sponsored by the Frances C. and William P. Smallwood Foundation to study the effects of orthognathic surgery on speech production. Sarah recorded speakers with Class II and Class III malocclusions before and after surgery. Speakers produced the sibilants /s/ and /sh/ in 80 words embedded in a carrier phrase in a sound-attenuated booth. Sarah used the Computerized Speech Lab (Model 4400, Kay Elemetrics, Inc.) and spectral moment analysis (Milenkovic, 1999) to describe the acoustic properties of the sibilants. Non-surgical speakers with Class I occlusions also were studied for comparison purposes.

Sarah Johnson

Sarah Johnson analyzes a speaker's production of "Say seat again."

Click here to view Spectral Moments graphic

Last Updated: 12/15/06