CDIS 4213 Chapter 7: Speech Science Reading #7 - Source charateristics

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Communication Disorders
CDIS 4213
Mary Toner

SOURCE CHARACTERISTICS The source components for speech are respiration and phonation. 1. How does respiration contribute to the final speech product? Respiration is the power source for sound. It serves as either the force that sets the vocal folds into vibration for a quasiperiodic sound (PHONATED SOUND) or it provides the air source which becomes turbulent as it passes through a vocal tract constriction (NONPHONATED SOUND). In respiration for speech, inspiration takes place through the action of the inspiratory muscles. These same muscles then control expiration to maintain an appropriate and continuing airflow through the vocal folds. As the volume of air in the lungs decreases, the inspiratory muscles eventually become relaxed and recoil and gravity effect continued exhalation. If speech continues further, the expiratory muscles act to push more air out of the thorax. The combination of these forces results in a fairly constant and consistent supply of air to the vocal folds and vocal tract. 2. How do phonated and nonphonated sounds differ in their source characteristics? When the vocal folds do not valve the air by their vibration, the air flow from the lungs becomes turbulent as it passes through vocal tract constrictions. The constriction may be at the level of the vocal folds (like in a whisper) or it may be in the oral cavity (producing s, f etc). These are nonphonated or voiceless sounds. If the vocal folds valve the air, the sound is phonated. This type of sound has more potential for variation in pitch, loudness, etc. 3. What comprises a cycle of vocal fold vibration? A cycle of vocal fold vibration as consists of 3 phases: Closing Phase the glottis narrows causing the air flow from the lungs to increase in velocity and the pressure at the point of constriction subsequently drops. This effect of increased velocity of air flow traveling perpendicularly to a constriction resulting in a drop in pressure at the constriction is known as the BERNOULLI EFFECT. Closed Phase when closure is complete along the entire medial surface of the folds (MEDIAL COMPRESSION), the pressure begins to build under the vocal folds. This pressure is called SUBGLOTTAL PRESSURE (SGP). SGP is determined by the flow of air from the lungs and the resistance provided at the level of the glottis (GLOTTAL RESISTANCE). SGP = Flow * Resistance
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