Measurements and analyses of nasal and oral airflow during isolated sound productions by normal and cleft palate speakers
Authors:   , Shih Jing-shihong 
Published: June 2024

Speech sound is produced through the superimposition of a coordinated series of progressive and dynamic processes. These processes include respiration, phonation, resonance, and articulation and are accomplished by making use of the vegetative tract, including all of the physiological airway and parts of the physiological foodway, which constitutes the set of biological transducers. The speech mechanism consists of the lungs as the airstream supplier, the larynx as the complex tone generator, a series of cavities (the trachea, the laryngopharynx, the oropharynx, the oral cavity, the nasopharynx, and the nasal cavity) as the resonator, and the tongue, teeth, jaw, and lips as the articulators. The anatomic-physiologic intactitude of these structures is required in the production of normal speech sounds. Normal speech requires normal physiological processes and in addition is dependent upon normal psychological and neurological perceptual processes which convert sound signals into perceived messages through the hearing mechanisms. In general, speech is a complicated process due to the specificity of its component parts. In addition, these parts are interrelated and inter-dependent on each other to the extent that an impairment of one may have a resultant effect on another. The complex nature of the speech process has remained a research interest and effort for many years. The cleft palate patient is beset by all these complications of normal speech as well as by some that are specific to his defect. Anatomically, his velopharyngeal cavity does not allow for a normal coupling of the resonance capabilities between the nasal and oral cavities. The coupling action of the velopharyngeal mechanism is carried out by very delicate and rapid movements of the soft palate, uvula, tongue, and pharyngeal wall. If specific muscles are denervated, or if the soft palate has suffered considerable scarring, complete and rapid coupling and uncoupling of the nasal and oral resonating chambers are not always possible. Inadequate velopharyngeal closure may result in the nasal emission of air and a nasal resonance quality, hypernasality, in the patient's speech. Past studies have shown that cleft palate speech defects result primarily from this velopharyngeal incompetence. Various types of experimental techniques have been developed for the study of the velopharyngeal function for both normal and abnormal speech. These techniques are classified as objective methods, as opposed to the subjective listener's nasality judgment method, and can be grouped into five general categories: (1) techniques for measuring nasal and oral air flow and pressure, (2) techniques involving measurement of nasal and oral sound intensity, (3) techniques involving evaluation of the acoustic spectrum, (4) techniques involving investigation of related muscular activities, and (5) techniques involving observation of anatomical action through the employment of X-ray photography methods. These techniques have also been used in combination. In this regard, cineradiography has been combined with spectrography for the study of sound quality, with electromyography for the study of muscular movement, and with anemometery or pneumotachography for the study of airflow. These newly developed techniques have gradually yielded new information and have made possible new insights into the speech processes. However, most of these techniques have remained in the research laboratory category. That is, they have fallen short of yielding clinically usable procedures and modest-cost, operationally-simple instrumentation. The present study is directed at simplifying air flow measurement techniques for the speech process and at establishing soundly based criteria for allowing convenient and meaningful clinical use of these measurements in determining and describing the degree of cleft palate speech deficiency.