The Effect of Changes in Velopharyngeal Orifice Area on Vowel Intensity

Abstract

This investigation studied the influence of changes in velopharyngeal orifice size on vowel intensity in normal speakers when subglottal air pressure was controlled. Con— trolled variations in velopharyngeal orifice area were achieved by two different methods. The effective velopharyngeal orifice areas introduced into the subjects were verified aerodynamically. A reduction in vowel intensity (SPL) was recorded during the large experimental velopharyngeal orifice condition (50 mmz) when compared to a control condition. The clinical implications of these findings are discussed. A primary physiological deficiency affecting speech production in an individual with a cleft palate is the inability to achieve adequate closure of velopharyngeal valve. Speech clinicians have noted a reduction in the speech loudness level of speakers who do not achieve adequate velopha-ryngeal closure (Cotton, 1940; Weiss, 1954; Morris, 1968). Morris (1968) has proposed two possible explanations for this reduction in loudness. First, the speaker with velopharyngeal incompetence may reduce the loudness level of his speech in an attempt to minimize the obviousness of his communication problem. Second, additional damping of the acousti— cal speech signal may result from increased oronasalpharyngeal cou— pling accompanying velopharyngeal incompetence. Acoustical energy is radiated primarily through the oral cavity during non—nasal speech produced by a speaker with adequate velopharyngeal closure. However, during a " non-nasal " speech task acoustical energy may be radiated through both the nasal and oral cavities by a speaker with inadequate velopharyngeal closure. Increased coupling between the nasal and oral cavities substantially increases the damping characteristics of the speech mechanism (Curtis, 1942; Hattori et al., 1958; Fant,