Some Relationships Between Vocal Intensity and Rated Nasality

Abstract

The effect of intensity variations on the degree of nasality perceived by the listener is of interest to those concerned with the assessment and treatment of nasal voice. It is generally accepted (4, 6, 8) that one outcome of coupling the nasal to the vocal tract, assuming a constant input, is to reduce the overall intensity of the speech signal. There is also evidence that severely nasal subjects tend to speak at lower intensity levels than those with mild nasal quality. Weiss (12) reports, for example, a negative correlation (r : —.57) between measures of average overall sound pressure levels and nasality ratings. While nasal quality appears to be related to the mean vocal intensity of the speaker, there is relatively little data concerning changes in the perception of nasality that might occur when subjects produce speech at different vocal intensity levels. In one of the few studies directly related to this topic, Hess (7) asked each of fifteen male cleft palate speakers to phonate each of six vowels at each of two pitch levels, an habitual pitch level and a pitch level 1.4 times higher, and at two intensity levels, 75 and 85 dB SPL. Nasality was rated along a seven-point scale. He found a lower mean nasality rating at the higher than at the lower intensity level. The difference between the means for the two intensity levels while statistically significant was relatively small, amounting to .25 scale value. Hess' findings are compatible with those of Williamson (13) who reports a decrease in nasality with in— creased vocal intensity in functionally nasal speakers. There are correlative data that bear on this question. Studies utilizing the probe-tube microphone assembly (1, 3, .9, 12) with cleft palate and functionally-nasal speakers have shown that measures of the difference, in decibels, between nasal and oral (overall) intensity are positively corre— lated with nasality ratings. There is some evidence in studies of normal (11) and cleft palate (9) speakers that the size of the sound pressure difference varies as a function of overall vocal intensity. These studies indicate that the size of the sound pressure difference tends to decrease as