A Laminagraphic Study of Vocal Intensity

Abstract

It has been suggested that vocal fold cross-sectional area (or mass) varies as a function of vocal intensity. Since this notion has not been subjected to test, it was the purpose of this investigation to study the relationship of the coronal cross-sectional area and mean thickness of the vocal folds to variation in vocal intensity. Subjects included eight males chosen on the bases of age, absence of voice problems, and the ability to produce specified vocal tones easily. The range of fundamental frequencies that each subject could produce was determined by a standard procedure. Final selection was made on the basis of these data and all subjects had essentially the same pitch ranges. Subjects were required to produce each of three vocal pitches at three vocal intensities. Pitches were specified in relation to total pitch range and were located as proportions above the lowest sustainable tone. The 10%, 25%, and 50% points to the nearest semi-tone were used but since all subjects' ranges were similar, frequencies of 104, 139, and 233 cps represented these levels. Intensities were specified as the 15%, 50%, and 85% levels of each subject's vocal intensity range. These proportions were obtained by requesting each subject to produce the loudest and softest phonations possible at each of the three frequencies. Vocal intensity was controlled by an Altex M40 microphone, a B and K calibrated amplifier, and SUI Model 11 sound level monitor. This system was calibrated by the GR 759-B sound level meter which was originally used to obtain the intensity ranges. Laminagrams were made of subjects phonating each of these vocal pitch-intensity combinations and measurements made of vocal fold cross-sectional area and mean thickness. Statistical analysis was carried out by an AXBXS three dimensional analysis of variance design on a IBM 610 computer. Briefly, the results permit the following conclusions: (1) As expected, vocal fold cross-sectional area and mean thickness were systematically reduced with increases in fundamental frequency of phonation. (2) Since the F for area was not significant at the 5% level but the F for mean thickness was, there is some question concerning whether there are systematic changes in vocal fold cross-sectional area as vocal intensity is varied. This question and limitations of the study will be discussed. (This research was supported by a grant from the National Institute of Health.)