ACOUSTIC CHARACTERISTICS OF SPEECH AND SELECT MEASURES OF BODY PHYSIOLOGY

The purpose of this research was to study the relationship between age-related changes in body physiology and acoustic characteristics of speech. To this end, measurements of mean fundamental frequency, semitone standard deviation (STSD), jitter, shimmer and maximum phonation range were made from voice samples produced by subjects representing three chronological age groups (25-35, 45-55 and 65-75) and two levels (good and poor) of physical condition. The physical condition of each subject was determined by measuring the following variables, known to reflect physiologic status: resting heart rate, resting stolic blood pressure, resting diastolic blood pressure, percent fat, preferred hand grip strength, forced vital capacity, height and weight. From a group of approximately 90 subjects, the 8 in each of the three chronological age groups who performed the best of these measures and the 8 who performed the worst, comprised the experimental population (n = 48). Results indicated that subjects in good physical condition produced maximally sustained vowels with significantly less jitter and shimmer and had larger phonation ranges than did subjects of similar chronological ages but in poor physical condition. Significantly larger STSDs and more shimmer were measured in maximally sustained vowels produced by old age subjects than were measured in similar production by young age subjects. These findings support the hypothesis that physical condition is a significant factor in the analysis of acoustic characteristics of speech. Of considerable import was the observation that acoustic differences, similar to those reported by others who compared the speech of young and old subjects, were found in the speech of subjects of the same chronological age, but in different physical conditions. These differences were particularly apparent when comparing the speech of old subjects in good and poor physical condition. In the absence of systematic variation in intensity, these acoustic characteristics were interpreted to reflect differences in the laryngeal mechanisms of these old subjects. Consistent with characteristics of general body physiology, it was therefore proposed that the laryngeal mechanisms of old subjects in poor physical condition have progressed farther in the physical aging process than have the laryngeal mechanisms of old subjects in good physical condition. Differential degenerative changes in the cellular, muscular, neuromotor and cartilaginous systems of the larynx were proposed as possible sources for these acoustic differences. In addition, subject motivational factors were considered of importance in the phonation range difference measured between young subjects in good and poor physical condition. The observation that acoustic characteristics of speech differed only in maximum performance speech tasks was interpreted in relation to performance breakdowns during stress testing. Although further research is necessary to substantiate these findings on a larger population, the differences observed here do have important implications for the study of aging. The data appear to support the view that the laryngeal mechanism is yet another structure that is subject to change as the body ages. Of particular note is the relationship that aging of the general body, as reflected in body condition, has with the laryngeal mechanism. This relationship provides additional insight into the potential limitations of using chronological age as the only index of aging in speech studies