What is meant by average vocal fundamental frequency in parkinson's disease
Answers
In Parkinson’s Disease (PD), qualitative speech changes such as decreased variation in pitch and loudness are common, but quantitative vocal changes are not well documented. The variability of fundamental frequency (F0) in 32 individuals (23 male) with PD both ON and OFF levodopa medication was compared with 32 age-matched healthy controls (23 male). Participants read a single paragraph and estimates of fundamental frequency (F0) variability were determined for the entire reading passage as well as for the first and last sentences of the passage separately. F0 variability was significantly increased in controls relative to both PD groups and PD patients showed significantly higher F0 variability while ON medication relative to OFF. No significant effect of group was seen in the change in F0 variability from the beginning to the end of the reading passage. Female speakers were found to have higher F0 variability than males. F0 variability was both significantly reduced in PD relative to controls and significantly increased in patients with PD during use of dopaminergic medications. F0 variability changes over the course of reading a paragraph may not be indicative of PD but rather dependent on non-disease factors such as the linguistic characteristics of the text.
Parkinson’s disease is a neurological disorder characterized by the progressive loss of dopaminergic neurons in specific brain areas and occurs most prevalently in older adults (Lang & Lozano, 1998). Characteristic symptoms include tremor, rigidity, dyskinesias, and postural gait changes (Lang & Lozano, 1998). Vocal symptoms are also common, with speech deficits occurring in 60–80% of patients (Canter, 1963; Darley, Aronson, & Brown, 1969; Mutch, Strudwick, Roy, & Downie, 1986). The Parkinsonian voice has been described qualitatively as breathy, rough, hoarse, tremulous, abnormally pitched, having reduced pitch range, and unusually quiet (Holmes, Oates, Phyland, & Hughes, 2000).
Fundamental frequency (F0), a result of the rate of vibration of vocal folds, is perceptually related to vocal pitch. Some studies have found higher mean F0 values in individuals with Parkinsonian voice (Goberman & Blomgren, 2008), particularly in males (Canter, 1963; Holmes et al., 2000; Metter & Hanson, 1986; Skodda, Gronheit, & Schlegel, 2011). However, average speaking fundamental frequencies show considerable inter-speaker and intra-speaker differences due to intentional prosodic changes (Atkinson, 1976). A reduction in these intentional prosodic pitch changes can be measured by examining F0 variability, which has been shown to contribute to overall speech intelligibility in both healthy and dysarthric speakers (Bunton, Kent, Kent, & Duffy, 2001; Laures & Weismer, 1999).
Acoustic characterization of F0 variability has been realized in a variety of ways, including the range (difference between the passage maximum and minimum) of F0 excursions, F0 standard deviation (F0SD), and the semitone standard deviation (STSD), which is normalized for mean speaker F0. Although F0 range has been studied in PD previously, measures of range are highly corruptible by single time-points and thus are less appropriate estimations of overall prosodic variation. In this study we focus on F0SD and STSD. STSD has been used previously (Ramig, Countryman, Thompson, & Horii, 1995) as an intervention outcome measure in PD; it provides an estimate of passage prosodic variation that is less likely to be confounded by the effects of mean F0 (and thus speaker sex) and is also robust to single instances of F0 deviations. Although F0SD is somewhat robust against corruption from a minority of datapoints, it may be affected by mean F0. It has however been studied in individuals with PD by several groups (Gamboa et al., 1997; Goberman, Coelho, & Robb, 2005; Holmes et al., 2000; Jimenez-Jimenez et al., 1997; Skodda et al., 2011). Here we include F0SD in order to make comparisons to previous literature.
Results
The mean female UPDRS total score was 52.1 (SD=35.8, range = 9 – 97) and the mean male UPDRS score was 40.9 (SD =19.8, range = 9 – 91). Disease duration and OFF medication UPDRS scores were statistically significantly correlated (p = 0.003) with R = 0.50. Figure 1 shows F0SD, STSD, ΔF0SD, and ΔSTSD as a function of sex and group.