  A transversal study of the pitch variability of parkinsonian voices in read
speech is presented. 30 patients suffering from Parkinson's disease (PD) and 32
healthy speakers were recorded while reading a text without voiceless phonemes.
The fundamental frequency contours were calculated from the recordings, and the
following measures were used for describing them: mean, minimum, maximum, and
standard deviation of the estimated fundamental frequencies. Results based on
these measures indicate that the influence of PD on some aspects of intonation
can be masked by the effects of aging, especially for male voices. However,
some parameters such as the relative fundamental frequency range exhibit lower
correlations with age than with PD stage, as evaluated using the Hoehn and Yahr
scale. These correlations between relative fundamental frequency range and PD
stage reach moderate-to-high values in the case of women. Additionally, three
parameters describing the form of the fundamental frequency modulation spectrum
were investigated for correlation with age and PD stage. The study of this
modulation spectrum provides some insight into the ability of the speakers to
plan the intonation of full phrases. For both male and female populations,
significant correlations were found between parameters obtained from the
modulation spectrum of fundamental frequency and the PD stage. Nevertheless,
the quantitative assessment of the performance of regression models built from
these modulation parameters and fundamental frequency range suggests that such
measures are likely to be of limited value in the early diagnosis of PD due to
inter-speaker variability.
