Objective vocal parameters in Farsi-speaking adults with Down syndrome.

Previous studies have indicated significant differences in vocal parameters between children with Down syndrome and normal children. This study was performed to see whether there is a significant dissociation between normal adults and adults with Down syndrome in terms of some vocal parameters. The participants were 22 adults with Down syndrome and 22 normal adults matched for age and gender. We measured jitter, shimmer, fundamental frequency (F0), and maximum phonation time (MPT). The results showed a significantly higher F0 and a significantly lower jitter in the Down syndrome group compared to the control group, while the average amounts of MPT and shimmer were not different. Moreover, the shimmer and jitter of females in both groups were lower than those of males. These findings might be the result of a physiological retardation of the larynx rather than mental retardation in the Down syndrome population.