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Background and Aim: Parkinson’s disease (PD) is a progressive neurological disorder resulting from significant decrease of dopamine in the brain. The main and most common symptom of speech disorder associated with Parkinson’s disease, which is kind of dysarthria, is reduction in speech intelligibility. Since this disorder represents damages to acoustic aspects, researchers are attracted to study the relationship between these two disorders. In this study, we assessed the comparison of speech vowels between normal people and patients with Parkinson’s disease.

Methods: In this cross-sectional study, 18 voice samples of patients with Parkinson’s disease and the same number of samples from normal people in a voiceless environment were recorded and analyzed by Praat software. Data analysis was performed by independent samples and Mann-Whitney tests.

Results: All variables investigated in two groups showed significant differences. In adults with Parkinson’s disease , F1-F0 in low vowels showed a considerable reduction in respect to normal people (p <0.001). In addition, F2-F1 in high vowels represented a significant decrease in these patients (p<0.05).

Conclusion: The results indicate that Parkinson’s disease affects formant frequency in patients compared with normal people. Reduction in speech intelligibility can be accurately measured using acoustic procedure.

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Background and Aim : Nasalization of a vowel refers to the addition of nasal resonance to the vocal tract transfer function. Also, vowel nasalization occurs because of coarticulation. Coupling of the nasal resonating space to the oropharyngeal cavity alters the vocal tract formants in complex ways. The purpose of this study was to investigate the effect of nasalization on /a/ vowel formants in before and after nasal consonant.

Methods: In current cross-sectional study, voice samples of 60 normal children ranging the age of four-nine years were investigated. Participants were asked to repeat / ʔ ama/ three times and vowel /a/ after presentation of an auditory model. Then, obtained samples were analyzed using Praat 5.3.13 . Average of F₀, F₁, F₂ and F₃ were calculated for /a/ comes before and after /m/ in production of / ʔ ama/ over three trials.

Results: There were statistically significant differences of F₁, F₂ and F₃ between / a/ which proceeds nasal consonant and /a/ follows nasal consonant , the before nasal consonant /a/ versus single /a/ and the after nasal consonant /a/ versus single /a/ (p=0.001 for all).

Conclusion : F₁, F₂ and F₃ in /a/ before nasal consonant affected by anticipatory nasal coarticulation and in /a/ after nasal consonant affected by carry-over nasal coarticulation . This study showed nasal coarticulation and nasalization result in decreasing F₁, F₂ and F₃ in /a/ vowel.