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.

Background and Aim: Impairment in language content production, long-term memory and executive function in Parkinson's disease reported in several studies. Identification of these disorders is useful in planning for early interventions. The aim of this study was evaluation of semantic and phonemic clustering and switching in Parkinson's disease.

Methods: In this study, 30 patients with Parkinson's disease and 30 healthy individuals evaluated that were matched by age , sex and educational level . Clustering and switching average were compared between the two groups according to the Troyer method . Data recorded and analyzed using independent t test and Pearson correlation coefficient.

Results: Comparison of mean scores of clustering between patients with Parkinson's disease and healthy individuals indicated significant difference (p=0.05). In addition, significant difference was observed between mean score of switching in two groups (p=0.008).

Conclusion: The finding of the present study reveal that switching between semantic or phonemic subcategory and clustering impaired in patients with Parkinson's disease.