Acoustic assessment of the voices of children using nonlinear analysis: proposal for assessment and vocal monitoring.

Objective: To analyze the accuracy of recurrence measurements, both isolated and combined, to assess the intensity of vocal disorders in children.

Method: A total of 93 children of both sexes (48 girls and 45 boys), aged between 3 and 10 years, participated. The vocal-deviation intensity was evaluated by the consensus of three speech therapists from the pronunciation of vowel /ε/ using the visual analog scale. In the acoustic analysis, eight recurrence plot characteristics were evaluated and extracted with neighborhood radius values that maintained the recurrence rate at 1%, 2%, 3%, 4%, and 5%. The classification was performed using quadratic discriminant analysis applied for individual and combined measurements. The performance was evaluated by measuring the accuracy, which related the cases correctly classified to all the analyzed cases.

Results: In the classification cases concerning individual measure performance, the trapping time and maximum length of the diagonal lines showed the best classification potential to discriminate between healthy and disturbed voices, with accuracy rates above 80%. In the healthy and mild deviation cases, the trend (TREND) measure was also relevant. For the mild versus moderate deviation classification, the best performance was obtained by the TREND measure (85.00% ± 7.64%). A gain was obtained in the classification rate when the measures of recurrence were combined, reaching an accuracy of 95.00% ± 5.00%, for discriminating between healthy voices and those with mild deviation.

Conclusions: The measures of recurrence, either alone or combined, may be useful in detecting healthy and disturbed voices and in differentiating the intensity of vocal disorders in children.