Factors Affecting Speech Intelligibility - A Developmental Study

Abstract

There is a dearth of research on speech intelligibility in typically developing Tamil speaking children and no published study was reported on the relation between factors such as phonetic accuracy, rate of speech, average amplitude, and frequency range in Tamil speaking children. The aim of this study is to investigate the development of speech intelligibility in typically developing Tamil speaking children in the age range of 2 to 6.11 years. A total of 150 typically developing native tamil speaking children between the age range of 2 and 6.11 years were further divided into 5 groups, with each group consisting of 30 children. Nine sentences in Tamil with increasing complexity was developed to study the developmental trend of speech intelligibility. Each child was seated comfortably and pictures of sentences were randomly presented one after the other as the investigator say the sentence describing the picture. The child was instructed to repeat the sentences after the investigator. Acoustic analysis was done using CSL Model 4500 and frequency range , intensity and rate of speech were calculated. Perceptual analysis was done using the transcription sheets, by a speech language pathologist. Subsequently, percentage of phoneme correct for words and sentences were calculated, separately. Independent ‘t’ test, pearson’s rank correlation, spearman’s rank correlation and regression analysis were conducted to find the predictor variables of speech intelligibility. Results revealed, percentage of phoneme correct increased with age and there were no significant gender differences for words and sentences. It was also found that PPC of sentences, intensity average and ROS has a strong positive correlation. As PPC values increases (with age), intensity and rate of speech also increases. Frequency range has no correlation with any of the variables like intensity, PPC and ROS.