Speakers with cleft palate could have various speech problems such as hypernasality, nasal air emission, weak consonants production, and compensatory articulation errors. These kinds of articulation errors could downgrade the speech intelligibility of...
Speakers with cleft palate could have various speech problems such as hypernasality, nasal air emission, weak consonants production, and compensatory articulation errors. These kinds of articulation errors could downgrade the speech intelligibility of cleft palate speakers, which cause them to be socially stigmatized by inducing significantly noticeable unnatural responses during communication with others.
However, the studies on the articulation problems in cleft palate speakers mainly have focused on identifying different types, characteristics, and causes of the articulation errors. There are very few studies of the influence on articulation errors of cleft palate on speech intelligibility and acceptability. Their focuses are restricted to the correlation between the numbers of articulation errors or the percent of correct consonants(PCC) and speech intelligibility or acceptability. So far, enough studies have not been conducted on the effect of the numbers of articulation errors or the PCC on the speech intelligibility and acceptability.
The purpose of current study was to examine how the PCC derived from the speech of the children with cleft palate have effects on the speech intelligibility and on the speech acceptability. For this purpose, the present study compared the PCC, speech intelligibility and speech acceptability of the children with those of functional articulation disorder and the normally developing children.
3~6 year-old 9 children with cleft palate, 9 children with functional articulation disorder, and 9 normal developing children participated in this study as speakers. All subjects were asked to repeat seven sentences made of 8 syllables. All sentences produced by subjects were audio and video-recorded. At the site of the recording, the judgment of the correct articulation of the target sound was made and then the PCC was calculated for each sentence.
All recorded data were randomized in order to prepare 3 sets of 84 sentences. After listening each sentence, 40 naive listeners were asked to rate both intelligibility and acceptability of each sentence on the 10 cm line of Visual Analog Scale.
The group comparisons for the percent of correct consonants revealed that PCC of the total sentences in cleft palate children was significantly lower than normal children. Of 7 sentences, cleft palate children showed significantly lower PCC than normal children in bilabial stops sentence, alveolar stop sentence, alveolar fricative sentence, and alveolopalatal africate sentence. Especially cleft children showed significantly lower PCC of alveolar stop sentence than the children with functional articulation disorder. However, no significant group differences among 3 groups were found in velar stop sentence, glottal fricative sentence. and alveolar liquid sentence. These results suggest that the main articulation error of cleft palate children group occurred in obstruents, and cleft children have a difficulty in the articulation of consonants having [+coronal] feature that is articulated by using the front half of a tongue, and consonants having [+anterior] feature that is articulated by using anterior part of the oral cavity.
The results of group comparison showed that children with cleft palate acquired significantly lower score of speech intelligibility than normal children group. They got significantly lower scores than normal children in all sentences except the alveolar liquid sentence. Although the group difference on PCC was not significant for velar stop sentence and glottal fricative sentence, the children with cleft palate got significantly lower intelligibility score than normal children. Various articulation errors that cleft palate made in velar stop sentence children might have negative effects on the judgment of target phoneme, which correspondingly lower its intelligibility. Although the PCC of glottal fricative sentence was high in cleft palate children group, it is considered that the hypernasality and voice quality of cleft palate children had bad effects on the judgment of target phoneme by lowering the intelligibility. Although significant difference was not found between cleft palate children group and functional articulation disorder children, the study revealed that cleft palate children group tended to show slightly higher intelligibility than functional articulation disorder children group in all sentences except the alveolar stop sentence. Even though articulation errors were observed more in the cleft palate children group than in the functional articulation disorder children group, the major articulation errors of cleft palate children turned out to have less negative effects on the intelligibility rating. Relatively, the distortion and substitution errors that were mainly observed in the functional articulation disorder children group might have negative effects on the intelligibility rating.
The results of the group comparison of speech acceptability revealed that the cleft palate children group generally showed significantly lower acceptability than normal children group. Of 7 sentences, the cleft children group showed significantly lower speech acceptability than the normal developing children in alveolar stop sentence and alveolopalatal africate sentence. There were no significant group differences in PCC between the cleft palate group and the normal child group for velar stop sentence, glottal fricative sentence and alveolar liquid sentence. However, cleft palate children group showed significantly lower PCC than normal children group for bilabial stops sentence, alveolar stop sentence, alveolar fricative sentence and alveolopalatal africate sentence. Unlike other sentences, cleft palate children group showed higher PCC in the bilabial stops sentence than in other sentences. Significant group difference in intelligibility rating was found in the alveolar fricative sentence showing relatively lower PCC than other sentences in all three children groups. But in alveolar stop sentence and for alveolopalatal africate sentence the cleft palate children group showed significantly lower speech acceptabilities than normal developing children group.
Based on these results, the rating score of speech acceptability was found to be largely differentiated by the PCC score. Namely, the rating score of speech acceptability was significantly lowered in the sentence having noticeably low PCC. Especially, the rating score of speech acceptability was significantly low in those of sentences which showed typical articulation errors by the cleft palate children group.
Based on the results of group comparisons of PCC, intelligibility, and acceptability, it is possible that the intelligibility of cleft palate children was rated low even if the cleft palate children showed no significantly lower PCC compared to normal children in specific sentences. These results may come from the typical articulation errors, resonance, and sound quality characteristics of the cleft palate children. However, the rating for speech acceptability was found to be largely dependent on the correctness of articulation. In another words, intelligibility was greatly downgraded by the sentences with significantly low PCC. And these results suggest that the relationship of speech intelligibility and acceptability could change depending the level of PCC.
Although the present study compared the PCC, intelligibility and acceptability of cleft palate children group to those of functional articulation disorder children and normal developing children groups, the study included limited number of participants and controlled only participants' age. So, there is a limitation in generalizing the results of the current study. The study also devised the sentences controlling the length of utterance, intensity, number of target consonants, and speech rate to acquire more appropriate sample of speech data for the measurement of speech intelligibility and acceptability. Therefore, the study did not analyze the effects of correct articulation of each segmental sound on speech intelligibility and speech acceptability in detail.
In spite of these limitations, the significance of the present study is in the pont that the study conducted the experimental study to know the effect of articulation errors on speech intelligibility and acceptability in cleft palate children through the comparison with functional articulation disorder children and normal children who do not have any organic causes. And the study could be placed on the provision of preliminary data on how the naive listener who are importantly regarded as the counterpart of communication in daily life understand the articulation errors of cleft palate children and how they accept it.