Caracterização acústica do contraste de sonoridade das consoantes plosivas

Abstract

The plosives of Brazilian Portuguese can be distinguished through their place of articulation, as well as through their voicing contrast. The voicing contrast of these phonemes can be perceived through some acoustic cues.This study had as aim to investigate and to compare the acoustic characteristics of voiced and voiceless plosives in children with typical phonological development (DFT), with phonological disorder (DF) who present difficulty to establish the distinctive features [+voice] of plosives, and adults with typical speech patterns of the language. In cases of DF with alteration of the feature [voice], the analysis of acoustic parameters responsible for the contrast between voiced and voiceless sounds can be useful during the whole therapeutic process, propitiating an objective and reliable return of the speech production possibilities of the subject to the therapist. For this, it is also necessary to have a previous comprehension of the acoustic values which are considered as normal . For this investigation, 33 subjects were selected and divided in three groups adult group (GA n=17), children group with DFT (GDFT n=11) and children group with DF (GDF n=5). Through pseudowords (papa, baba, tata, dada, kaka, gaga) inserted into carrier phrases, the voice onset time (VOT), the vowel length, the burst amplitude and the occlusion length were measured, with the aim to compare the acoustic registers of voiced and voiceless plosives in each group and among the groups: GA versus GDFT and GDFT versus GDF. The results showed that in the GA all acoustic registers were used in a different way between voiceless and voiced plosives. The same was observed for the GDFT, except for the burst amplitude, which presented few significant differences. For the GDF was not observed significant differences in the use of acoustic parameters according to the voicing of the plosives. The comparison between the groups GA and GDFT presented many similarities in relation to the implementation of the parameters that are responsible for the plosives voicing contrast. Thus, it was found that the children with DFT have already showed a dominion of the feature [voice]. It is also important to mention that, even not so frequent, were also found some differences among the groups. They are, in general, in medial onset position and unstressed syllable. These results suggest that this position and syllable nature provide an adverse context for the production of plosives. After comparing of the groups GDFT and GDF, it was observed through statistically significant results that the difference between the DFT and the system with disorder are basically through of the VOT and of the occlusion length of voiced plosives. These parameters seem to mark the difficulties of children with DF in distinguishing properly the voicing contrast of plosives consonants. So, the hypothesis which guides this research seems to be confirmed in part. It happens because the children with DFT are able to handle the acoustic parameters used to produce the voicing contrast of plosives. In children with DF and difficulty in establishing the marked value of the feature [voice], even if they do not establish the differences between voiceless and voiced plosives, they showed an approximation of some values of the GDFT.