Are retroflex-to-dental sibilant substitutions in Polish children's speech an example of a covert contrast? A preliminary acoustic study

The study aimed to investigate whether the dental substitutions of retroflex voiceless fricatives (/ù/to [s]) in Polish children's speech are an example of a covert contrast. We analyzed speech samples collected through a picture naming test from 11 children showing this retroflex-to-dental production pattern. The language material included words with/ù/and/s/in various word positions. We extracted a set of spectrum-based acoustic features from the recorded sibilants and conducted the analysis using linear mixed-effect models. The models showed that significant acoustic differences (p < 0.05) can be found between realizations of/s/and/ù/substituted by [s]. The main differences were detected in the amplitudes of fricative formants and the energy levels in specific subbands of the frication noise. The study provides preliminary evidence of the existence of covert contrasts in the analyzed substitutions.