Voice Onset Time among Children with Phonological Impairment.

Sammanfattning: Speech production requires cooperation between cognitive, linguistic and motor processes. It also requires spatial and temporal control of muscles, as well as simultaneous and coordinated activity of respiration, phonation and articulation (Cheng, Murdoch, Goozée & Scott, 2007; Yorkston, Beukelman, Strand & Bell, 1999; Raphael, Borden & Harris, 2011). Voice Onset Time (VOT) reflects the timing between phonation and articulation (Hoit-Dalgaard, Murry & Kopp, 1983). VOT is the most reliable acoustic cue for distinguishing between voiceless or voiced plosives (Auzou et al. 2000). Studies of English-speaking children with phonological impairment have shown atypical VOT-patterns (Bond & Wilson, 1980). The aim of the present study was to investigate Voice Onset Time (VOT) among Swedish children with phonological impairment and to examine if their VOT-values differ from typically developed Swedish children. Participants were 38 children aged 4;2−11;6 distributed over eight age- groups and five developmental stages of phonology. Audio recordings of minimal pairs were made at preschools, schools or at speech pathology clinics. The results indicated that children with phonological impairment produced VOT with deviant values and with a great variability. A marked acoustic difference between voiceless and voiced stop consonants was present, but not in all cases. Since the VOT-values were distributed over the group of children with phonological impairment, no developmental trend toward adult-like values that could be related to increasing age was found for either the acquisition of producing VOT or the acquisition of producing voicing lead. No differences in VOT were seen between the children in different phonological developmental stages or ages. No correlation between the degree of deviance of VOT and the proportion of Procent Phonemes Correct (PPC), age or phonological processes were found. From the results the conclusion can be drawn that children with phonological impairment have deviant VOT-values that could be caused by lack of phonological knowledge, but in particular since the variability did not decrease with increased age, have difficulties with motor execution.