Intelligibility of distorted speech sounds shifted in frequency and time in normal children

Distorted speech sounds were presented to normal children aged 4-11 years and to young adults in such a way that 20 monosyllables were distorted with a 'speech stretcher' which produced frequency expansion and compression and also time expansion and compression. The experiment was performed to observe the intelligibility of such distorted speech sounds and the development of the discrimination ability in normal children. The results were as follows: (1) discrimination decreased sharply with increasing frequency change in both frequency-expanded and frequency-compressed speech; (2) discrimination was relatively unaffected by time expansion. However, with time compression there was a gradual decrease in discrimination at 50% time compression followed by a rapid deterioration at 75% time compression; (3) for a given percentage of distortion, frequency shift degraded intelligibility of speech sounds more severely than time shift, and (4) discrimination ability clearly increased with age in normal children. There was no significant difference between boys and girls.