| Abstract: | Distorted speech sounds were presented to 20 normal children, 5 normal adults and 68 mentally retarded children in such a way that 20 monosyllables were distorted with low-pass, high-pass and band-pass filtering. The experiment was carried out to observe the development of discrimination ability in normal young children and to compare it with that of the mentally retarded.(1) With unfiltered speech audiometry, 50–dB sensation level was enough for normal children to discriminate monosyllables. As for the mentally retarded, 10–20 dB above the average level of normal children was necessary to get correct discrimination. (2) Discrimination was poorest with low-pass filtering below 1200 Hz. (3) Discrimination was very good for both normal subjects and the mentally retarded with high-pass filtering above 1700 Hz. (4) There was a gap in discrimination between the two subject groups with band-pass filtering of 1200–2400 Hz. (5) There was a very great variation in discrimination scores from one subject to another, especially in the mentally retarded. (6) A clear developmental trend in discrimination ability was found in normal subjects. (7) There was no significant difference in intelligibility between boys and girls. |
