ASTUDY OF THE PURE-TONE DISCRIMINATION IN DEAFMUTE

Abstract

Seventy eight cases of deafmute children (congenital deafmutes 43, acquired deafmutes 35 from the school for the deafmute associated with Tokyo University of Education) were investigated concerning loudness discrimination (differencelimen of loudness), threshold of pain and auditory area of pure tones at the frequencies of 4, 000, 1, 000 and 250cps. Results obtained were as follows:(1) The mean values of DL at 50% correct judgment at were found to be between 0.9dB and 1.2dB, and those of DL at 80% correct judgment were between 2.1dB and 2.8dB.(2) Difference limen of loudness measured at the intensity of "not too loud" and "not too low" showed significant difference at 4, 000 and 1, 000 cps between the congenital and acquired deafmutes.(3) Comparison of the DL with the normal DL measured at 40dB above the threshold of hearing was made and there was no significant difference between the congenital deafmute and the normal, but significant difference between the acquired deafmute and the normal.(4) Thresholds of pain were distributed between the threshold of pain and uncomfortable loudness level of the normal, and the auditory area of deafmutes became remarkably narrow.Part II. Pitch Discrimination and Equal Loudness Curves of DeafmuteSixty three cases of deafmutes (congential 33, acquired 27 from the school for the deafmute associated with Tokyo University of Education and female adults of acquired deafmutes 3) were studied on pitch discrimination (DL on pitch) and equal loudness curves (ELC).Results were obtained as follows:(1) It was found the DL on pitch (relative difference limen measured on ELC at 4, 000, 2, 000, 1, 000, 500 and 250cps) was distributed in wide range and showed the mean values of 10-20% which were much larger than the normal values.(2) It should be generally considered that ELC was separated widely from the auditory threshold curve in the lower frequencies, but slightly deviated from a parallel relationship with the threslhod curve in the higher frequencies. The ELC in the lower frequencies showed the opposite inclination to normal ELC. It was concluded that the changes in loudness sensation to the intensity of sound were more abrupt in higher frequencies than in lower frequencies.