THE VARIATION PROCESS OF RESIDUAL HEARING BY THE USE OF THE HEARING AID : Reversible Deterioration of Hearing Threshold on the Aided Ear and Frequency Response of a Hearing Aid

Abstract

There are some hearing impaired person whose hearing threshold level deteriorate on the aided ear, hearing aid usage ear and restore on the unaided ear, hearing-aid rest ear. Authors named such a phenomenon a reversible threshold shift with hearing-aid use. The purpose of this study was to investigate the deterioration and restration process of hearing acuity in the sensori-neural hearing impaired wearing hearing-aids and to discuss its relationship with the type of his hearing threshold shift and the acoustic frequency response of his hearing aids. Subject was a graduate student whose average hearing-threshold level was 80dB at 1,000Hz (better ear). He was provided the formation of language and speech by the acoustic method at preschool period. His speech discrimination score was 100% at 100dB (HL: JIS T1201) in 67 Japan Audiological Society Syllabic List. He has telephoned to a person with his personal hearing-aid and can comprehend conventional speech very well. His wearing hearing aid was a behind-the-ear type and its maximum power output was 136dB (SPL). Acoustic gain for input 70dB (SPL) at 300-4,000Hz was 42dB (SPL). The results were as follows: (1) The occurence of threshold shift due to hearing-aid usage was observed in a frequency range of 500-2,000Hz. It was of the typical valley type. (2) Deterioration of eharing threshold was less than 20dB when acoustic gain was held constant. (3) In the relation between deterioration process and restoration process of hearing threshold the restration rate of hearing acuity was was slower than the deterioration rate. Two weeks were needed after putting off the hearing aid for hearing threshold to be restored. (4) The deterioration range of hearing threshold was related to the acoustic features of frequency response with hearing-aids.