TEMPORAL RESOLUTION WITH HEARING-AID IN H EARING-IMPAIRED PATIENTS

The purpose of hearing aid fitting is to improve the communication of the hearing impaired. Despite rigorous efforts to optimize hearing aid fitting there are still some patients who remain unsatisfied. The sub ject of research was to find improved methods of measuring, to increas e the correlation between subjective information from the patient and objectively measurable data. With this goal in mind the variation of t emporal resolution in hearing aid fitting was investigated in 88 patie nts comparing unaided and aided hearing basing on the method of determ ining the temporal resolution. factor TRF at 500 Hz, 1500 Hz and 4000 Hz under free sound field conditions, as previously described by Schor n and Zwicker. The method is based on masking period patterns but meas ures only their maximum and minimum using continuous and 30-Hz square- wave amplitude modulated masking noise. The following three values of interest are measured: Threshold in quiet using interrupted continuous tones (500 ms on, 500 ms off) with the masker off; threshold masked b y a continuous masker (octave-wide continuous noise) and threshold mas ked by a rectangulary modulated masker using 14 Hz, so that periods of 72 ms and pauses of 36 ms occur. TRF was defined as the ratio between the level differences derived from the three measured values. For nor mal hearing subjects this factor is about 1. The results show signific ant variation of the TRF comparing the data of the patients with and w ithout hearing aids. The values for TRF unaided were 0.5 and 0.6 as we ll as under hearing aid. When analysing the results at all three frequ encies, in approximately 50% of the patients the TRF improved after th e fitting while in the other 50% the TRF deteriorated. Only 15 % of th e patients showed no effect. The mean values for the patients with an improvement of TRF amounted to 0.2 at 500 Hz and 0.4 at 1500 Hz and 40 00 Hz. In the patient group with a deterioration of TRF the means were 0.2 at 500 Hz and 1500 Hz and 0.3 at 4000 Hz. Factors that might infl uence the TRF during hearing aid fitting could be dependent on the ind ividual hearing or the single hearing aid. Consequently, initially the influence of the type of hearing aid was tested in some patients by f itting another aid with similar results in acceptance and speech audio metry results in free field condition with and without background nois e. These examinations yielded different variations in TRF when applyin g different hearing aids. This occurred although the IG and the speech audiometry with background noise yielded no differences between the h earing aids.