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.