The hearing aid benefit might be influenced by transient distortion produced by hearing aid systems. However, distortion measurements have rarely been made at use-gain settings. And currently there is no standardized method for measuring transient distortion in hearing aids. In this study, transient distortion was described as the power level of time response measured in ear canals. And skewness was defined for quantifying transient distortion. Transient distortion was evaluated using four kinds of earmold material (hard, soft, silicone, and sponge). No significant differences in time response were seen among hard, soft, and silicone earmols. The differences in skewness between a sponge earmold and a hard earmold were statistically significant at the .01 level. This results suggested that transient distortion might be reduced by using a sponge earmold. In a digital hearing aid with minimal transient distortion, the gain was reduced quickly when loud sounds occurred, and the gain was increased after loud sounds diminished.
A new method of hearing aid fitting was performed by adapting input level 65dBSPL whitch was suitable for speech level, to MCL, and input level 90dBSPL suitable for maximum out put level, to within UCL. Expected MCL and UCL were immediately measured and decided, by using insert earphone and SPL meter, so no more re-adjustment of hearing aid's responses was needed, in 96% of analog type hearing aids with gain controller, and even in 87% of digital type hearing aids without gain controller.
In 7 persons with deafness who use conventional hearing aids (analog or programmable type), digital hearing aids of 5 models (in the ear type or behind the ear type of Danalogic: 163D, Digitarian: HI-D2, Resound: ED5, Siemens: PRISMA, SENSO: C9) were used in each for two weeks. Speech perception ability and subjective evaluation were investigated, and effectiveness of the digital hearing aids was analyzed. All persons had evaluated the digital hearing aid not a few. When speech perception ability with the digital hearing aids was compared with that of conventional hearing aids, the average of 7 persons was 90.3% and 85.1% respectively without noise, 65.4% and 50.3% at S/N ratio +5dB under noise, 38.3% and 57.1% at 0dB, and 28.0% and 44.5 at -5dB. And there was the improvement of specch perception ability by the digital hearing aid. In conclusion, there was some improvement by the digital hearing aid in all cases under noise. The results of the average of speech perception ability using digital hearing aid were better than those using conventional hearing aids, and especially, it was clear that the speech perception ability showed the improvement under noise.
In 48 patients who had a moderate hearing impairment and were fitted hearing aid in our department, aided thresholds and word discrimination test at the final hearing aid setting were measured by a new procedure of sound-field measurement with a head-worn small speaker (Virtual Phone, SONY). The average aided thresholds were about 30dBnHL at 250-2000Hz. Those were same as our initial targets of hearing aid fitting. The average functional gain was most similar to POGO method in three prescriptive methods; the gain for 30dBnHL of desired aided level, NAL-R and POGO. The patients with good discrimination showed flat contour of 30dBnHL at 250-2000Hz in aided thresholds, whereas, the patients with poor discrimination had higher thresholds at 250 and 500Hz. We considered that the flat aided thresholds of 30dBnHL is valid target for hearing aid fitting.
To estimate the optimum loudness for obtaining maximum speech recognition score, we carried out speech discrimination test on 124 ears with sensorineural hearing loss by the use of 67-S monosyllable list. Every time just after one list was tested each subject was asked to evaluate the loudness of the test speech sound using seven steps categorical scale. As an index of optimum speech loudness, the ratio of the ears was calculated in which the maximum recognition score within 5% was obtained at the speech level with the every loudness category. The ratio showed maximum at the category 5 (“comfortable, but slightly loud”), but there was no significant difference in the ratio between category 5 and category 4 (“comfortable”) or 6 (“loud”). Comparison by the type of auioram showed that the same results were obtained in each type group of audioram, and in the group of low tone hearing loss type audioram the ratio was higher at the levels with low loudness rating (2: “soft” or 3: “comfortable, but slightly soft”) than in the groups of flat type or higr-tone hearing loss type audiogramn.
It is known that the pitch of the absent frequency in the input signals such as complex tones can be perceived, and it is called the phenomenon of the missing fundamental. It is thought that place and temporal information, which play an important role in pitch perception, are integrated at the central auditory system. However, the interaction between residue pitch which does not have place information and pure tone perception has not been reported. To investigate the interaction between residue pitch and pure-tone perception, using the randomized maximum likelihood sequential procedure, we examined the threshold shifts of tone bursts by the masker of the filtered click train, which provides the phenomenon of the missing fundamental. The results showed the narrow masking patterns by the filtered click train compared with those by the pure tone or the band noise. When the level of the masker was high, a broad threshold elevation was added. The masking effects decreased with the elevation of the high-pass cut-off frequency of the filtered click train.