A objective measurement system to investigate temporal characteristic of the auditory sense using ABR was developed. This system was evaluated from the experimental results in normal subjects. How the forward masking phenomenon by white noise reflects to ABR was observed. In the experiments, changes of ABR of a probe tone was measured as functions of the duration of masker and a time difference between masker and probe tones. From experimental results, the latency of a waveform of each component of ABR increased as the duration of masker increased. This result corresponded to the phenomenon that latency increases as the intensity of the click stimulation decreases. An influence of masker on the amplitude of ABR was hardly appeared at 15msec after masker stimulation. These results were in accordance with the previous research results. This measurement system will be useful to investigate the temporal characteristics of the auditory brainstem response.
It is difficult to obtain sufficient speech articulation even if the amplified sound is given to the sensory-neural hearing impaired persons. It is conceivable that one of the reasons is that the temporal resolution of the auditory sense is low. In this paper, the temporal resolution of two short sounds and a temporal masking characteristic were investigated, targeting the hearing impaired students who belonged to the school for the deaf. As a result, an auditory image that was produced by a short sound could be apporoximated with a normal distribution function and a forward masking curve could be apporoximated with the exponential function. The temporal characteristic of the auditory sense was evaluated by using parameters of these functions and the parameters were compared with those of the normal hearing listeners. Although the 2-sound temporal resolution of the hearing impaired was almost the same as that of the normal listeners, the range of forward masking of the hearing impaired spreaded 3-4 times compared with normal persons. As for the range of backward masking, there was no difference from normal persons. How to design the hearing aid for the sensoryneural hearing impaired was discussed on the basis of these results.
Using the Warren type experimental method, we required the subjects to determine the order in a sequence of four vowels (a; iv; u; e) repeated continuously without pause. The duration of each vowel segment was varied from 70 to 500msec, and the vowel order was randomized for each duration value. The results were as follows: 1. As a scoring method, the 24-point method in which the scoring is based on each vowel is more useful from a clinical point of view than is the 6-point method in which the scoring is based on one sequence unit since the former has a smaller rejection limit. 2. The critical rates for identification (90% correct level) were obtained as 8items/sec. (16bits/sec.) in young adults and as 4items/sec. (8bits/sec.) in healthy elderly individuals. As the duration of each vowel seqment became shorter, the information processing rate decreased to a half gain in olderly individuals. This phenomenon shows that the speed of conversation is very important for olderly individuals who use hearing aids. 3. The relation between the ability to count interrupted tones and the critical rates for identification, which were both measured at the same time, showed a significant correlation. This indicates the possibility that they partially share common mechanisms in the central nervous system. 4. The tendencies in hearing the vowel segments was discussed. 5. This experimental method is useful for the differential diagnosis of retrocochlear lesions and for an evaluation of hearing acuity in elderly individuals.
The correlation between the head size of 75 normally hearing adults and the latency of their auditory brainstem responses was investigated. Positive correlations were obtained between the head size and absolute latencies of wave III, V and the I-V interpeak latency. However, no correlations were obtained between the head size and the latency when separating sexes. The rank correlation analysis for male versus famale subjects produced significantly shorter latencies for female for both wave III and V absolute latency and I-V IPL. These analyses suggest that ABR norms should be developed separately for males and females, and that head size is not the only factor accounting for differences between the sexes in ABR latencies.
Auditory steady state responses elicited with sinusoidally amplitude-modulated tones of 0.5 to 4kHz were recorded in 9 adult subjects with normal hearing. The magnitude of the responses was greatest at 40-Hz modulation rate and at 90% modulation depth. The magnitude tended to decrease as a function of stimulus frequency. The lapse of time was measured from the minus peak of the amplitude-modulated tones to the following positive peak of the responses at the active electrode placed on the forehead just beneath the hairline. Its approximate values ranged between 12 and 15ms. The mean latency of the responses measured following Diamond Method was 12.2ms. A significant effect of sleep was found in the responses. The magnitude of the responses in deep sleep state frequently decreased less than 1/3 of that in awake state.
The purpose of this study was to provide the methodology how to use speech discrimination test (57-words list by Japan Audiological Society), and its usefulness for the fitting of hearing aids was evaluated. Speech discrimination score of 163 sensorineural hearing-impaired patients with/without hearing aids were mesured by means of speaker methods, and the results were analysed. The results were 1) When speech discrimination score with hearing aids is 10% lower than the score obtained without hearing aids, it is considered that the patient requires refitting of the hearing aids. 2) The improvement of consonants by hearing aids was varified according to the degree of discrimination score without hearing aid in the hearing-impaired. It is possible to predict that the consonant and vowel can be improved by fitting hearing aids after the speech discrimination score of respective subjects is evaluated. 3) Credibility of speech discrimination score without hearing aids increases if this is measured again and compaired with discrimination score with hearing aids obtained 2 months after the initial discrimination score of tained without hearing aids. From this study, it was found that upon comparative measurement of speech discrimination score with/without hearing aids of individual cases, the use of speech discrimination test is usefull for considering the adaptability of hearing aids.
Brain electrical mappings of ABR components by latency measurement were studied in cats. Topographic mappngs of the scalp were made by two methods. In the first one, the latency was measured from the base line which was the middle line between the fastest latency and the slowest latency in 16 electrodes on the scalp of normal cats. It was called “Base Line Method”. The other is called as SPM (Significance probability mapping) Method, reported by Duffy in 1981 in his lesion experiments. The lesions were experimentally made by pentobarbital, anoxia, freezing the inferior colliculus. The results were as follows. 1) Mappings by Base Line Method did not clearly show the changes on the scalp, when ABR were recorded by the sampling time of 50μ seconds in normal cats. 2) Mappings by SPM Method were better than mappings by Base Line Method to show very small changes of the latency distribution on the scalp. 3) The continuous discrepancy between the mappings by the administration of pentobarbital and anoxia was similar, but it was deffered with modality mappings following freezing the inferior colliculus. 4) SPM Method is acceptable for the demonstration of continuous discrepancy of the mapping.