高周波聴力の左右差 : 一側性の蝸牛障害の評価への応用

High-frequency audiometry has the potential to detect hearing impairment at its early stage. However, several problems prevent the clinical application of high-frequency audiometry. In this study, the dispersion and left-right difference in the high-frequency sensitivity were investigated in normal hearing volunteers. In our results, the difference between the left and right ears varied only slightly among individuals or age groups, while dispersion of hearing threshold values became marked with an increase in frequency. The results suggest that the measurement of left-right difference in high-frequency sensitivity may be useful for the evaluation of unilateral impairment. To investigate this usefulness, the left-right differences were measured in the patients complaining of unilateral cochlear symptom with normal hearing. Considering the results of normal hearing, we determined that abnormal left-right difference in high-frequency sensitivity was over 20 dB. In 12 patients with unilateral tinnitus, 7 showed left-right differences, and 6 had tinnitus in the ear with increased thresholds. Our results suggested a relationship between tinnitus with normal hearing and hearing impairment in the high-frequency range.博士（医学）・乙1335号・平成26年3月17

Magnetoencephalographic study on forward suppression by ipsilateral, contralateral, and binaural maskers.

When two tones are presented in a short time interval, the response to the second tone is suppressed. This phenomenon is referred to as forward suppression. To address the effect of the masker laterality on forward suppression, magnetoencephalographic responses were investigated for eight subjects with normal hearing when the preceding maskers were presented ipsilaterally, contralaterally, and binaurally. We employed three masker intensity conditions: the ipsilateral-strong, left-right-balanced, and contralateral-strong conditions. Regarding the responses to the maskers without signal, the N1m amplitude evoked by the left and binaural maskers was significantly larger than that evoked by the right masker for the left-strong and left-right-balanced conditions. No significant difference was observed for the right-strong condition. Regarding the subsequent N1m amplitudes, they were attenuated by the presence of the left, binaural, and right maskers for all conditions. For the left- and right-strong conditions, the subsequent N1m amplitude in the presence of the left masker was smaller than those of the binaural and right maskers. No difference was observed between the binaural and right masker presentation. For left-right-balanced condition, the subsequent N1m amplitude decreased in the presence of the right, binaural, and left maskers in that order. If the preceding activity reflected the ability to suppress the subsequent activity, the forward suppression by the left masker would be superior to that by the right masker for the left-strong and left-right-balanced conditions. Furthermore, the forward suppression by the binaural masker would be expected to be superior to that by the left masker owing to additional afferent activity from the right ear. Thus, the current results suggest that the forward suppression by ipsilateral maskers is superior to that by contralateral maskers although both maskers evoked the N1m amplitudes to the same degree. Additional masker at the contralateral ear can attenuate the forward suppression by the ipsilateral masker

Suppression of Subsequent N1m Amplitude When the Masker Frequency is Different from the Signal

When two tones are presented in a short interval of time, the presentation of the preceding tone (masker) suppresses the response evoked by the subsequent tone (signal). To address the processing in forward suppression, we applied 2- and 4-kHz maskers, followed by a 1-kHz signal at varying signal delays (0 to 320 ms) and measured the signal-evoked N1m. A two-way analysis of variance revealed a statistically significant effect for signal delay in both masker presentation conditions. The N1m peak amplitude at the signal delay of 320 ms was significantly larger than those of 10, 20, 40, and 80 ms ( p < 0.05). No significant enhancement for the very short signal delay was observed. The results suggest that the enhancement of N1m peak amplitude for short signal delay conditions is maximized when the frequency of the masker is identical to that of the signal

Mean N1m amplitudes normalized to the amplitude evoked by the signal without masker in three masker intensity conditions.

<p>The upper (a) and lower (b) graphs show the respective values before and after subtracting the masker response. The error bars indicate standard errors.</p

Schema of the seven stimulus sets.

<p>The presentations in the right (R) and left (L) ears are separately illustrated. The solid and open trapezoids indicate the masker and signal presence, respectively.</p

Mean N1m amplitudes evoked by three maskers without signal in three intensity conditions.

<p>The error bars indicate standard errors. Because the N1m amplitudes were normalized to those evoked by the left masker without signal in each intensity condition, the standard errors for the left masker without signal resulted in zero.</p

Word Categorization of Vowel Durational Changes in Speech-Modulated Bone-Conducted Ultrasound

Ultrasound can deliver speech information when it is amplitude-modulated with speech and presented via bone conduction. This speech-modulated bone-conducted ultrasound (SM-BCU) can also transmit prosodic information. However, there is insufficient research on the recognition of vowel duration in SM-BCU. The aim of this study was to investigate the categorization of vowel durational changes in SM-BCU using a behavioral test. Eight Japanese-speaking participants with normal hearing participated in a forced-choice behavioral task to discriminate between “hato” (pigeon) and “haato” (heart). Speech signal stimuli were presented in seven duration grades from 220 ms to 340 ms. The threshold at which 50% of responses were “haato” was calculated and compared for air-conducted audible sound (ACAS) and SM-BCU. The boundary width was also evaluated. Although the SM-BCU threshold (mean: 274.6 ms) was significantly longer than the ACAS threshold (mean: 269.6 ms), there were no differences in boundary width. These results suggest that SM-BCU can deliver prosodic information about vowel duration with a similar difference limen to that of ACAS in normal hearing