Tazu Mizunami

The Statistical Distribution of Normal Hearing Thresholds for Low-Frequency Tones

The statistical distribution of normal hearing thresholds for pure tones in the low-frequency (LF) region was estimated as a function of frequency, using a similar procedure to that used in an earlier work by the authors Kurakata et al., [3]. First, the distribution of individual LF thresholds was investigated using threshold measurement data. Results indicated that the threshold variation among individuals can be approximated using a normal distribution. Second, under the assumption of normality, standard deviations (SDs) of hearing threshold distributions were calculated. For that calculation, the measurement data of different studies were integrated to enhance the estimation accuracy. Finally, using the obtained SDs, the threshold distribution around the average value was presented graphically. These results illustrate the profile of our auditory sensitivity at LFs more accurately and are useful for evaluating the audibility of LF noises because they incorporate individual differences.

Effect of Ageing on Hearing Thresholds in the Low Frequency Region

The hearing threshold for low frequency (LF) tones was measured in a pressure field to investigate the effects of ageing on hearing sensitivity. Participants were young adults around 20 years old and older adults over 60. Measurement results showed that the older listeners had a higher threshold, on average, than the young listeners. The difference of median thresholds between these two groups was about 10 dB at every measurement frequency. Furthermore, hearing abnormalities other than age-related hearing loss showed no great effect upon the LF thresholds. Comparison of LF thresholds and audiograms (i.e. mid and high frequency hearing) of the older listeners revealed only moderate correlation between them. These results suggest that older people retain good hearing sensitivity in the LF region, in contrast to their often-degraded sensitivity at higher frequencies. Therefore, in LF noise evaluation, we should carefully regard the possibility that older listeners can perceive a low level LF noise.

Auditory signals for consumer electronics: Accessible-design approach and international standardization

Auditory signals are often used in human-machine interface of consumer electronics. Those signals are expected to improve the usability and accessibility of such products. This paper reviews accessibility-related standards on auditory signals for consumer products that were established by the Japan Industrial Standards Committee and are being drafted in a Technical Committee of the International Organization for Standardization, ISO/TC 159 “Ergonomics”.