Panasonic's new technology: Using brain waves to infer the maximum volume suitable for hearing aid users

Panasonic has developed a technology that uses brain waves to estimate the maximum volume suitable for hearing aid users. The company plans to put it into production in 2015 as an automatic volume adjustment system for hearing aids.

Previously, hearing aids required "fitting", that is, adjusting the volume of each frequency of the hearing aid according to the user's hearing characteristics. The reason is that the hearing characteristics of hearing-impaired people vary from person to person, and the upper limit of the volume they can tolerate varies greatly. In the past, the upper limit was calculated based on the lower limit obtained from the hearing test, so the upper limit included errors caused by individual differences. However, since the initial volume adjustment of the hearing aid needs to be performed using this upper limit, the user will hear uncomfortable sounds, and it takes a long time to repeatedly adjust to achieve the optimal volume, which will cause a great burden on the user.

The photo shows a hearing aid being sold by Panasonic Healthcare Devices. Hearing aids are one of the company's main products.

The newly developed technology can infer the upper limit value with a high accuracy of less than ±5dB based on the brain wave change pattern of the user when listening to the test sound produced by Panasonic. According to Panasonic, the test sound is the volume level heard in daily life and it only takes about 5 minutes.

This new technology is mainly realized by two new technologies: (1) brain wave analysis technology; (2) optimal stimulation technology.

(1) The brain wave analysis technology analyzes the brain wave change pattern when the user hears a test tone (pure tones of varying volume emitted multiple times within one second) developed independently by Panasonic, thereby inferring the upper limit of the permissible volume with high accuracy. First, a test tone (continuous test tone) was developed in which the volume of a pure tone of the same frequency is decreased by 5dB in steps of 80dB (the same level as the noise inside a train) three times at intervals of 300ms.

Furthermore, by performing "wavelet analysis" (expanding the brainwave pattern in the time-frequency range) on the brainwave patterns of hearing aid users when they heard the continuous test tones, it was found that due to individual differences in the upper limit of the permissible volume, the reaction intensity of hearing aid users to the second and third test tones differed. Through the discrimination analysis of this reaction intensity, the permissible volume can be inferred with high accuracy (average error of less than ±5dB).

(2) Optimal stimulation technology In order to prevent the brain from getting used to the same stimulation, the frequency of the test sound is changed. According to Panasonic, if the same frequency sound is repeated at short intervals, the brain wave pattern will change due to habituation to the sound, and the error will increase. Therefore, the original brain wave measurement requires the interval between sounds to be extended to at least 1 second.

This time, we prepared test tones of four frequencies (500Hz, 1000Hz, 2000Hz, and 4000Hz) that are important for listening to conversations. The frequencies were determined based on the principle that the same frequency would not appear consecutively, and the test tones were sent to either ear. Therefore, even if the interval between consecutive test tones was set to about 500ms, there would be no habitual influence, and inference could be completed in a short time of about 5 minutes.

To verify the effectiveness of this technology, Panasonic has launched a clinical evaluation of hearing aid users in collaboration with the Fukui University School of Medicine since November 2011.