Investigation of Frequency-Selective Loudness Reduction and Its Recovery Method in Hearables

With the ongoing spread and functional improvement of hearables, we may soon find ourselves in a society where users are wearing hearables at all times. In a hearable environment of this kind, the constant presentation of aural information to users may impede their ability to hear external noises that require their attention. For example, suppose the constant presentation of information in a particular frequency band causes a reduction in the subjective perception of sound pressure (loudness) of the corresponding frequency band. In such a case, the response to environmental sounds that indicate danger (e.g., the sound of an approaching car or an emergency alarm) may be delayed, leading to potential disaster. In this study, we investigated 1) how the presentation of a sound of a specific frequency through a hearable affects the loudness; and 2) which stimulus sound is most effective for recovering the decrease in loudness. In the first investigation, a loudspeaker presented the sound of a specific frequency that imitates environmental sound, and a hearable gave a stimulus sound of a particular frequency based on the frequency of the loudspeaker sound. The results showed that the loudness decreased by more than 10.0% in all stimulus sounds listened to with hearables, and the amount of the decrease tended to be larger the closer the frequency of the loudspeaker sound was to that of the hearable sound. In the second investigation, we hypothesized that the presence of specific recovery stimulus sounds would be effective in quickly restoring any loudness that had decreased, and the results showed that the amount of recovery was greater for all the recovery stimulus sounds we used compared to when the stimulus sounds were not presented.