Can We Apply Ultrasound to Hearing Aids for the Profoundly Deaf?
There has been considerable debate concerning bone-conduction ultrasound audibility. Although several hypotheses predicting the peripheral mechanisms of ultrasound perception have been proposed, there was no report regarding the central mechanisms of ultrasound perception,i.e., which sensory area in the brain is activated by ultrasound stimulation, the auditory area, the somatosensory area or a special area for ultrasound perception, before our report. We reported, for the first time, that the auditory cortex is activated by ultrasound stimulation, not only in normal-hearing persons but also in some profoundly deaf subjects who cannot sense any non-ultrasound at all with magnetoencephalography. Furthermore, we showed that ultrasound modulated by speech /a/ and /i/ significantly elicited mismatch magnetic fields (MMF) within the auditory cortex, which have been known as neural activities reflecting the detection of acoustic differences among stimuli even for profoundly deaf subjects. It proves the possibility of transmitting speech information to the auditory cortex of the profoundly deaf through modulated ultrasound stimulation, hence ultrasound could become an effective communication tool for the profoundly deaf without any surgery like cochlear implants.
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