Deafness is the most prevalent sensory disability across nations. The sense of hearing has been least understood owing to the challenge in accessing the inner ear deeply positioned inside the head. In addition to the challenging physiological environment, experiments in the live mammalian cochlea continue to demand better methods and innovative sensors. Our long term goal is to develop better understanding and effective diagnosis of hearing loss by developing novel instrumentation geared towards live intra-cochlear measurements, as well as to develop better understanding of the active vibro-acoustics in the inner ear using computational modeling.
Computational modeling of sound processing in the human ear
Sound entering the outer ear vibrates the middle ear bones and launches vibroacoustic waves inside the inner ear organ, cochlea. Complex processing of sound inside the cochlea eventually leads to signals that provide input to the auditory nerve.
In our 2007 JASA paper, titled "A mechano-electrical-acoustic model of the cochlea: response to acoustic excitation", we developed a multi-scale model of the cochlea integrating mechanical, electrical, and acoustic domains. This 'MEA' model is able to predict the data obtained from several physiological experiments in live guinea pig cochlea. A description of the MEA model can be seen in the "Past work" tab.
In our recent publication in 2020, we showed that there is a fine balance between the local electromechanical and vibroacoustic properties of the cochlea, and that this balance is important for the active feedback amplification of low level sounds processed by our ear. The relevant journal publication is:
Agarwal, N., and Ramamoorthy, S., “Balance in the feedback loop components of the mammalian cochlear amplifier.”, Journal of Applied Physics, 128(3), 034701, 2020.
We are now integrating nonlinear mechanics of the cochlea into the MEA model and combining it with a model for the middle and outer ear to predict otoacoustic emissions in humans. The relevant conference abstract is:
Agarwal, N., and Ramamoorthy, S., “Investigation of distortion product otoacoustic emissions in humans using a nonlinear mechano-electro-acoustic model of the cochlea.”, Journal of the Acoustical Society of America 149(4), A76-A76, 2021.
Development of new sensors for auditory research experiments
We are developing new sensors and methods for auditory research experiments. Our first sensor for this purpose is built upon optical coherence tomography (OCT). Using OCT, we have developed a sensor for simultaneous measurement of the velocity of a vibrating structure and the fluid pressure in the vicinity of the structure. To the best of our knowledge, there is no alternative method in the literature for simultaneous vibration and pressure detection. Spectral-domain OCT can simultaneously measure the vibrations of multi-layered structures in the axial direction (that is along the OCT light). By inserting a designed miniature vibroacoustic sensor whose diaphragm is placed in the vicinity of the vibrating diaphragm of interest and measuring the vibrations of both diaphragms simultaneously using spectral-domain OCT, the proposed method is demonstrated. This measurement method therefore provides simultaneous measurement of both velocity and pressure inside any micro-channel, including the mammalian cochlea as illustrated in the right panel.
The sensor is described in the following journal publication:
Ramdas, R., Agarwal, N., Atpadikar, M., and Ramamoorthy, S., “Simultaneous measurement of vibration and pressure in vibroacoustic microchannels.” Applied Acoustics, 169, 107489, 2020.