Viscoelasticity in the ear's mechanoelectrical-transduction apparatus
The ear detects sounds so faint that they produce only atomic-scale displacements in the mechanoelectrical transducer, yet thermal noise causes fluctuations larger by an order of magnitude. Explaining how hearing can operate when the magnitude of the noise greatly exceeds that of the signal requires an understanding both of the transducer's micromechanics and of the associated noise. Using microrheology, we characterized the statistics of this noise; exploiting the fluctuation-dissipation theorem, we determined the associated micromechanics. The statistics revealed unusual Brownian motion in which the mean-square displacement increases as a fractional power of time, indicating that the mechanisms governing energy dissipation are related to those of energy storage. Although this anomalous scaling contradicts the canonical model of mechanoelectrical transduction, the results can be explained if the micromechanics incorporates the viscoelasticity characteristic of biopolymers. We amended the canonical model and demonstrate several consequences of viscoelasticity for sensory coding.