Figure 6.

Modeling of hair-bundle movements. (a) Simulations of the thermal movements expected for stereocilia in a series-parallel hair-bundle configuration, with the two indicated values of gating-spring stiffness, yield cross-correlations much lower than those observed experimentally. (b) The coherency spectrum obtained for a gating-spring stiffness of 1,000 μN·m⁻¹ shows a nearly flat coherence near 0.2 and an essentially random phase for nearly all frequencies. This behavior, which is characteristic of finite samples of independent random processes, implies negligible coupling between stereocilia. (c) Even for an unrealistically large value of the gating-spring stiffness, 53,000 μN·m⁻¹, the coherency spectrum for a series-parallel model displays results very different from those observed experimentally. The averaged coherence lies below 0.8 for all frequencies exceeding 500 Hz and reaches the value expected for independent random processes around 1 kHz; the phase becomes nearly random above the latter frequency.