Figure 2.

Analysis of a typical response to mechanical stimulation of an active hair bundle. (A) The fiber’s base motion, X_B(t), reflected ±10-nm sinusoidal stimulation at 9 Hz, a frequency below the cell’s characteristic frequency of 14 Hz. (B) The fiber’s tip motion, X(t), was more than double the magnitude of stimulation and exhibited a phase lead. (C) The viscous drag force, F_D(t), continuously opposed hair-bundle motion. (D) Because viscous dissipation continuously withdrew energy from the hair bundle, the instantaneous viscous-drag power, P_D(t), was negative. (E) The elastic force exerted by the stimulus fiber on the hair bundle, F_SF(t), was dominated by the bundle’s elastic reactance. (F) The power provided by the stimulus fiber, P_SF(t), was greatest during the fast components of the fiber’s tip motion. The fiber resisted negatively directed hair-bundle movement but powered motion in the opposite direction. Each record, the average of 21 cycles of oscillation, has been duplicated to emphasize its periodic features; the vertical lines facilitate comparison of response phases.