FIG. 1.

Left panel: Bottom image: scanning electron microscope image of a stereociliary bundle, in a top-down view. Top image: optical image of a glass fiber attached to the row of tallest stereocilia. The space bars in both images denote 1 μm. Right panel: Mode-locking at a drive amplitude of 20 nm. Bottom trace: spontaneous oscillations of a free stereociliary bundle. Middle trace: spontaneous oscillations of a stereociliary bundle with an elastic glass probe attached to its tip with a stiffness of 100 μN/m with no imposed deflection. Top trace: sinusoidal deflections are imposed on the bundle with a 20 nm amplitude and with increasing frequency from 17 to 23 Hz (red trace). The displacement of the base of the probe is shown overlaid in black, which has been arbitrarily scaled for visibility. Frequency increases by 1 Hz every ten cycles. Decades of drive cycles are indicated by vertical dashed lines. Events of phase slip between bundle and probe are indicated by arrows. The magnified portion shows a “phase-slip” event.