Figure 1.

Validation of high-speed imaging and hair bundle stimulation techniques. A, High-speed imaging of an actuated flexible fiber at 50,000 frames per second (black traces) and the classical photodiode technique (blue, semitransparent) yielded similar results in fiber displacement. An expansion of the onset of the fiber displacement showed an oscillation of ∼9 kHz with both techniques. The piezo stimulus was low-pass filtered at 10 kHz. B, Image of a P9 rat OHC hair bundle is shown with a passive flexible fiber in view to serve as a readout of the force applied by the fluid jet. Colored lines indicate where motion was measured. C, In a single stimulation protocol, we monitored the fluid-jet force with the flexible fiber displacement (red, semitransparent), and we measured hair bundle displacement (gray). The hair bundle has a continued movement in the direction of the stimulation (i.e., mechanical creep, highlighted in one trace in black) even when the force from the fluid jet was step-like. M indicates the fluid-jet stimulus voltage waveform, which was low-pass filtered at 1 kHz. D, A time expansion of the onset of the fiber and hair bundle displacements from C shows the short rise time of the force step. The stimulus waveform (M, delayed and normalized) is overlaid in black to show that the stimulus voltage waveform kinetics match the force output. E, The fiber displacement plotted against the stimulus voltage indicates linearity within the stimulus range used. F, From the experiment in C, the resulting MET current at −84 mV holding potential shows the presence of slow-current decay and the absence of fast-current decay. Scale bars, 2 μm.