11.4.3 Comparison of Pre- and Post-mortem Response of the TM in the Frequency Domain FFT analyses were performed on the displacement waveforms at each point on the TM surface to define maps of the displacement magnitude, as shown in Fig. 11.6, at the frequencies with prominent spectral peaks obtained from the mean of the FFTs, as marked by circles in Fig. 11.7. After analysis of the results, the following was observed: • The displacement maps show more spatially complex shapes with lower amplitudes in the in-vivo condition. • The similarities of the frequencies of peak displacements in pre- and post mortem conditions suggest minimal changes in the mass and stiffness of the middle ear. Fig. 11.4 In-vivo measurement results up to 1.8 ms; (a) mean (N¼6) displacement maps taken at eight temporal instances between 143 and 1500μs. The color bar codes instantaneous displacements between 0.1μm/V. The map at 143μs shows the umbo peak motion and the numbers and arrows indicate six locations where displacement versus time waveforms are plotted in (b). Point-1 is at the umbo, and the manubrium is outlined in black; (b) displacement waveforms at six locations normalized by the stimulus voltage are illustrated. At each location, six individual measurements at two different stimulus voltages (T1-3: 2 V and T4-6: 3 V) are plotted together with the corresponding mean, shown by open diamond. The sound pressure waveform recorded by the microphone is shown in green in the panel of point-2 11 High-Speed Holography for In-Vivo Measurement of Acoustically Induced Motions of Mammalian Tympanic Membrane 79
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