Modern methods for measurement of basilar membrane displacements

Basilar membrane displacements in response to sound at threshold intensities are in the fractional Angstrom range. Visual measurements, as used by Bekesy in his pioneering studies, are by definition limited to values above 10 000 A. The present paper discusses a number of modern techniques capable of taking measurements at lower Anstrom levels: One-point methods (capacitive probe, Mossbauer effect, laser interferometry, and optical heterodyne spectroscopy) and pattern-assessing methods (time-averaged and real-time holography). Advantages and disadvantages of these methods are being discussed.