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1.1 Basilar membrane mechanics as the basis of inner ear function
The function of the hearing organ ha been based mainly on the basilar membrane mechanics because it is the only
structure accessable from the outside and therefore has been measured extensively Bekesy,1960; Johnstone & Boyle,
1967; Rhode, 1971, 1980; Sellick et a!. 1982; Robles et aL, 1986). Although the organ of Corti consists of a complex
and highly organized arrangement of sensory cells, the role of individual cells in mechanical analysis of the auditory
stimuli was not known.
1.2 The avialable measuring techniques not suitable for cellular vibration measurements
The basilar membrane vibrations were measured with (i) capacitive probe (Wilson & Johnstone, 1972); (ii) homodyne
interferometry (Khanna & Leonard, 1982); and (iii) Mossbauer method (Johnstone & Boyle, 1967; Rhode, 1971). The
first technique required the placement of the probe close to the surface to be measured while the other two techniques
required the placement of an optical reflector or radioactive foil on the structure to be measured. In order to place the
foil on a cell the overlying cells or structures would have to be removed, seriously compromising the integrity of the
cochlea and altering its response.
1.3 Need for cellular vibration measurement
Correlations made between the basilar membrane tuning and the outer hair cell condition suggested that the outer hair
cells may be directly involved in the mechanical tuning of the cochlea (Khanna & Leonard, 1982, 1986 a, b). These
results provided the inspiration to build a non-invasive optical vibration measuring system with which the mechanical
response of individual cells could be measured in an intact organ.
1.4 Organization of ITER
It became quite clear about ten years ago that state of the art technology in several fields was needed to design and
build the necessary measuring instrument and to fully exploit its potential. An international team of experts from
several fields of science were therefore invited to help design the instrument and to carry out the cellular
measurements with it. This International Team for Ear Research is called ITER. A preliminary report of our progress
has been published (ITER, 1989).
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