Frequency‐position maps for the chinchilla cochlea

Frequencies of tones are mapped on to distances along the organ of Corti by associating behaviorally measured threshold shifts with areas of histologically observed damage. Individual differences in the lengths of the cochleas are normalized by expressing distance in percentage of the total length and then converting to a standard length of 18.4 min. Useful points from at least 17 ears studied at CID along with similar data of Ryan and Dallos collected at Northwestern University are used to construct the map. It appears that distance in mm plotted against log frequency can be approximated by locating 1.6 kHz at the middle of the basilar membrane and moving about 2.5 mm for each octave change in frequency. In contrast to the familar maps of cat and man, there is a suggestion that the slope (mm/log/f) is greater in the apical half and less in the basal half of the cochlea. [Supported by NS 03856 and NS 01791.]