ASA 127th Meeting M.I.T. 1994 June 6-10

2aPP29. Measurements of distortion product phase in the cat ear canal.

P. F. Fahey

Univ. of Scranton, Scranton, PA 18510

J. B. Allen

AT&T Bell Labs., Murray Hill, NJ 07974

Amplitudes of odd-order distortion products (DPs) that are detected in animal ear canals have been used to probe cochlear health, to search for cochlear amplification, and to measure aspects of cochlear mechanical frequency response. The DP phase is also a rich source of information about cochlear mechanical response and reported here are extensive measurements of DP phase in the ear canal of cat. Much of the phase data can be explained by constant time delays that are a function of f[sub 2]. When a[sub 1] (the amplitude of the f[sub 1] primary) is greater than a[sub 2] (amplitude of the higher frequency, f[sub 2], primary), both third-order and fifth-order DPs' time delays are the same. In our preparations values are 0.6 ms at f[sub 2]>10 kHz; 0.8 ms at f[sub 2]=5 kHz; 1.3 ms at f[sub 2]=1 kHz. For the 2f[sub 1]-f[sub 2] DP, as a[sub 2] becomes greater than a[sub 1] the time delays increase, even doubling at f[sub 2]<2 kHz. The DP phase as a function of the DP frequency is generally dependent upon primary level. An interesting exception to this is that, for a[sub 1]>3a[sub 2], the phase of three DPs (2f[sub 1]-f[sub 2], 3f[sub 1]-2f[sub 2], and 2f[sub 2]-f[sub 1]) is independent of the a[sub 2] level.