The frequency selectivity of the normal and pathological human cochlea.

Human AP tuning curves (tone on tone simultaneous and forward masking curves) were measured during transtympanic electrocochleography. For subjects with near normal thresholds, average Q10 dB values (simultaneous masking) were 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Patients with threshold elevations of more than 40 dB, resulting from sensorineural hearing loss of cochlear origin, had tuning curves less sharply tuned by a factor of 2-3, with Q10 dB values of 1-2 at 2 kHz and at 4 kHz, and 1-2.3 at 8 kHz. AP tuning curves and single fibre tuning curves (frequency threshold curves) were measured in normal guinea pigs; cochlear fibre tuning is sharper than AP tuning (simultaneous masking) by a factor of 1.8 (2-20 kHz). Assuming that this factor can be applied to the human cochlea, estimates of normal human cochlear fibre Q10 dB values are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz.