ACOUSTIC DISTORTION AS A MEASURE OF FREQUENCY-SELECTIVITY - RELATION TO PSYCHOPHYSICAL EQUIVALENT RECTANGULAR BANDWIDTH

The magnitude of cubic intermodulation distortion generated when two t ones are progressively separated in frequency reaches a broad maximum when the distortion frequency falls just over half an octave below the high-frequency stimulus (f2), when this distortion is measured with a microphone in the ear canal. For the component 2f1-f2, this peak occu rs at an f2/f1 ratio of approximately 1.2. The tuning, magnitude, and mean group delay of this distortion peak was measured for a fixed f2 o f 4 kHz at 40 dB SPL and a varied f1 at 55 dB SPL in eight human subje cts with normal hearing. The distortion peak measures were compared wi th the frequency selectivity at 4 kHz of the same eight subjects deriv ed using a forward-masking notched-noise paradigm. In the six subjects from whom good, repeatable levels of distortion were measured, a sign ificant negative correlation was found between the tuning of the disto rtion peak and the psychophysical bandwidth at f2. It is concluded tha t the tuning of the distortion peak may provide an objective measure o f frequency selectivity in the human cochlea.