Human frequency-following response correlates of the distortion product at 2F1-F2.

We characterized the 2F1-F2 distortion product reflected in the human frequency-following response (FFR). In the first experiment, we evaluated the input-output growth functions of the distortion product at 2F1-F2 (FFR-DP) for three primary pairs. In the second experiment, we tested the effect of primary tone level variation on the FFR-DP. The results for all three stimulus pairs showed that while the amplitude of FFR-DP increased with stimulus intensity, the slope of the amplitude growth decreased with increasing frequency. Consistent with distortion product otoacoustic emission (DPOAE) data, our observations suggest that there is a distinct region where the separation of the primary tone levels produces maximal distortion. The robust FFR-DP measure could complement the less reliable DPOAE at low frequencies and when middle ear pathology precludes its measurement.