Comment on “modulation of the hair cell motor: A possible source of odd-order distortion”

This reply to the response by Brown [J. Acoust. Soc. Am. 96, 2210-2215 (1994) on the report “Intermodulation distortion (F2Fx) in inner hair cell and basilar membrane responses [J. Acoust. Soc. Am. 93, 2061-2068 (1993)]” by Nuttall and Dolan is for the purpose of adding additional data concerning the nature and origin of the round window (RW)-recorded quadratic distortion tone (QDT) signal. It is shown that a major portion of the RW electrical signal originates from the activity of auditory neurons since tetrodotoxin (TTX) applied to the cochlea diminishes the distortion product by about 75%. The neural component is also responsible for the characteristic 900-Hz optimal frequency separation of the primaries in producing the response. These data support our earlier suggestion [Nuttall and Dolan, J. Acoust. Soc. Am. 93, 2061-2068 (1993)] that the level of intracellular receptor potential at the QDT frequency would be a stimulus for afferent fibers at low sound levels. These new data do not force a reinterpretation of Brown's hypothesis on the relationship of quadratic and cubic intermodulation distortion.