Longitudinal distribution of the cochlear microphonics inside the cochlear duct (guinea pig).

Cochlear microphonics (CM) were recorded with glass micropipet electrodes inserted in the scala media in the four turns of the guinea pig's cochlea. From the data acquired, the longitudinal distribution of the cochlear microphonics were determined. The points of maximum sensitivity for different frequencies along the cochlear partition were 2 mm apart for a change of 1 oct. By increasing the intensity of the stimuli, there was a shift of 4 mm of the point of maximum voltage of the CM toward the base of the cochlea. The slope of the proximal side of the envelope was steeper than that of the distal side. Both proximal and distal slopes doubled their magnitude for a change from 300 to 3000 Hz. At moderate sound‐pressure levels (i.e., 70 dB), the voltages of the CM were the same for all frequencies at the point of maximum stimulation.