This study estimated the mechanical response of the cochlea to pulsati
le electrical stimulation of the scala tympani of the cat. The auditor
y nerve compound action potential evoked by an acoustic probe was forw
ard-masked by a train of charge-balanced biphasic current pulses. Mask
ing as a function of probe frequency reflected the excitation pattern
of the response to the masker and resembled the spectrum of the electr
ical stimulus. Both pulse rate and pulse width influenced the degree o
f masking. The vibration of a region of the basilar membrane was estim
ated by recording the local cochlear microphonic evoked by biphasic pu
lses. The amplitude of the cochlear microphonic was proportional to th
e amplitude of the spectral component of the electrical stimulus to wh
ich the local cochlear microphonic was tuned. These results are consis
tent with the generation of a mechanical response to the electrical st
imulus.