On the Limitations of Cochlear-Microphonic Measurements

The interelectrode phase and the relative microphonic magnitude have been measured from electrodes placed in scalae vestibuli and tympani of the first three turns of the guinea pig cochlea. The relative phase difference between two electrodes in a given turn appears to be a sensitive indicator of the contributions to the recorded microphonics of local and remote potential generators. It is suggested that in the guinea pig, local responses can be measured up to 10 000 Hz in the first turn, up to 3000 Hz in the second turn, and only up to 500 Hz in the third turn. The results of interaction between local and remote activity, as manifested in amplitude and phase patterns of the microphonic, are demonstrated in detail and the influence of stimulus intensity is treated. Attention is called to some of the pitfalls that result from drawing inferences from data that are obtained in a frequency region where the response is dominated by remote components. Finally, for comparison, interelectrode phase data are given for the first turn of the cat’s cochlea, and the problems of recording from the round-window region are considered for both cat and guinea pig.