Comparison of sound-transmission and cochlear-microphonic characteristics in Mongolian gerbil and guinea pig

Abstract

Characteristics of cochlear microphonic (CM) of guinea pigs, when compensated for electrical capacitive shunting within the cochlea, parallel corresponding mechanical characteristics. Specifically, good agreement is found for the middle‐ear transfer characteristic, basilar‐membrane phase, and cochlear travel times. CM corrections derived from guinea‐pig experiments have been extrapolated to CM recorded in Mongolian gerbils to obtain estimates of middle‐ear and basilar‐membrane characteristics, a cochlear frequency map, and cochlear travel times for both animals. The estimates indicate that basilar‐membrane tuning curves are almost symmetrical in the apical turn. Model experiments suggest that the apparent sharpening of the low‐frequency leg of these curves is produced by a shunting effect of the helicotrema. Comparisons are also made among results obtained with three different electrode configurations: a single electrode in scala media (SM), a differential pair in scalae media and tympani (SM–ST), and a differential pair in scalae vestibuli and tympani (SV–ST). Results from both guinea pigs and gerbils indicate a slight advantage in the SM–ST configuration.