Electric Responses of the Guinea Pig Ear to High Audio Frequencies

¹ From the Central Institute for the Deaf, St. Louis, Missouri

Cochlear microphonic (CM), action potentials (AP), and summating potential (SP) were recorded from the round windows of anesthetized guinea pigs in response to tone bursts that had nearly linear rise and fall of 1.0 msec. each. Frequencies from 8 kc upward were used. CM, AP and SP were all identified up to 48 kc. Here the thresholds for all three responses were nearly identical, but at 12 kc the threshold for SP was higher and for AP much lower than for CM. SP was prominent at high frequencies, and at high intensities its voltage often exceeded that of either AP or CM. The latency from CM to the foot of AP diminishes with increase of intensity and also with increase of frequency. At threshold at 8 kc it was 2.3 msec. and at 30 kc it was 1.4 msec. At all frequencies it approached 1.0 msec. asymptotically as the intensity was increased. The minimal duration needed for maximum AP (measured for a given ratio of stimulus intensity to the usual threshold intensity) was shorter with greater intensity ratios but was independent of frequency.