Spontaneous oto‐acoustic emission from a chinchilla ear following exposure to noise

Abstract

A spontaneous oto‐acoustic emission (SOAE) was observed in one chinchilla after two exposures to an octave band of noise (OBN) centered at 0.5 kHz, 95 dB SPL, each for 9 days. This SOAE, not present before the second exposure, was a narrow‐band signal at 2.2 kHz that varied from 10–26 dB SPL across recording sessions. The SOAE has remained stable over the 3‐year period since it was discovered. During the past year, this animal has been trained behaviorally so that detection and discrimination thresholds can be determined in the region near the SOAE. Measures of auditory sensitivity at quarter‐octave intervals between 0.125 and 16.0 kHz revealed a hearing loss (re: normal chinchilla) of 22 dB centered at 2.37 kH2. However, thresholds determined at 10‐Hz intervals between 1600 Hz and 2800 Hz showed that the SOAE was correlated generally with a region of enhanced sensitivity in the microstructure of the audiogram. However, in the immediate vicinity of the SOAE thresholds were elevated by 5–10 dB; addition of a tonal masker (2.2 kH2 at 5–20 dB SPL) had no effect on the shape of the audiogram. [Work supported by Grant OH 02128 from NIOSH.]