Acoustic trauma effects from doubling the exposure time.

Guinea pigs were used to test acoustic trauma effects from doubling the exposure time. Previously, two frequencies (20 kHz and 4 kHz) were used in conjunction with each other (ie double exposure) to see whether a prior exposure of the cochlea to one frequency would alter the extent of damage caused by a secondary frequency, when compared with damage caused by either frequency alone. A reduced area of damage was attained after double exposures. To complete the series, the same two frequencies were used separately, but the exposure time was doubled. The results from the 20 kHz series surprisingly indicated that a reduced area of damage was obtained after doubling the exposure time. No significant differences were found in the 4 kHz series.