AP threshold elevation in the guinea pig following exposure to a broadband noise

Sixty guinea pigs were exposed to a steady‐state broadband noise with a falling frequency spectrum. The sound‐pressure level was varied between 96 and 117 dB SPL, and the duration of the exposure was varied from 3 to 12 h. After 4–5 weeks, the auditory thresholds were determined by electrocochleography at 14 frequencies, and the results were compared with a control group. With increasing sound‐pressure level, the thresholds became elevated at all frequencies. The maximum threshold elevation also exhibited a slight shift toward higher frequencies. With increasing exposure time, the threshold elevations increased and shifted into the high‐frequency region, whereas the low‐frequency region was less affected. Linear regression analysis showed that the average threshold elevation between 1 and 20 kHz did not deviate from that predicted by the equal‐energy hypothesis. However, the high‐frequency loss at 5–20 kHz was very dependent on the exposure time, whereas the 1‐ to 4‐kHz loss was not. There was no sign of any critical intensity with sudden increments in threshold elevation.