Forward masking in gerbils: The effect of age

We investigated forward masking in 21 gerbils as a function of age (5–47 months) using 400 ms maskers at 40 dB SPL and a 20 ms, 2.85 kHz probe presented 2.5 ms after the masker. Elevated thresholds for the unmasked probe were only observed in animals older than 3 years. Unmasked thresholds showed no significant age-dependent hearing loss in animals below 3 years of age. In these animals without peripheral hearing loss, we found a significant age-dependent increase of masker-induced threshold shift. A regression analysis revealed that threshold shift increased from 23 dB in 1 year old gerbils to 37 dB in 3 year old animals. Increased forward masking in these animals with no sign of peripheral hearing loss points to a central processing deficit.