In behavioral and chronic electrophysiological studies on monkeys exposed to octave band noise, cochlear microphonic and action-potential responses to puretone bursts were compared to behaviorally obtained thresholds from the same animals. The following results were obtained: (1) Behavioral pure-tone thresholds were within 3 dB of cochlear action-potential thresholds before noise exposure. However, during recovery from noise exposure, action-potential thresholds were as much as 10 dB lower, suggesting the possibility of physiological "masking." (2) Input-output functions for the cochlear action potentials during these recovery periods strongly resembled loudness recruitment functions, and maximum voltages obtained frequently exceeded preexposure values. Several reasonable explanations for post-exposure loudness recruitment exist, but the basis of the marked transient increase in cochlear electrical activity is still open to speculation. A circulatory rebound phenomenon may be involved.
James E. Pugh, Milton R. Horwitz, David J. Anderson. Cochlear Electrical Activity in Noise-Induced Hearing LossBehavioral and Electrophysiological Studies in Primates. Arch Otolaryngol. 1974;100(1):36–40. doi:10.1001/archotol.1974.00780040040008