Auditory brainstem response recovery rates during double-pulse presentation in the false killer whale (Pseudorca crassidens): A mechanism of automatic gain control?

Abstract

The outgoing echolocation pulse and the return echo response can be approximately examined in the auditory system of an echolocating animal by presenting two pulses and determining the forward-masking effect of the first pulse on the response to the second pulse using auditory-evoked potential procedures. False killer whale, Pseudorca crassidens, auditory brainstem responses (ABR) were recorded using a double-click stimulation paradigm specifically measuring the recovery of the second (test) response (to the second click) as a function of the length of the interclick interval (ICI) following various levels of the first (conditioning) click. At all click intensities, the slopes of the recovery functions were almost constant: 0.60.8 V per ICI decade. Therefore, even when the conditioning-to-click level ratio was kept constant, the duration of recovery was intensity dependent: the higher intensity the longer the recovery. The conditioning-to-test-click level ratio strongly influenced the recovery time: the higher the ratio, the longer the recovery. This dependence was nearly linear, using a logarithmic ICI scale with a rate of 2530 dB per ICI decade. These data were used for modeling the interaction between the emitted click and the echo in the auditory system during echolocation.