Fig. 2. (A) Auditory evoked potentials (AEPs) from a bamboo shark in response to a 100 Hz signal at four signal levels. As the signal is decreased in level (particle acceleration, m s^-2) the AEP signal also decreases until it is lost in the noise at 1.0^-4 m s^-2. (B) 2048 fast fourier transform (FFT) of the same AEP for the bamboo shark in response to a 100 Hz sound. The arrow indicates the frequency doubling peak, which occurs at 200 Hz. A positive detection is when the peak (at twice the frequency played) is at least 3 dB above the noise floor. The noise floor is estimated from the AEP power spectrum with a window of 100 Hz around the doubling frequency. (C) Pressure and particle velocity raw signals as recorded from the pressure/velocity probe. This example of particle velocity has been recorded in the z-axis. P, pressure; V, velocity.