Representation of sound pressure and particle motion information in the midbrain of the goldfish.

1. Averaged evoked responses from multiple electrodes in the goldfish midbrain (torus semicircularis) area were recorded in response to acoustic stimulation by loudspeaker and to direct vertical vibration of the head. 2. Relative pressure and displacement sensitivity was such that in the far field, the response to sound pressure would dominate the response to particle motion by 40-90 dB. 3. Swimbladder deflation caused a flat (70-1000 Hz) loss in pressure sensitivity ranging from 20 to over 50 dB, and led to an enhanced response to vibration at low frequencies. 4. The goldfish midbrain is not homogeneous with regard to relative pressure and motion sensitivity.