PARADOXICAL LATERAL SUPPRESSION IN THE DOLPHINS AUDITORY-SYSTEM - WEAK SOUNDS SUPPRESS RESPONSE TO STRONG SOUNDS

A paradoxical phenomenon was found in the auditory system of dolphins: weak sounds suppressed the brain responses to much stronger sounds. T his occurred when the brain evoked potentials to rhythmic sound amplit ude modulations were recorded. The response was markedly suppressed by addition of another sound of higher frequency and down to 40 dB lower intensity than the amplitude-modulated signal. Only the sustained rhy thmic response was suppressed while transient on-response was not, thu s indicating that the suppression influenced the ability of evoked pot entials to follow rapid amplitude modulations. This prevents weak soun ds from being masked by stronger ones. It may help a dolphin to percei ve weaker echo-signals in the background of stronger emitted pulses. ( C) 1997 Elsevier Science Ireland Ltd.