A Stimulation-Recording Technique for Evaluating Binaural Sound Processing in Porpoises

A semiautomatic system has been developed to evaluate temporal and binaural aspects of the porpoise sonar receiving system at the level of the midbrain. Surgical and electronic techniques are combined to test this fast acting system and permit replication by digital computer. Pulsed-sound projectors were used to binaurally simulate porpoise sonar clicks underwater, in an azimuth about their heads. Precise control of interaural time differences and repetition rates of the projectors was by an oven-regulated crystal time delay generator. Pulse amplitudes were independently determined by dc sources, whose voltages were delivered through silicon-controlled rectifiers (SCR's).