Binaural Thresholds of Pulsive Signals and Place of Detection on the Basilar Membrane

Abstract

Absolute and masked binaural thresholds are measured for an ensemble of pulsive periodic signals. Spectral composition, interaural time, and pulse rate are signal parameters. Broad-band, interaurally in-phase noise is the masker. From threshold behavior and from masking-level differences (MLD's), evidence is deduced concerning place of detection on the basilar membrane. The experimental observations are supported by calculations of root-mean-square signal-to-noise displacement along the membrane, using Flanagan's model for membrane motion. A typical result of the study shows that a periodic train of unipolar impulses, produced at a rate of 250 pps, has (1) an absolute threshold determined by motion near the 1000- to 2000-cps region of the membrane; (2) an homophasic masked threshold determined by motion near the 250- to 600-cps region of the membrane; and (3) an MLD (or homoheterophasic threshold difference) determined by the spectral presence of the fundamental component. In particular, the findings provide further information about the peripheral processing involved in binaural detection of complex signals.