Effect of Interaural Phase on the Binaural Absolute Threshold for Tone

Abstract

Earlier workers have found that where monaural thresholds are equal, or where inequalities are compensated for, the binaural threshold is about 3 db lower than the monaural. Licklider in Steven's Handbook suggests that this implies a kind of power summation. Since the powers being summated are going to different ears, this summation cannot be acoustical. The summation, therefore, appears to be neural, and we should expect some of the temporal phenomena of neural summation to apply. Delaying the sound to one ear, for instance, should make conditions less favorable for summation and should raise the binaural threshold. In the present experiment a 2-msec delay (or advance) was produced by reversing the phase of a 250-cps tone. Monaural and binaural thresholds (both homophasic and antiphasic) were determined for four subjects, and the best ear was taken as reference. The results indicate that the threshold for the antiphasic condition instead of being elevated relative to the homophasic is actually lower. This suggests that we are dealing, not with neural summation, but with a masking phenomenon—that the absolute threshold is really a masked threshold. [This Work was partially supported by the Bureau of Ships.]