ON THE EFFECT OF INTERAURAL PHASE DIFFERENCES ON LOUDNESS

The loudness of four monaurally presented Gaussian shaped, 60-ms tone bursts was matched to that of four similar pulses presented binaurally. The stimuli to be matched were all presented in continuous binaural noise of three levels and, in different experiments, either the monaural or the binaural stimuli were adjusted by the observer. With 250- and 710-Hz tone bursts, there are large differences in loudness that, at low signal-to-noise ratios, depend on the interaural phase conditions in a manner consistent with the changes in masked threshold produced by the phase manipulation; there is little, if any, effect of interaural phase on loudness for 2-kHz signals. The effect of interaural phase on loudness decreases with increasing level but, at 250 Hz, remains measurable some 30-40 dB above masked threshold. The matching function for signals out-of-phase grows in proportion to the level to be matched over the entire range from masked threshold to the highest level used. In contrast, for the in-phase condition, the observers show a step at a level that depends both on frequency and on the observer from proportional growth near thresholds to parallel proportional growth some 6 to 12 dB higher.