Interaural correlation and the binaural summation of loudness

The effect of interaural correlation (rho) on the loudness for noisebands was measured using a loudness-matching task in naive listeners. The task involved a sequence of loudness comparisons for which the intensity of one stimulus in a given comparison was varied using a one-up-one-down adaptive rule. The task provided an estimate of the level difference (in decibels) for which two stimulus conditions have equal loudness, giving measures of loudness difference in equivalent decibel units (dB(equiv)). Concurrent adaptive tracks measured loudness differences between rho=1, 0, and -1 and between these binaural stimuli and the monaural case for various noisebands. For all noisebands, monaural stimuli required approximately 6 dB higher levels than rho=1 for equal loudness. For most noisebands, rho=1 and rho=-1 were almost equal in loudness, with rho=-1 being slightly louder in the majority of measurements, while rho=0 was about 2 dB(equiv) louder than rho=1 or rho=-1. However, noisebands with significant high-frequency energy showed smaller differences: for 3745-4245 Hz, rho=0 was only about 0.85 dB(equiv) louder than rho=+/-1, and for 100-5000 Hz it was non-significantly louder (perhaps 0.7 dB(equiv)).