Interaural correlation and the binaural summation of loudness^a)

The effect of interaural correlation $(ρ)$ on the loudness for noisebands was measured using a loudness-matching task in naïve 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 $(dBequiv)$⁠. Concurrent adaptive tracks measured loudness differences between $ρ=1$⁠, 0, and $−1$ and between these binaural stimuli and the monaural case for various noisebands. For all noisebands, monaural stimuli required approximately $6dB$ higher levels than $ρ=1$ for equal loudness. For most noisebands, $ρ=1$ and $ρ=−1$ were almost equal in loudness, with $ρ=−1$ being slightly louder in the majority of measurements, while $ρ=0$ was about $2dBequiv$ louder than $ρ=1$ or $ρ=−1$⁠. However, noisebands with significant high-frequency energy showed smaller differences: for $3745–4245Hz$⁠, $ρ=0$ was only about $0.85dBequiv$ louder than $ρ=±1$⁠, and for $100–5000Hz$ it was non-significantly louder (perhaps $0.7dBequiv$⁠).