Responses to dichotic tone-in-noise stimuli in the inferior colliculus

Human listeners are more sensitive to tones embedded in diotic noise when the tones are out-of-phase at the two ears (N₀S_π) than when they are in-phase (N₀S₀). The difference between the tone-detection thresholds for these two conditions is referred to as the binaural masking level difference (BMLD) and reflects a benefit of binaural processing. Detection in the N₀S_π condition has been explained in modeling studies by changes in interaural correlation (IAC), but this model has only been directly tested physiologically for low frequencies. Here, the IAC-based hypothesis for binaural detection was examined across a wide range of frequencies and masker levels using recordings in the awake rabbit inferior colliculus (IC). IAC-based cues were strongly correlated with neural responses to N₀S_π stimuli. Additionally, average rate-based thresholds were calculated for both N₀S₀ and N₀S_π conditions. The rate-based neural BMLD at 500 Hz matched rabbit behavioral data, but the trend of neural BMLDs across frequency differed from that of humans.