Across-channel interaural-level-difference processing demonstrates frequency dependence.

Accurate localization of complex sounds involves combining interaural information across frequencies to produce a single location percept. Interaural level differences (ILDs) are highly frequency dependent and it is unclear how the auditory system combines differing ILDs across frequency. Therefore, ILD just noticeable differences (JNDs) and intracranial lateralization were measured in young normal-hearing listeners using single- and multi-band stimuli. The bands were 300-ms, 10-Hz narrowband noises; the multi-band condition had three bands; they started and ended synchronously; they were located around three different frequency regions (750, 2000, or 4000 Hz); they had five different frequency separations that ranged from unresolved to resolved; the bands were dichotic with the same non-zero ILD (targets) or were diotic with zero ILD (interferers). Results showed single-band ILD JNDs were marginally frequency dependent. If unresolved diotic interferers were added, ILD JNDs increased greatly because of interaural decorrelation. If well-resolved diotic interferers were added, ILD JNDs were frequency dependent and the worst performance occurred when targets were near 1000 or 4000 Hz. This frequency dependence might be partially explained by ILD vs azimuth non-monotonicities for free-field sound sources in this frequency region. These results suggest that binaural processing models need revision for the processing of complex sounds.