6.2 The bilateral comparison: the superior olivary complex

The superior olivary complex (SOC) sits on each side of the medulla and is the first place in the auditory pathway where information from both ears meets in a single neuron. The SOC has two main subdivisions relevant for localization: the medial superior olive (MSO) and the lateral superior olive (LSO). The two divisions perform two different computations on two different cues.

The MSO computes interaural time differences (ITDs) — the microsecond-scale phase information that dominates low-frequency localization. The LSO computes interaural level differences (ILDs) — the decibel-scale intensity comparisons that dominate high-frequency localization. These are the two sides of Rayleigh’s duplex theory from movement 3, made flesh.