Brainstem mechanisms contributing to accurate source localisation are suited to the reverberant structure of natural acoustic scenes

Listeners perceive sound energy as originating from the direction of its source, even when followed only milliseconds later by reflected energy from multiple different directions. Here, modelling responses of brainstem neurons responsible for encoding auditory spatial cues, we demonstrate that accurate localisation in reverberant environments relies on pre- and post-synaptic specializations that emphasise spatial information in early-arriving sound energy. Synaptic depression in spherical bushy cells (SBCs) of the cochlear nucleus, and outwardly-rectifying membrane currents in SBCs and neurons of the medial superior olive (MSO) to which SBCs project bilaterally, are necessary to account for human listening performance. These biophysical properties appear suited to efficient coding of spatial information, emphasising early-arriving spatial information, particularly at sound frequencies where reverberant energy is relatively intense. Applied to lateralisation of human speech in a virtual reverberant room, we show that frequency-dependent membrane properties enhance correct, over spurious, localisation cues at the earliest stages of spatial processing.