Stochastic properties of auditory brainstem coincidence detectors in binaural perception

In the mammalian auditory brainstem, two types of coincidence detector cells are involved in binaural localization: excitatory-excitatory (EE) and excitatory-inhibitory (EI). Using statistics derived from EE and EI spike trains, binaural discrimination abilities of single tones were predicted. The minimum audible angle (MAA), as well as the just noticeable difference of interaural time delay (ITD) and interaural level difference (ILD) were analytically derived for both EE and EI cells on the basis of two possible neural coding patterns, rate coding that ignores a spike's timing information and all-information coding (AIN), which considers a spike's timing occurrences. Simulation results for levels below saturation were qualitatively compared to experimental data, which yielded the following conclusions: (1) ITD is primarily estimated by EE cells with AIN coding when the ipsilateral auditory input exhibits phase delay between 40 degrees and 65 degrees. (2) In ILD, both AIN and rate coding provide identical performances. It is most likely that ILD is primarily estimated by EI cells according to rate coding, and for ILD the information derived from the spikes' timing is redundant. (3) For MAA estimation, the derivation should take into account ambiguous directions of a source signal in addition to its true value.