Sound localization and delay lines--do mammals fit the model?

The current dominant model of binaural sound localization proposes that the lateral position of a sound source is determined by the position of maximal activation within an array of binaural coincidence-detector neurons that are tuned to different interaural time differences (ITDs). The tuning of a neuron for an ITD is determined by the difference in axonal conduction delay from each ear--the so-called "delay line" hypothesis. Although studies in birds appear to support this model, recent evidence from mammals suggests that the model does not provide accurate descriptions of how ITDs are encoded in the mammalian auditory brainstem or of how ITD-sensitive neurons contribute to mammalian sound localization.