Binaural processing in the synthesis of auditory spatial receptive fields.

The owl's auditory system computes interaural time (ITD) and interaural level (ILD) differences to create a two-dimensional map of auditory space. Space-specific neurons are selective for combinations of ITD and ILD, which define, respectively, the horizontal and vertical dimensions of their receptive fields. ITD curves for postsynaptic potentials indicate that ICx neurons integrate the results of binaural cross correlation in different frequency bands. However, the difference between the main and side peaks is slight. ICx neurons further enhance this difference in the process of converting membrane potentials to impulse rates. Comparison of subthreshold postsynaptic potentials (PSPs) and spike output for the same neurons showed that receptive fields measured in PSPs were much larger than those measured in spikes in both ITD and ILD dimensions. A multiplication of separate postsynaptic potentials tuned to ITD and ILD can account for the combination sensitivity of these neurons to ITD-ILD pairs.