Abstract:

Barn owls use interaural time difference (ITD) to localize sound sources in azimuth. For a long time, the Jeffress model was recognized as an excellent description of the representation of ITD in vertebrates. This view has recently been challenged by data from the mammalian auditory system. Here I demonstrate that, in the barn owl's brain, correlates for all feature of the Jeffress model are found. Specifically, there are delay lines, coincidence detectors, computations in narrow frequency bands, representations of ITD beyond the 90-degrees limit, and a distribution of ITD over the whole phase space for both low- and high-frequency neurons. The temporal precision as measured by the relative time measure of phase delay is sharper than 20 microseconds. Across-frequency integration leads to an unambiguous representation in the external nucleus of the inferior colliculus. New studies on the representation of binaural masking level differences show that the wideband neurons in external nucleus of the inferior colliculus are suited for localization, while the responses in narrowband neurons of the inputs to the external nucleus of the inferior colliculus are more suited for detection.