Neural correlates of binaural masking level difference in the inferior colliculus of the barn owl (Tyto alba).

Humans and animals are able to detect signals in noisy environments. Detection improves when the noise and the signal have different interaural phase relationships. The resulting improvement in detection threshold is called the binaural masking level difference.

Improvements of sound localization abilities by the facial ruff of the barn owl (Tyto alba) as demonstrated by virtual ruff removal.

Background: When sound arrives at the eardrum it has already been filtered by the body, head, and outer ear. This process is mathematically described by the head-related transfer functions (HRTFs), which are characteristic for the spatial position of a sound source and for the individual ear. HRTFs in the barn owl (Tyto alba) are also shaped by the facial ruff, a specialization that alters interaural time differences (ITD), interaural intensity differences (ILD), and the frequency spectrum of the incoming sound to improve sound localization.

Distribution of interaural time difference in the barn owl's inferior colliculus in the low- and high-frequency ranges.

Interaural time differences are an important cue for azimuthal sound localization. It is still unclear whether the same neuronal mechanisms underlie the representation in the brain of interaural time difference in different vertebrates and whether these mechanisms are driven by common constraints, such as optimal coding. Current sound localization models may be discriminated by studying the spectral distribution of response peaks in tuning curves that measure the sensitivity to interaural time difference.