Response adaptation in the barn owl's auditory space map.

Response adaptation is the change of the firing rate of neurons induced by a preceding stimulus. It can be found in many sensory systems and throughout the auditory pathway. We investigated response adaptation in the external nucleus of the inferior colliculus (ICX) of barn owls ( Tyto furcata), a nocturnal bird of prey and specialist in sound localization.

The representation of sound localization cues in the barn owl's inferior colliculus.

The barn owl is a well-known model system for studying auditory processing and sound localization. This article reviews the morphological and functional organization, as well as the role of the underlying microcircuits, of the barn owl's inferior colliculus (IC). We focus on the processing of frequency and interaural time (ITD) and level differences (ILD).

Adaptation in the auditory midbrain of the barn owl (Tyto alba) induced by tonal double stimulation.

During hunting, the barn owl typically listens to several successive sounds as generated, for example, by rustling mice. As auditory cells exhibit adaptive coding, the earlier stimuli may influence the detection of the later stimuli. This situation was mimicked with two double-stimulus paradigms, and adaptation was investigated in neurons of the barn owl's central nucleus of the inferior colliculus.

Estimated cochlear delays in low best-frequency neurons in the barn owl cannot explain coding of interaural time difference.

The functional role of the low-frequency range (<3 kHz) in barn owl hearing is not well understood. Here, it was tested whether cochlear delays could explain the representation of interaural time difference (ITD) in this frequency range. Recordings were obtained from neurons in the core of the central nucleus of the inferior colliculus.

Target-approaching behavior of barn owls (Tyto alba): influence of sound frequency.

We studied the influence of frequency on sound localization in free-flying barn owls by quantifying aspects of their target-approaching behavior to a distant sound source during ongoing auditory stimulation. In the baseline condition with a stimulus covering most of the owls hearing range (1-10 kHz), all owls landed within a radius of 20 cm from the loudspeaker in more than 80% of the cases and localization along the azimuth was more accurate than localization in elevation. When the stimulus contained only high frequencies (>5 kHz) no changes in striking behavior were observed.

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.

In-flight corrections in free-flying barn owls (Tyto alba) during sound localization tasks.

Barn owls localize a stationary auditory target with high accuracy. They might also be able to hit a target that is intermittently moving while the owl is approaching. If so, there should be a critical delay before strike initiation, up to which the owl can adapt its flight path to a new stimulus position.