In this thesis, properties of the acoustic system and sound-localization behavior of barn owls were investigated. The influence of adaptation on sound localization behavior was examined in the first experiment. Payne (1971) was able to observe that barn owls wait for at least a second sound before they approach their prey. This situation was mimicked in a behavioral experiment to investigate how a preceding stimulus accuracy of the response to the second stimulus. It is known that the response of neurons to a second stimulus is decreased compared to the response to the first stimulus. This phenomenon is called response adaptation. This means that the detection threshold of the second stimulus may be elevated stimulus and, therefore, response-adaptation influences localization accuracy of the owl. Response adaptation was examined with a double stimulus paradigm. The owl had to locate a broadband noise token, which was preceded by another broadband noise token. I found out that the accuracy and precision with which the barn owls localized the sound source, decreased with double stimulation compared to the condition with only a single stimulus. By varying the interval between the end of the first and onset of the second stimulus I was able to show that the adaptive or masking effect of the first stimulus expires after a few hundred milliseconds. The results suggest that waiting for the second stimulus actually caused costs in terms of decreasing accuracy. In the second study, the head-turning behavior was used to compare responses to frequency-modulated and stimuli with stationary stimulus content. Barn owls detect time differences in the arrival of sound at both ears and can thus determine the azimuth of a sound source. When stimulated with narrow-band stationary stimuli, however, barn owls locate so-called phantom sources, i.e. they turn their head to a position that does not correspond to the actual sound source. The position of the phantom source can be predicted by the period of the center frequency and a known factor that converts the time differences in an angle. The percentage of phantom localization was determined as a function of stimulus bandwidth. Phantom sound sources are not localized at high stimulus bandwidths. Integration of frequency information in the auditory pathway of the barn owl leads to a reduction of phantom-source locations. Frequency-modulated tones offered the opportunity to present the same frequency content as with stationary noise, but within a certain time interval. This allows determination of the duration of the time window in which the frequency information is integrated. The behavioral data could be well explained with a model that simulates two important processes in the auditory pathway of the barn owl: 1) binaural interaction 2) integration of frequency information. The time constants of the time windows had a duration between 2 and 17 ms for both model steps and did not depend on the stimulus duration. In the third series of experiments I investigated whether the tympanic membrane of the barn owl functions as pressure receiver or as pressure-gradient receiver. In a pressure receiver, as it occurs in mammals, both middle ears are not acoustically coupled. This means that no sound is transmitted through an intracranial, interaural canal. Especially in small lizards, but also birds, however, there are cavities that couple both middle ears. Sound does not only reach the eardrum from outside, but also through the interaural canal. The incoming signals are phase shifted. The phase shift depends on stimulus location. In the case of lossless sound transmission through the interaural canal certain sound directions lead to complete extinction of the eardrum vibration. Consequently, the reduction of the eardrum vibration also depends on the degree of sound attenuation through the canal. To measure ear coupling the eardrum vibration was measured with a laser Doppler vibrometer. Eardrum vibration was measured as a function of stimulus frequency and azimuth. In addition, the actual attenuation of acoustic signals by the interaural canal was measured. The tympanic membrane was directional up to 3 kHz. That is, the eardrum vibration amplitude varied by more than 3 dB in 360° of stimulation angles. These data can be explained by attenuation of sound through the interaural canal. For frequencies higher than 3 kHz attenuation was too high to produce significant directionality.
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