{"id":{"repo_id":"aachen","oai_identifier":"oai:publications.rwth-aachen.de:63198"},"canonical_url":"https://search.dev.ndltd.org/etd/aachen/oai:publications.rwth-aachen.de:63198","repository":{"repo_id":"aachen","name":"RWTH Aachen University","base_url":"https://publications.rwth-aachen.de/oai2d"},"display":{"title":"Behavioral responses to frequency specific head related transfer functions as filtered by the facial ruff in the Barn owl (Tyto alba)","abstract":"The barn owl is, due to its numerous morphological and neuronal adaptations to sound localization, a long-established model animal for the auditory system. Besides extensive research on the topic within the last decades, it is still unclear how direction- and frequency-dependent physical cues (interaural time differences (ITDs), level differences (ILDs) and monaural spectra) contribute to sound localization especially in the elevational plane. A further open question is to what extent frequency integration is needed for accurate localization, and how the owl can resolve spatial coding ambiguities. Although the diotic stimulation via headphones allows to introduce and manipulate ITDs and ILDs independently, it does not reflect the monaural frequency characteristics that are usually present in free-field stimuli. This problem can be overcome when sound stimuli are filtered by the animal's characteristic head-related transfer functions (HRTFs), creating a Virtual Auditory Space. In the present thesis, I investigated the properties of HRTFs in the American Barn owl (Tyto alba pratincola, L.). The shape of the owls' HRTFs is crucially influenced by the filtering properties of the facial ruff. Therefore, I analyzed the physical cues used for sound localization which are contained in the HRTFs after filtering by the outer ear and ruff. Furthermore, I tested the impact of HRTFs measured under different conditions and in various frequency bands on the owls' sound localization ability in a behavioral task. During the experiments, two methodological approaches were used. First, HRTFs were measured and analyzed under various conditions. The binaural and monaural cues to sound location were assessed in a large set of barn owl HRTFs, including existing HRTFs measured in earlier experiments. Either anesthetized or dead animals were used for a detailed analysis of whether the physiological condition or the body temperature have any influence on the sound localization cues. The analysis focused especially on the low-frequency range (<2 kHz), the role of which is still obscure in the owl. At low frequencies, the owl's ears might act as pressure difference receivers, with both ear cavities being coupled through the interaural canal. In that case, the low-frequency ITD range would be predicted to increase compared to the high-frequency range. However, I did not find such an effect, which argues against the hypothesis of a pressure difference receiver characteristic of the owl's ears. Second, HRTF-filtered stimuli were calculated for stimulation of barn owls in a Virtual Acoustic Space. The sound localization ability of three owls was tested in a behavioral paradigm utilizing saccadic head-turn responses as a measure for the perceived sound source location. In a first approach, the influence of the facial ruff was investigated by virtual removal of the ruff. This was done by comparing azimuthal and elevational head-turn reactions to normal, individualized HRTFs with reactions to normal, non-individualized respectively to “ruffcut” HRTFs. The HRTFs used for that part of the thesis had been recorded near the eardrum of the respective owl during stimulation with tonal sweeps. Measurements had been repeated after successively removing the ruff feathers of a reference owl (owl 39), which resulted in a set of HRTFs for representative spatial sound source locations and with different ruff conditions, depending on which part of the ruff feathers were removed. As expected from the directionality of the ruff, I found that the owls were impaired in their localization ability when the ruff feathers were virtually removed. This impairment included an inability to distinguish stimuli containing the same ITD, but coming from either the front or the rear hemisphere, respectively. The owls distinguished such stimuli only when the HRTFs had been measured with intact ruff, but not after virtual ruff removal. Furthermore, elevational sound localization was severely reduced in the latter stimulus condition. In a second experimental series, the influence of 1/3 octaveband-filtered HRTFs with center frequencies ranging from 1 to 9 kHz was tested in the same behavioral paradigm. The owls localized the stimuli with good azimuthal accuracy, but located stimulus elevation accurately only for frequencies above 3 kHz. Localization errors depended on center frequency. When the ILD of 1/3 octaveband-filtered stimuli with 5 kHz center frequency was fixed to 0 dB, the owls seemed to experience phantom sound sources and were unable to discriminate stimulus elevation, as they did with unmanipulated stimuli. The results presented in the thesis demonstrate that the facial ruff of barn owls alters incoming sound in a frequency-specific way that is not only crucial for accurate sound localization in both azimuthal and elevational planes, but can also be predicted from the filtering properties of the ruff.","abstract_html":"The barn owl is, due to its numerous morphological and neuronal adaptations to sound localization, a long-established model animal for the auditory system. Besides extensive research on the topic within the last decades, it is still unclear how direction- and frequency-dependent physical cues (interaural time differences (ITDs), level differences (ILDs) and monaural spectra) contribute to sound localization especially in the elevational plane. A further open question is to what extent frequency integration is needed for accurate localization, and how the owl can resolve spatial coding ambiguities. Although the diotic stimulation via headphones allows to introduce and manipulate ITDs and ILDs independently, it does not reflect the monaural frequency characteristics that are usually present in free-field stimuli. This problem can be overcome when sound stimuli are filtered by the animal&#x27;s characteristic head-related transfer functions (HRTFs), creating a Virtual Auditory Space. In the present thesis, I investigated the properties of HRTFs in the American Barn owl (Tyto alba pratincola, L.). The shape of the owls&#x27; HRTFs is crucially influenced by the filtering properties of the facial ruff. Therefore, I analyzed the physical cues used for sound localization which are contained in the HRTFs after filtering by the outer ear and ruff. Furthermore, I tested the impact of HRTFs measured under different conditions and in various frequency bands on the owls&#x27; sound localization ability in a behavioral task. During the experiments, two methodological approaches were used. First, HRTFs were measured and analyzed under various conditions. The binaural and monaural cues to sound location were assessed in a large set of barn owl HRTFs, including existing HRTFs measured in earlier experiments. Either anesthetized or dead animals were used for a detailed analysis of whether the physiological condition or the body temperature have any influence on the sound localization cues. The analysis focused especially on the low-frequency range (&lt;2 kHz), the role of which is still obscure in the owl. At low frequencies, the owl&#x27;s ears might act as pressure difference receivers, with both ear cavities being coupled through the interaural canal. In that case, the low-frequency ITD range would be predicted to increase compared to the high-frequency range. However, I did not find such an effect, which argues against the hypothesis of a pressure difference receiver characteristic of the owl&#x27;s ears. Second, HRTF-filtered stimuli were calculated for stimulation of barn owls in a Virtual Acoustic Space. The sound localization ability of three owls was tested in a behavioral paradigm utilizing saccadic head-turn responses as a measure for the perceived sound source location. In a first approach, the influence of the facial ruff was investigated by virtual removal of the ruff. This was done by comparing azimuthal and elevational head-turn reactions to normal, individualized HRTFs with reactions to normal, non-individualized respectively to “ruffcut” HRTFs. The HRTFs used for that part of the thesis had been recorded near the eardrum of the respective owl during stimulation with tonal sweeps. Measurements had been repeated after successively removing the ruff feathers of a reference owl (owl 39), which resulted in a set of HRTFs for representative spatial sound source locations and with different ruff conditions, depending on which part of the ruff feathers were removed. As expected from the directionality of the ruff, I found that the owls were impaired in their localization ability when the ruff feathers were virtually removed. This impairment included an inability to distinguish stimuli containing the same ITD, but coming from either the front or the rear hemisphere, respectively. The owls distinguished such stimuli only when the HRTFs had been measured with intact ruff, but not after virtual ruff removal. Furthermore, elevational sound localization was severely reduced in the latter stimulus condition. In a second experimental series, the influence of 1/3 octaveband-filtered HRTFs with center frequencies ranging from 1 to 9 kHz was tested in the same behavioral paradigm. The owls localized the stimuli with good azimuthal accuracy, but located stimulus elevation accurately only for frequencies above 3 kHz. Localization errors depended on center frequency. When the ILD of 1/3 octaveband-filtered stimuli with 5 kHz center frequency was fixed to 0 dB, the owls seemed to experience phantom sound sources and were unable to discriminate stimulus elevation, as they did with unmanipulated stimuli. The results presented in the thesis demonstrate that the facial ruff of barn owls alters incoming sound in a frequency-specific way that is not only crucial for accurate sound localization in both azimuthal and elevational planes, but can also be predicted from the filtering properties of the ruff.","abstract_has_math":false,"creators":["Hausmann, Elena Laura"],"institution":"Publikationsserver der RWTH Aachen University","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Wagner, Hermann"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2010,"date_issued":"2010","date_published":"2010","updated_at":"2026-07-30T19:43:35Z","subjects":["info:eu-repo/classification/ddc/570","Schleiereule","Psychophysik","Biowissenschaften, Biologie","Kopfübertragungsfunktion","barn owl","behavior","head-related transfer function","psychophysics","auditory"],"languages":["eng"],"rights":["info:eu-repo/semantics/openAccess"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124645%22"],"render_values":[{"text":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124645%22","href":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124645%22","code":true}]}]},"links":{"outbound_url":"https://publications.rwth-aachen.de/record/63198","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Wagner, Hermann"]},{"key":"dc:creator","label":"Author","values":["Hausmann, Elena Laura"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:coverage","label":"Dc Coverage","values":["DE"]},{"key":"dc:date","label":"Dc Date","values":["2010"]},{"key":"dc:publisher","label":"Institution","values":["Publikationsserver der RWTH Aachen University"]},{"key":"dc:relation","label":"Dc Relation","values":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-33798"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["info:eu-repo/classification/ddc/570","Schleiereule","Psychophysik","Biowissenschaften, Biologie","Kopfübertragungsfunktion","barn owl","behavior","head-related transfer function","psychophysics","auditory"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/record/63198","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124645%22"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The barn owl is, due to its numerous morphological and neuronal adaptations to sound localization, a long-established model animal for the auditory system. Besides extensive research on the topic within the last decades, it is still unclear how direction- and frequency-dependent physical cues (interaural time differences (ITDs), level differences (ILDs) and monaural spectra) contribute to sound localization especially in the elevational plane. A further open question is to what extent frequency integration is needed for accurate localization, and how the owl can resolve spatial coding ambiguities. Although the diotic stimulation via headphones allows to introduce and manipulate ITDs and ILDs independently, it does not reflect the monaural frequency characteristics that are usually present in free-field stimuli. This problem can be overcome when sound stimuli are filtered by the animal's characteristic head-related transfer functions (HRTFs), creating a Virtual Auditory Space. In the present thesis, I investigated the properties of HRTFs in the American Barn owl (Tyto alba pratincola, L.). The shape of the owls' HRTFs is crucially influenced by the filtering properties of the facial ruff. Therefore, I analyzed the physical cues used for sound localization which are contained in the HRTFs after filtering by the outer ear and ruff. Furthermore, I tested the impact of HRTFs measured under different conditions and in various frequency bands on the owls' sound localization ability in a behavioral task. During the experiments, two methodological approaches were used. First, HRTFs were measured and analyzed under various conditions. The binaural and monaural cues to sound location were assessed in a large set of barn owl HRTFs, including existing HRTFs measured in earlier experiments. Either anesthetized or dead animals were used for a detailed analysis of whether the physiological condition or the body temperature have any influence on the sound localization cues. The analysis focused especially on the low-frequency range (<2 kHz), the role of which is still obscure in the owl. At low frequencies, the owl's ears might act as pressure difference receivers, with both ear cavities being coupled through the interaural canal. In that case, the low-frequency ITD range would be predicted to increase compared to the high-frequency range. However, I did not find such an effect, which argues against the hypothesis of a pressure difference receiver characteristic of the owl's ears. Second, HRTF-filtered stimuli were calculated for stimulation of barn owls in a Virtual Acoustic Space. The sound localization ability of three owls was tested in a behavioral paradigm utilizing saccadic head-turn responses as a measure for the perceived sound source location. In a first approach, the influence of the facial ruff was investigated by virtual removal of the ruff. This was done by comparing azimuthal and elevational head-turn reactions to normal, individualized HRTFs with reactions to normal, non-individualized respectively to “ruffcut” HRTFs. The HRTFs used for that part of the thesis had been recorded near the eardrum of the respective owl during stimulation with tonal sweeps. Measurements had been repeated after successively removing the ruff feathers of a reference owl (owl 39), which resulted in a set of HRTFs for representative spatial sound source locations and with different ruff conditions, depending on which part of the ruff feathers were removed. As expected from the directionality of the ruff, I found that the owls were impaired in their localization ability when the ruff feathers were virtually removed. This impairment included an inability to distinguish stimuli containing the same ITD, but coming from either the front or the rear hemisphere, respectively. The owls distinguished such stimuli only when the HRTFs had been measured with intact ruff, but not after virtual ruff removal. Furthermore, elevational sound localization was severely reduced in the latter stimulus condition. In a second experimental series, the influence of 1/3 octaveband-filtered HRTFs with center frequencies ranging from 1 to 9 kHz was tested in the same behavioral paradigm. The owls localized the stimuli with good azimuthal accuracy, but located stimulus elevation accurately only for frequencies above 3 kHz. Localization errors depended on center frequency. When the ILD of 1/3 octaveband-filtered stimuli with 5 kHz center frequency was fixed to 0 dB, the owls seemed to experience phantom sound sources and were unable to discriminate stimulus elevation, as they did with unmanipulated stimuli. The results presented in the thesis demonstrate that the facial ruff of barn owls alters incoming sound in a frequency-specific way that is not only crucial for accurate sound localization in both azimuthal and elevational planes, but can also be predicted from the filtering properties of the ruff."]},{"key":"dc:source","label":"Dc Source","values":["Aachen : Publikationsserver der RWTH Aachen University IV, 120 S. : Ill., graph. Darst. (2010). = Aachen, Techn. Hochsch., Diss., 2010"]},{"key":"dc:title","label":"Title","values":["Behavioral responses to frequency specific head related transfer functions as filtered by the facial ruff in the Barn owl (Tyto alba)"]}]}],"canonical_facts":{"dc:contributor":["Wagner, Hermann"],"dc:coverage":["DE"],"dc:creator":["Hausmann, Elena Laura"],"dc:date":["2010"],"dc:description":["The barn owl is, due to its numerous morphological and neuronal adaptations to sound localization, a long-established model animal for the auditory system. Besides extensive research on the topic within the last decades, it is still unclear how direction- and frequency-dependent physical cues (interaural time differences (ITDs), level differences (ILDs) and monaural spectra) contribute to sound localization especially in the elevational plane. A further open question is to what extent frequency integration is needed for accurate localization, and how the owl can resolve spatial coding ambiguities. Although the diotic stimulation via headphones allows to introduce and manipulate ITDs and ILDs independently, it does not reflect the monaural frequency characteristics that are usually present in free-field stimuli. This problem can be overcome when sound stimuli are filtered by the animal's characteristic head-related transfer functions (HRTFs), creating a Virtual Auditory Space. In the present thesis, I investigated the properties of HRTFs in the American Barn owl (Tyto alba pratincola, L.). The shape of the owls' HRTFs is crucially influenced by the filtering properties of the facial ruff. Therefore, I analyzed the physical cues used for sound localization which are contained in the HRTFs after filtering by the outer ear and ruff. Furthermore, I tested the impact of HRTFs measured under different conditions and in various frequency bands on the owls' sound localization ability in a behavioral task. During the experiments, two methodological approaches were used. First, HRTFs were measured and analyzed under various conditions. The binaural and monaural cues to sound location were assessed in a large set of barn owl HRTFs, including existing HRTFs measured in earlier experiments. Either anesthetized or dead animals were used for a detailed analysis of whether the physiological condition or the body temperature have any influence on the sound localization cues. The analysis focused especially on the low-frequency range (<2 kHz), the role of which is still obscure in the owl. At low frequencies, the owl's ears might act as pressure difference receivers, with both ear cavities being coupled through the interaural canal. In that case, the low-frequency ITD range would be predicted to increase compared to the high-frequency range. However, I did not find such an effect, which argues against the hypothesis of a pressure difference receiver characteristic of the owl's ears. Second, HRTF-filtered stimuli were calculated for stimulation of barn owls in a Virtual Acoustic Space. The sound localization ability of three owls was tested in a behavioral paradigm utilizing saccadic head-turn responses as a measure for the perceived sound source location. In a first approach, the influence of the facial ruff was investigated by virtual removal of the ruff. This was done by comparing azimuthal and elevational head-turn reactions to normal, individualized HRTFs with reactions to normal, non-individualized respectively to “ruffcut” HRTFs. The HRTFs used for that part of the thesis had been recorded near the eardrum of the respective owl during stimulation with tonal sweeps. Measurements had been repeated after successively removing the ruff feathers of a reference owl (owl 39), which resulted in a set of HRTFs for representative spatial sound source locations and with different ruff conditions, depending on which part of the ruff feathers were removed. As expected from the directionality of the ruff, I found that the owls were impaired in their localization ability when the ruff feathers were virtually removed. This impairment included an inability to distinguish stimuli containing the same ITD, but coming from either the front or the rear hemisphere, respectively. The owls distinguished such stimuli only when the HRTFs had been measured with intact ruff, but not after virtual ruff removal. Furthermore, elevational sound localization was severely reduced in the latter stimulus condition. In a second experimental series, the influence of 1/3 octaveband-filtered HRTFs with center frequencies ranging from 1 to 9 kHz was tested in the same behavioral paradigm. The owls localized the stimuli with good azimuthal accuracy, but located stimulus elevation accurately only for frequencies above 3 kHz. Localization errors depended on center frequency. When the ILD of 1/3 octaveband-filtered stimuli with 5 kHz center frequency was fixed to 0 dB, the owls seemed to experience phantom sound sources and were unable to discriminate stimulus elevation, as they did with unmanipulated stimuli. The results presented in the thesis demonstrate that the facial ruff of barn owls alters incoming sound in a frequency-specific way that is not only crucial for accurate sound localization in both azimuthal and elevational planes, but can also be predicted from the filtering properties of the ruff."],"dc:identifier":["https://publications.rwth-aachen.de/record/63198","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124645%22"],"dc:language":["eng"],"dc:publisher":["Publikationsserver der RWTH Aachen University"],"dc:relation":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-33798"],"dc:rights":["info:eu-repo/semantics/openAccess"],"dc:source":["Aachen : Publikationsserver der RWTH Aachen University IV, 120 S. : Ill., graph. Darst. (2010). = Aachen, Techn. Hochsch., Diss., 2010"],"dc:subject":["info:eu-repo/classification/ddc/570","Schleiereule","Psychophysik","Biowissenschaften, Biologie","Kopfübertragungsfunktion","barn owl","behavior","head-related transfer function","psychophysics","auditory"],"dc:title":["Behavioral responses to frequency specific head related transfer functions as filtered by the facial ruff in the Barn owl (Tyto alba)"],"dc:type":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]},"updated_at":"2026-07-30T19:43:35Z"}