P3.147 Friday, Jan. 6 The interaural canal of the barn owl, Tyto alba GANS , Elizabeth*; WILLIS, Katie L; BIERMAN, Hillary; CARR, Catherine; Univ. of Maryland, College Park email@example.com
The interaural canal of birds allows for phase interaction on both sides of the tympanum, thus increasing the effective separation of the ears to produce larger interaural delays than would be predicted from the head width (Calford and Piddington, 1988). The canal, however, appears ineffective at frequencies above about 4 kHz. At lower frequencies, however, ipsilateral and contralateral inputs interact at the tympanum (Moiseff and Konishi, 1981). We have therefore measured the extent of the middle ear cavity and associated sinuses in the barn owl, Tyto alba. We used microMRI (7T) scans of the barn owl head with a resolution of 195μm3 per voxel. Image stacks were constructed in 3-D using Neurolucida (Microbrightfield) by tracing the cavities and measuring their volumes. The interaural canals on each side had a diameter of about 1.8 mm as they exited the middle ear cavity, and formed large ventrally directed tubes which were united in the expansive rostral tympanic recess. This recess was about 1.5 cm in rostrocaudal extent. Our measurements were consistent with those from the great horned owl (Witmer et al, 2008), and also consistent with recordings of large interaural delays at low best frequencies in the barn owl (Koppl and Carr, 2004).