Biological Cybernetics

, Volume 110, Issue 4–5, pp 319–331 | Cite as

Role of intracranial cavities in avian directional hearing

  • Ole Næsbye LarsenEmail author
  • Jakob Christensen-Dalsgaard
  • Kenneth Kragh Jensen


Whereas it is clear from anatomical studies that all birds have complex interaural canals connecting their middle ears, the effect of interaural coupling on directional hearing has been disputed. A reason for conflicting results in earlier studies may have been that the function of the tympanic ear and hence of the interaural coupling is sensitive to variations in the intracranial air pressure. In awake birds, the middle ears and connected cavities are vented actively through the pharyngotympanic tube. This venting reflex seems to be suppressed in anesthetized birds, leading to increasingly lower pressure in the interaural cavities, stiffening the eardrums, and displacing them medially. This causes the sensitivity, as well as the interaural coupling, to drop. Conversely, when the middle ears are properly vented, robust directional eardrum responses, most likely caused by internal coupling, have been reported. The anatomical basis of this coupling is the ‘interaural canal,’ which turns out to be a highly complex canal and cavity system, which we describe for the zebra finch. Surprisingly, given the complexity of the interaural canals, simple models of pipe-coupled middle ears fit the eardrum directionality data quite well, but future models taking the complex anatomy into consideration should be developed.


Zebra finch Budgerigar Intracranial air pressure Eardrum Intracranial cavities Micro-CT scanning 





Hypomedial-orbital tube


Interaural arc


Interaural canal


Inter-bullae passage


Intracranial air


Internally coupled ears


Laser Doppler vibrometry


Medio-orbital canal


Paratympanic organ


Superoantero-orbital sinus


Superolatero-orbital canals



We gratefully acknowledge the financial support from the Danish Council for Independent Research Natural Sciences, the Carlsberg Foundation, and the OTICON Foundation and thank two anonymous reviewers for helpful suggestions to improve the manuscript.

Supplementary material

Supplementary material 1 (mp4 9144 KB)

Supplementary material 2 (mp4 17596 KB)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Department of BiologyUniversity of Southern DenmarkOdenseDenmark
  2. 2.Starkey Hearing Technologies Eden PrairieUSA

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