What is binocular vision for? A birds' eye view

Graham Martin

Research output: Contribution to journalArticle

86 Citations (Scopus)


It is proposed that with the possible exception of owls, binocularity in birds does not have a higher order function that results in the perception of solidity and relative depth. Rather, binocularity is a consequence of the requirement of having a portion of the visual field that looks in the direction of travel; hence, each eye must have a contralateral projection that gives rise to binocularity. This contralateral projection is necessary to gain a symmetrically expanding optic flow-field about the bill. This specifies direction of travel and time to contact a target during feeding or when provisioning chicks. In birds that do not need such control of their bill, binocular field widths are very small, suggesting that binocular vision plays only a minor role in the control of locomotion. In the majority of birds, the function of binocularity would seem to lie in what each eye does independently rather than in what the two eyes might be able to do together. The wider binocular fields of owls may be the product of an interaction between enlarged eyes and enlarged outer ears, which may simply prevent more lateral placement of the eyes.
Original languageEnglish
Pages (from-to)1-19
Number of pages19
JournalJournal of Vision
Issue number11
Publication statusPublished - 1 Jan 2009


  • optic flow-field
  • stereopsis
  • binocular vision
  • foraging
  • lateral vision
  • eye movements
  • contralateral vision
  • visual fields
  • birds


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