Over the course of human history, people"s eyes have changed so that they can better gauge depth and height, but until now the cause of this has been unknown.
However, a new study has helped to shed some light on this process by using owls as a model.
The research reveals the advantage of stereopsis, which is commonly known as stereovision, has is the ability to decipher between objects and background, not in perceiving absolute depth.
The findings were published in an edition of the Journal of Vision and conducted at RWTH Aachen in Germany and Radboud University in the Netherlands.
By determining that owls see in stereo much like humans do, the experts were able to uncover how depth perception came into existence during the course of evolution.
For the study, lead author Dr Robert van der Willigen, of the Donders Institute for Brain, Cognition and Behavior at Radboud, examined two trained barn owls and conducted a series of six behavioural experiments similar to those used on humans.
Using computer-generated binocular random-dot patterns to measure stereo performance, he found that an owl"s ability to discriminate random-dot stereograms is parallel to that of humans, in spite of the owl"s relatively small brain.
He explained that the results provided "unprecedented data" about stereovision, and debunk the long-held belief that the evolutionary advantage of seeing in stereo is rooted in depth vision.
"The reason why studying owl vision is helpful is that, like humans, owls have two frontally placed eyes. As a result, owls, like humans, could appreciate the 3-dimensional shape of tangible objects through simultaneous comparison of the left and right eye," he added.
According to Dr Van der Willigen, he hopes that future studies will take into account the fact that human or primate vision is not the only way to examine the stereovision experience.
"My present work on the owl highlights underappreciated, but fundamental aspects of stereopsis. Hopefully, it will encourage scientists to investigate other animal species," he concluded.
by Emily Tait