However, their ability to recognize human faces from photos alone is novel.
When they were tested if they could perform without the rewards, the sheep were able to recognize the celebrities faces eight out of 10 times, Sky News reported. Whenever the sheep correctly chose the option, the testing got popped out with a treat. (A sheep might have had to select Emma Watson vs. a football helmet or gas lamp, for instance.) The third test pitted the sheep's celebrity targets against unfamiliar humans.
To challenge the sheep even further, scientists showed them the same celebrities in photos captured from a different, tilted angle.
The animal's "ability to learn to recognise a person from a 2D (two-dimensional) photograph was surprising, since this requires complex brain processing", said Morton.
At one end of the pen, they would see two photographs displayed on two computer screens and would receive a reward of food for choosing the photograph of the celebrity, by breaking an infrared beam near the screen.
Sheep have been known to pick out pictures of individuals in their flock, and even familiar handlers (SN: 10/6/12, p. 20). The sheep were still able to choose the correct person, showing that they weren't simply memorizing what a 2D photo looks like, but instead were understanding the 3D idea of a human head. In follow-up experiments, the authors of the new study had the sheep once again chose between images of celebrities or strangers.
The researchers found that sheep can recognize both familiar and unfamiliar human faces.
"Sheep are long-lived and have brains that are similar in size and complexity to those of some monkeys".
"Humans do tend to underestimate the ability of sheep", Morton said by email.
The study feeds into ongoing research on treating neurodegenerative diseases such as Huntington's, in which face perception can be impaired.
"If this is the case, we can use the test to measure the beneficial effect of new treatments".