Cambridge scientists have trained sheep to recognise faces of British actress Emma Watson and former US President Barack Obama, in a bid to demonstrate that the animals can be taught to recognise human faces from photographic portraits.
The study is part of a series of tests given to the sheep to monitor their cognitive abilities.
Due to their relatively large size of their brains and their longevity, sheep are a good animal model for studying neuro-degenerative disorders such as Huntington's disease, according to scientists from the University of Cambridge in the UK.
Researchers trained eight sheep to recognise the faces of four celebrities - Fiona Bruce, Jake Gyllenhaal, Barack Obama and Emma Watson - from photographic portraits displayed on computer screens.
Training involved the sheep making decisions as they moved around a specially-designed pen. 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.
If they chose the wrong photograph, a buzzer would sound and they would receive no reward. Over time, they learn to associate a reward with the celebrity's photograph.
After training, the sheep were shown two photographs the celebrity's face and another face. Sheep correctly chose the learned celebrity face eight times out of ten.
In these initial tests, the sheep were shown the faces from the front, but to test how well they recognised the faces, the researchers next showed them the faces at an angle. As expected, the sheep's performance dropped, but only by about 15 per cent - a figure comparable to that seen when humans perform the task.
Finally, the researchers looked at whether sheep were able to recognise a handler from a photograph without pre-training. The handlers typically spend two hours a day with the sheep and so the sheep are very familiar with them.
When a portrait photograph of the handler was interspersed randomly in place of the celebrity, the sheep chose the handler's photograph over the unfamiliar face seven out of ten times. During this final task the researchers observed an interesting behaviour. Upon seeing a photographic image of the handler for the first time the sheep did a 'double take'.
The sheep checked first the (unfamiliar) face, then the handler's image, and then unfamiliar face again before making a decision to choose the familiar face, of the handler.
"Anyone who has spent time working with sheep will know that they are intelligent, individual animals who are able to recognise their handlers," said Professor Jenny Morton, who led the study published in the journal Royal Society: Open Science.
"We've shown with our study that sheep have advanced face-recognition abilities, comparable with those of humans and monkeys," Morton said.