The study, published today in the journal Royal Society: Open Science, is part a series of tests given to the sheep to monitor their cognitive abilities. Because of the relatively large size of their brains and their longevity, sheep are a good animal model for studying neurodegenerative disorders such as Huntington’s disease.

The ability to recognize faces is one of the most important human social skills. We recognize familiar faces easily, and can identify unfamiliar faces from repeatedly presented images. As with some other animals such as dogs and monkeys, sheep are social animals that can recognize other sheep as well as familiar humans. Little is known, however, about their overall ability to process faces.

Researchers from Cambridge’s Department of Physiology, Development and Neuroscience trained eight sheep to recognize the faces of four celebrities 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 (by breaking an infrared beam near the screen); 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 photograph — the celebrity’s face and another face. In this test, 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 recognized the faces, the researchers next showed them the faces at an angle. As expected, the sheep’s performance dropped, but only by about 15% — a figure comparable to that seen when humans perform the task.

Finally, the researchers looked at whether sheep were able to recognize 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 behavior. Upon seeing a photographic image of the handler for the first time — in other words, the sheep had never seen an image of this person before — 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.