Monkeys react differently to familiar and unfamiliar faces. An article about this is published in Proceedings of the Royal Society B: Biological Sciences.
Researchers from the American Johns Hopkins University studied how the behavior of monkeys differs from visitors and zookeepers. They focused on a dozen large primates living at the Lincoln Zoo in Chicago. They were shown pictures of familiar and unfamiliar faces on a touch screen.
Two photographs were displayed for 30 seconds, after which both disappeared, and one was replaced by a dot, the touch of which led to a sound signal and the issuance of fruit.
“We found that, on average, subjects were about 11 percent slower to touch a point when it replaced a familiar face,” the authors write. If the face was wearing a medical mask, the difference was 9 percent. The researchers conclude that the attention of animals was riveted primarily to a stranger. The same thing scientists have previously noticed in human babies: first of all, they pay attention to strangers.
Moreover, if the faces expressed surprise, there was almost no difference in reactions to familiar and unfamiliar people.