Being able to pick a familiar face out of a crowd is important for humans to navigate everyday life. But scientists aren't exactly sure how we do it.
Are our brains hardwired to be able to recognize faces, or do humans learn to identify familiar faces, just as we do with any other object?
To help resolve this puzzle, a team of researchers turned to a very different kind of animal: a tropical fish.
Archerfish, Toxotes chatareus, have simpler brains than humans and lack the part of the brain that scientists associate with facial recognition in humans. And they have "no evolutionary need to recognise human faces," the study's first author, Cait Newport, points out in a news release.
And yet these fish can do it.
"This does start to suggest that there's nothing special about human faces, and that they can be treated as any other object and still recognized," Dr. Newport, the Marie Curie Research Fellow in the Department of Zoology at Oxford University, told The Washington Post.
Archerfish have an uncanny ability to spit. Yes, that's right, these fish shoot jets of water out of their mouths to knock prey, like insects, out of the air. Because of their accuracy, these spitting swimmers were perfect candidates for this experiment.
The researchers first trained the fish to spit at a particular face displayed on a screen. When they got it right, they were rewarded with food.
Once the fish were trained to spit at a face, the researchers mixed that face in among as many as 44 others in sequence. And the fish didn't spit randomly: 81 percent of the time they spat at the correct face.
The scientists even tried changing the image to black and white and standardizing head shape so there were fewer distinctions between faces. Then, the fish picked the right face 86 percent of the time. The results are reported in a paper published Tuesday in the journal Scientific Reports.
"Being able to distinguish between a large number of human faces is a surprisingly difficult task," Newport said in the news release, "mainly due to the fact that all human faces share the same basic features. All faces have two eyes above a nose and mouth, therefore to tell people apart we must be able to identify subtle differences in their features. If you consider the similarities in appearance between some family members, this task can be very difficult indeed."
"This is just the scratching of the surface," Newport told The Washington Post. "We may even find that fish aren't able to do it in other conditions."
"The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognise human faces," she said in the news release. "Humans may have special facial recognition brain structures so that they can process a large number of faces very quickly or under a wide range of viewing conditions."