It is the first time fish have demonstrated this ability.
All human faces share the same basic components — two eyes above a nose and mouth. Thus, telling a large number of faces apart is by no means an easy task.
“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,” said Cait Newport, a researcher fellow in the Department of Zoology at Oxford University, in a press release.
Yet, it’s a task to which humans as a whole are highly adept due to the presence of specialized facial recognition structures in our brains. These structures reflect the importance of recognizing faces in our complex social systems.
A study published in the journal Scientific Reports reveals that a species of tropical fish, called the archerfish, is also endowed with this ability. It is the first time fish, which lack the sophisticated visual cortex of primates, have demonstrated an aptitude for distinguishing between human faces.
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Archerfish are well known for knocking insects down from branches by spitting jets of water. So the researchers trained the fish to spit water at a particular human face from a pair of images.
The fish were then presented with the learned face and a series of new faces and were able to correctly choose the face they had initially learned to recognize, even when features like head shape and color were removed from the images. Their peak facial discrimination accuracy was between 77 and 89 percent.
“The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognize human faces. 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,” said Newport.
Previous research has shown that pigeons are also capable of human facial discrimination. However, birds possess neocortex-like brain structures, and it is possible that human facial recognition in pigeons has developed as an adaptation to living among, and regularly interacting with, people.
Fish, on the other hand, do not possess anything resembling a neocortex, and their lack of direct exposure to humans makes it unlikely that they would have evolved special capabilities to recognize human faces.
According to the researchers, their finding suggests “that the visual system of distantly related vertebrates is capable of sophisticated discrimination tasks.”
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