Archerfish Can Learn to Recognize Human Faces

Archerfish can learn to tell human faces apart, even without a neocortex, showing that complex visual recognition can be learned by a fish.

Biology

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Archerfish are famous for knocking insects from above the water with remarkably accurate jets of water, but their visual skills go beyond aiming. In a 2016 study, researchers trained archerfish to distinguish between human face images and then tested whether they could recognize the learned face among many unfamiliar faces. In one experiment, the fish were tested against 44 other faces and successfully discriminated the trained face. A second experiment used 18 grayscale faces while standardizing brightness, color, and head shape, reducing the chance that the fish were simply using easy visual clues. The fish still performed well, reaching peak discrimination accuracy of about 77 to 89 percent during testing. The result was notable because fish do not have the neocortex associated with human face recognition. The study therefore supported the idea that at least some aspects of face recognition can be learned through general visual processing rather than requiring a specialized mammalian brain structure. It does not show that archerfish recognize faces in exactly the same way humans do, but it does show that a relatively small and very different vertebrate brain can learn surprisingly sophisticated visual distinctions. Later work also found that archerfish can recognize familiar objects when their viewing angle changes, adding to evidence that their visual system can perform more than simple picture matching.

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