Recognizing faces was taken to need a cortex of the kind mammals have, and fish do not have one. hunt by spitting a jet of water, and that spit can serve as an answer. So photographs of faces were put in front of them. What did they do?
They learned the face. On each trial the fish saw two photographs and got food for hitting the one it had been taught, and they told dozens of faces apart. Then the researchers took away the shortcuts: converted the images to gray and matched the shape of the head, and the fish went on succeeding. So accurate visual recognition does not require .
In humans and in monkeys there is a region of cortex specialized for recognizing faces, so the assumption was that the task demands a structure of that kind.
Archerfish hunt insects by spitting a jet of water, and the researchers used that spit as the answer. On each trial two photographs of faces were shown, and the fish got food for hitting the one it had been taught.
They told dozens of faces apart. But success like that can still be explained by a shortcut, spotting a bright patch for instance, or the shape of a head.
So the researchers set about : they converted the images to gray and matched the shape of the head, and the fish went on succeeding. Which is to say this does not require a mammalian cortex. The fish went through intensive training against two-dimensional photographs, and the study does not show that they recognize people naturally.
wat. Archerfish learned to spit at one photographed face and kept identifying it with no color, no brightness and no distinctive head outline.
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The ability separates recognizing a complex pattern from the particular brain structure humans use for faces.
How do we know?
In two choice experiments the fish were trained to spit at a rewarded face, and tested against 44 color faces and then against 18 faces processed to remove simple cues.
What is still unknown
The fish went through intensive training against two-dimensional photographs. This is discrimination rather than understanding: it does not show they recognize people naturally, or grasp that a face belongs to somebody.
Learn something?
Where to next
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