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The monkeys started off by looking at a black and white texture - to keep it “non-biased,” says Ponce - that evolved, ever so slightly, as the neural network responded to the changes that made its neurons fire the most.
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"We found that these cells were responding better to … the dream versions of these natural-world pictures." On the right are the "natural images" that the scientists used to identify the face neurons in the first place. The images on the left are what the GAN produced in response to the activity of face-recognizing neurons.
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“They looked like objects in the world that were not in the world,” says Ponce. As the images evolved, one thing became clear: These cells are into some weird shit. In Ponce’s experiments, the discriminator was the monkey neuron, hooked up to the GAN, which burst with activity if it approved of the image it saw. These generative adversarial networks, or GANs, evolve images based on input from a “discriminator” that determines what’s good and what’s not. used to generate imaginary but uncannily realistic images like DeepFakes and other creepy art. To do the impossible, Ponce and his team took advantage of a powerful new tool. Previously, researchers investigated this by showing subjects countless images to find out what was best at turning their neurons on - an impossible task, since there are an infinite number of images to show. Scientists trying to understand this aspect of our visual systems are trying to understand how it is we evolved to not only see but also recognize complex images like faces, and also objects, places, and animals. “We’ve been stuck with this problem for decades,” first author Carlos Ponce, Ph.D., a neuroscientist at Washington University School of Medicine in St. "They looked like objects in the world that were not in the world." Is it a certain eyes-nose-mouth combination that triggers its frenzy? A particular arrangement of colors? What is a face, to a neuron? In a groundbreaking Cell study, scientists found out through an unusual approach: They asked the cells themselves. For a long time, scientists have pondered what it is, exactly, that tickles the very particular fancies of these neurons. Every time you look at a face, a group of neurons behind your ears goes wild with excitation.