Led by Assoc. Prof. Tuukka Ruotsalo, scientists from the the universities of Helsinki and Copenhagen started by getting a generative adversarial neural network to produce hundreds of lifelike computer-generated portraits.
Those facial images were then shown one at a time to a total of 30 test subjects, on a computer screen. Each person was instructed to focus more attention on the faces which they found most attractive, while the electrical activity of their brain was recorded using EEG (electroencephalography).
Machine learning-based algorithms subsequently determined which faces produced the greatest amount of activity for each person, then established which traits those faces had in common. Based on that data, the neural network then proceeded to produce new faces that combined those traits.