From not working to neural networking

Training a neural network involves adjusting the neurons' weights so that a given input produces the desired output (see diagram). Another technique, unsupervised learning, involves training a network by exposing it to a huge number of examples, but without telling it what to look for. In a famous example, when working at Google in 2011, Mr Ng led a project called Google Brain in which a giant unsupervised learning system was asked to look for common patterns in thousands of unlabelled YouTube videos. In essence, training involves adjusting the network's weights to search for a strategy that consistently generates higher rewards.