Third paragraph of Intro in original DeepMind paper https://arxiv.org/pdf/1312.5602.pdf
Second paragraph of Intro(5th line) of this project. http://nihit.github.io/resources/spaceinvaders.pdf
They didn't even bother to do something original except for using the RAM state instead of pixel values like the original paper. It's something that's easily doable with the openAI gym. This seems like a course project at stanford.