The effects of Portal 2 and Lumosity on cognitive and noncognitive skills
Valve playtests the shit out of their games. A lot of <i>Portal</i>'s theming is based on their extensive testing culture and the ways they've developed to manipulate the player through testing. For example, the Weighted Companion Cube came about because they wanted a level where you solve puzzles while carrying an object. But the playtesters kept leaving the damn object behind. So Valve's solution was to tell them it was a "character" they had to care for.