This particular test is an imitation of Raven's Progressive Matrices, which measures working memory (WM). WM is the amount of information "chunks" an individual can work with in their short term memory. For an average person it's "7+-2" or 5-9 "chunks".

The patterns you see on the test introduce progressively more and more changes, until you are getting beyond 9 changes a piece at 120+ IQ. Let me know if you have any questions.