Stickgold conducted extensive studies in 2000 relating sleep to Tetris. After playing several hours each night before bed, 60% of users reported seeing pieces of Tetris as they fell asleep, and even when they are waking up. This is a result of hours of game play, which allows the brain to start creating new neural pathways. This helps the brain recognize patterns easier and perform well with less effort. The brain starts to get trained to search for more images to organize. Players have been found to unconsciously think about ways they can fit objects together in real life, such as visualizing buildings or store shelves. Using his findings to build off of Richard Haier's previous work, he coined the term Tetris Effect. In January 2009, an Oxford University research group headed by Emily Holmes reported that, for healthy volunteers, playing Tetris soon after viewing traumatic material in the laboratory reduced the number of flashbacks to those scenes in the following week. They believe that the computer game may disrupt the memories that are retained of the sights and sounds witnessed at the time, and which are later re-experienced through involuntary, distressing flashbacks of that moment. The group hoped to develop this approach further as a potential intervention to reduce the flashbacks experienced in post-traumatic stress disorder but emphasized that these are only preliminary results. A 2017 study found that people who played Tetris, and similar games such as Candy Crush, while waiting for treatment following traffic accidents had fewer intrusive memories the following week. A study conducted by Mind Research Network in 2009 noticed that girls who played Tetris for 30 minutes over a 3 month period showed a higher function in brain efficiency, and cortical thickness. Prolong Tetris playing may have significant improvement on players' cognitive skills, spatial awareness, and memory retention. Another notable effect is that, according to a Canadian study in April 2013, playing Tetris has been found to treat older adolescents with amblyopia (lazy eye), which was better than patching a victim's well eye to train their weaker eye. Robert Hess of the research team said: "It's much better than patching – much more enjoyable; it's faster, and it seems to work better". Tested in the United Kingdom, this experiment also appears to help children with that problem. Tetris is addictive because of the Zeigarnik effect, that the human brain stores incomplete tasks, and disposes