The proportion of volunteers that showed significant activation with increasingly more time, in each task. The figure displays significant whole-brain activation to the selective attention and motor imagery tasks at one of five time intervals in the same areas where activation was observed for the duration of the entire task. Each interval contains an added on/off trial, from one, at the start of each session, to five, at the end. At the end of each scanning session, 100 versus 87% of volunteers showed significant activation for each task, respectively.