Change blindness describes the phenomenon when observers fail to notice changes in their visual field. Because the brain has to process so much information it cannot detect every change that occurs. Observers will fail to notice large changes or omissions in their field of vision. One study (Simons & Levin, 1998) that looked at this phenomenon had participants talk to a stranger and were then interrupted by a distraction. The stranger was then replaced by another person during the interruption and half of the participants failed to notice they were talking to another person. The opposite of change blindness is change detection which is when an observer realizes that a change has occurred.