Inhibition of return (IOR) is a cognitive research phenomenon in which individuals typically respond (by recognizing, orienting, directing attention, etc.) at a slower rate when viewing the stimuli at the same location where an irrelevant stimulus was previously located.
IOR was first identified by Michael Posner and Yoav Cohen. The theory behind IOR proposes that when responding to a stimulus individuals are more likely to orient towards novelty (in this case responding faster and more accurately to a stimulus not associated with a previously irrelevant stimulus.)
For instance in out modern world many machines beep when somethings is wrong, so much so that it is easy to tune out the beeping and puzzle over what is wrong in your car or with your computer. However, while driving a car a novel noise such as a siren, or a strange noise from the engine will immediately draw your attention.