Inhibition of return (IOR) refers to the observation that the speed and accuracy with which an object is detected are first briefly enhanced (for perhaps 100-300 milliseconds) after the object is attended, and then detection speed and accuracy are impaired (for perhaps 500-3000 milliseconds). It has been suggested that IOR promotes exploration of new, previously unattended objects in the scene during visual search or foraging by preventing attention from returning to already-attended objects.[1]
IOR is usually measured with a cue-response paradigm, in which a person presses a button when s/he detects a target stimulus following the presentation of a cue that indicates the location in which the target will appear.
IOR was first described by Michael Posner and Yoav Cohen[2], who discovered that, contrary to their expectations, reaction time (RT) was longer to detect objects appearing in previously cued locations. It was subsequently shown that IOR can also be associated with a previously attended object, and under appropriate conditions these two inhibitory effects appear to be additive.