Inhibition of Return after Color Singletons

When we look around, only a part of the visual signals arriving at our retinae at each moment in time is selected for in-depth processing. This form of selectivity is called visual attention. Visual attention has many different purposes. Selection can gate access of information to perception (Scharlau, 2002), memory (Duncan & Humphreys, 1989), or motor control (Allport, 1989). Corresponding to its multiple purposes, visual attention is also influenced by many different factors, such as the properties of the stimulus (Itti, Koch, & Niebur, 1998) and the goals of the human observer (Folk, Remington, & Johnston, 1992). One important factor is the observer’s memory trace of the visual information that has been selected in the recent past. One primitive form of such memory has been called inhibition of return (IOR): It has been demonstrated that shifting visual attention toward one position in space delays a second subsequent attention shift to the same position at a later point in time (Posner & Cohen, 1984; Taylor & Klein, 1998). This phenomenon is called IOR because it is supposed to reflect the human resistance to select information from positions that have recently already been inspected by a covert shift of attention (Posner & Cohen, 1984). In this context, a covert shift of attention is a shift of attention without the eyes, whereas an overt shift would be accompanied by an eye movement (Posner, 1980).