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Abstract Oculomotor inhibition of return (IOR) is believed to facilitate scene scanning by decreasing the probability that gaze will return to a previously fixated location. This "foraging" hypothesis was tested during scene search and in response to sudden-onset probes at the immediately previous (one-back) fixation location. The latencies of saccades landing within 1° of the previous fixation location were elevated, consistent with oculomotor IOR. However, there was no decrease in the likelihood that the previous location would be fixated relative to distance-matched controls or an a priori baseline. Saccades exhibit an overall forward bias, but this is due to a general bias to move in the same direction and for the same distance as the last saccade (saccadic momentum) rather than to a spatially specific tendency to avoid previously fixated locations. We find no evidence that oculomotor IOR has a significant impact on return probability during scene search.
Keywords Eye movement * Real-world scenes * Visual search * Inhibition of return * Fixation duration * Saccadic momentum
When searching a cluttered scene for a hard-to-find object, we need to focus our eyes on each part of the scene in turn. The sequence of fixations (when the eyes are still) and saccades (ballistic movements of the eyes) provides insight into how a scene is processed in visual search (Findlay, 2004; Henderson, Chanceaux & Smith, 2009; Henderson & Smith, 2009; Malcolm & Henderson, 2010; Yarbus, 1967; Zelinsky, Rao, Hayhoe & Ballard, 1997). Each saccadic eye movement requires that the next candidate location be selected from a range of potential target locations. An optimum search strategy would be to visit each candidate location only once to check whether the search target is present, before moving on to the next candidate location (Melcher & Kowler, 2001; Najemnik & Geisler, 2005). This strategy would require a mechanism for keeping track of visited locations (Peterson, Kramer,Wang, Irwin&McCarley, 2001). One mechanism proposed to fulfill this purpose is inhibition of return (IOR).
Classically, IOR has been defined as an increase in reaction time (RT) to a target appearing at a previously attended location (Posner & Cohen, 1984). IOR is traditionally observed in attentional cuing paradigms, and both its behavioral and neural properties have been extensively studied (see Klein, 2000, and Wang...