Visual search is not only challenged by the inhomogeneity of the visual system but is also often complicated by occlusions (e.g., a seagull that flies behind a pier and is therefore momentarily out of sight). How does our visual system keep track of (temporally) occluded objects? For instance, how do we know that the seagull that disappeared behind one side of the pier is the same seagull that appears at the other side? Interestingly, this
object correspondence problem already exists on a microlevel of visual perception. Since processing of visual input is suppressed during saccadic eye movements as well as eye blinks (e.g., Burr et al.,
1994; Matin,
1974; Thiele et al.,
2002), short—internally triggered—occlusions of visual input occur several times a second. The most important cue for our visual system in solving this object correspondence problem is
spatiotemporal continuity (e.g., Cox et al.,
2005; Flombaum, Scholl, & Santos,
2009; Li & DiCarlo,
2008,
2010; Schneider,
2013; Schreij & Olivers,
2013). Spatial as well as temporal information about an object before its occlusion allow the visual system to predict its location and time of reappearance (e.g., when and where a seagull will reappear behind the pier). If this prediction is violated (e.g., by a seagull appearing behind the fish and chips shop instead of the pier), object correspondence is not established because it is most likely a different object. The prominent role of spatiotemporal continuity in object persistence is evident from behavioral studies (e.g., Cox et al.,
2005; Schreij & Olivers,
2013) as well as neurophysiological studies (e.g., Li & DiCarlo,
2008,
2010). For instance, Schreij and Olivers (
2013) demonstrated that visual search benefits due to repetition of the target location from a previous trial disappeared if the spatial or temporal continuity of the search display's motion trajectory were disrupted. Object persistence across saccades seems to be mainly driven by spatiotemporal continuity as well. For example, Cox et al. (
2005) demonstrated that humans are able to associate (slightly) different objects across saccades while the spatiotemporal continuity of the situation was preserved. Moreover, Li and DiCarlo (
2008) demonstrated in a single cell study with rhesus monkeys that under spatiotemporal continuity even completely different objects can be associated across saccades. An important mechanism that contributes to the establishment of object continuity across saccades is predictive remapping, which has been demonstrated on a behavioral as well as neuronal level (Duhamel, Colby, & Goldberg,
1992; Rolfs, Jonikaitis, Deubel, & Cavanagh,
2011). In retinotopic organized brain areas, the activity of neurons is increased if a planned saccade will bring a stimulus into their receptive fields (Duhamel et al.,
1992). It has been shown on a behavioral level that discrimination performance increases up to 75 ms at the future, predicted retinotopic location of the saccade target, the fovea (for further discussion of location prediction and its possible relationship to feature prediction, see Herwig and Schneider,
in press). Several recent behavioral studies (Boi, Ögmen, Krummenacher, Otto, & Herzog,
2009; Hein & Cavanagh,
2012; Hunt & Cavanagh,
2011; Szinte & Cavanagh,
2011) revealed that spatiotopic coordinates seem to be more important than retinotopic coordinates in establishing object continuity across saccades. Hunt and Cavanagh (
2011) demonstrated that if object continuity of a presaccadically presented Landolt C oriented to the left or right was disrupted by a presaccadic mask, a mask at the predicted/remapped location was much more effective than a mask at the presaccadic spatial location of the target. Moreover, the work by Szinte and Cavanagh (
2011) indicates that space constancy is a result of predictive remapping and is obtained for only a few attended objects. Participants saw two dots: one before and one after the saccade. The second dot was displaced about 3° vertically from the first dot, but due to the saccade the second dot was additionally displaced by 10° horizontally from the first dot. Participants perceived apparent motion across the saccade to be stronger vertically than horizontally, indicating that the visual system corrects for the horizontal displacement due to the saccade. Furthermore, Boi et al. (
2009) demonstrated that nonretinotopic processing plays an important role in motion perception and visual search. To summarize, spatiotemporal continuity has proven to be an important factor in establishing object persistence across frequently occurring interruptions of visual input, particularly saccadic eye movements.