In all of these approaches, the spatial layout of the target and the mask does not play a crucial role. However, the spatial layout is of major importance. For example, in an earlier study, a vernier that consisted of two vertical lines slightly offset in the horizontal direction was presented as target (Duangudom, Francis, & Herzog,
2007). Observers indicated the offset direction (left vs. right). When two lines flanked the vernier (i.e., a typical metacontrast mask), B-type masking occurred in accordance with most previous findings and theories (
Figure 1A; Duangudom et al.,
2007). However, when arrays of lines, including the single flanking lines, were presented, strong A-type masking occurred (
Figure 1A). Importantly, the inner contours of the masks (i.e., the innermost flanking lines) were identical in both conditions. Most theories of masking cannot easily explain these results. Duangudom et al. (
2007) proposed that target–mask grouping plays a crucial role. When target and mask are part of one group, masking is strong. When target and mask ungroup, masking is weak (e.g., Duangudom et al.,
2007; Herzog & Fahle,
2002). Furthermore, it was proposed that the very same mechanism also holds true for other visual phenomena such as crowding (Malania, Herzog, & Westheimer,
2007; Manassi, Sayim, & Herzog,
2012; Saarela, Sayim, Westheimer, & Herzog,
2009; Sayim, Westheimer, & Herzog,
2008,
2010,
2011), surround suppression (Saarela & Herzog,
2008), and motion integration (see also nonretinotopic processing; Boi, Öğmen, Krummenacher, Otto, & Herzog,
2009; Öğmen, Otto, & Herzog,
2006).