Visual performance can be strongly modulated by contextual elements. For example, in foveal vision, vernier offset discrimination deteriorates when the vernier is flanked by neighboring lines (e.g., Badcock & Westheimer,
1985; Levi, Klein, & Aitsebaomo,
1985; Westheimer & Hauske,
1975; Westheimer, Shimamura, & McKee,
1976; see also Flom, Weymouth, & Kahneman,
1963; Jacobs,
1979; Toet & Levi,
1992). On a neural level, local interactions between a target and its context are often proposed to explain contextual modulation. For example, neurons dedicated to vernier discrimination are thought to be inhibited by the flankers (e.g., Westheimer & Hauske,
1975; see also Bjork & Murray,
1977). In peripheral vision, the deleterious influence of flankers (“crowding”) is often explained by spatial pooling: neural activity corresponding to both the target and the flankers is integrated and, thus, feature identification is impaired (e.g., Baldassi & Burr,
2000; Parkes, Lund, Angelucci, Solomon, & Morgan,
2001; Pelli, Palomares, & Majaj,
2004; Wilkinson, Wilson, & Ellemberg,
1997).