Perception of a visual stimulus depends on its surrounding context; a well-known example of contextual modulation is surround suppression, wherein the perceived contrast of a stimulus is reduced by the presence of surrounding stimuli, compared to when it is viewed in isolation (Cannon & Fullenkamp,
1991; Chubb, Sperling, & Solomon,
1989; Ejima & Takahashi,
1985; Petrov & McKee,
2006; Snowden & Hammett,
1998; Xing & Heeger,
2000,
2001; Yu, Klein, & Levi,
2001). Studies in animal models have shown that neurons in primary visual cortex (V1) typically show reduced spike rates in response to a stimulus presented with a surround, compared to when a stimulus appears in the receptive field alone (Bair, Cavanaugh, & Movshon,
2003; Cavanaugh, Bair, & Movshon,
2002a,
2002b; DeAngelis, Freeman, & Ohzawa,
1994; Ichida, Schwabe, Bressloff, & Angelucci,
2007; Shushruth, Ichida, Levitt, & Angelucci,
2009; Shushruth et al.,
2013; Walker, Ohzawa, & Freeman,
1999). Similar results have been observed in human V1 using functional magnetic resonance imaging (Chen,
2014; Flevaris & Murray,
2015; Joo, Boynton, & Murray,
2012; Nurminen, Kilpelainen, Laurinen, & Vanni,
2009; Pihlaja, Henriksson, James, & Vanni,
2008; Williams, Singh, & Smith,
2003; Zenger-Landolt & Heeger,
2003), suggesting that a reduction in the V1 response may underlie the reduction in perceived contrast observed with surround suppression.