Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Previous V1 studies have shown that global visual contours within a cluttered background induce two complementary modulatory effects (Chen et al., 2014; Gilad et al., 2013; Yan et al., 2014): enhancing responses of neurons with RFs lying on the contour (referred to as the contour facilitation) and…
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