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:Most of these atlases are based on a single animal (Cannestra et al., 1997; Saleem and Logothetis, 2006; Van Essen, 2002, 2004); while others are based on small samples of 6–12 animals (Black et al., 2001a; Black et al., 2001b; Greer et al., 2002; Vincent et al., 2007).
Category: