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:The most extensive studies have characterized chick brain BgtRs in which three bands with molecular weights of ;50, ;57, and ;67 kDa were observed (ContiTronconi et al., 1985; Gotti et al., 1991, 1992).
Category: