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:Receptors of virtually every type have been shown to stimulate the production of the phosphoinositides phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P3) and PtdIns-3,4-P2 (Auger et al., 1989; Serunian et al., 1991; Gold and Aebersold, 1994; Gold et al., 1994; Okada et al., 1996).
Category: