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:…and morphogens contained within the E-CSF (such as FGF2, apolipoproteins, retinol binding protein, retinol and low density lipoproteins) in controlling initial neurogenesis and neuroepithelial cell proliferation and survival (Martin et al., 2006; Bachy et al., 2008; Parada et al., 2008, in press).
Category: