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:Electroretinograms (ERGs) were recorded under controlled conditions that conformed to the standards of the International Society of Clinical Electrophysiology of Vision.(15) Briefly, photopic ERGs were elicited by a single flash or a 30-Hz flicker stimulus of red light under light-adapted conditions (cone-isolated responses); a dim blue flash under darkadapted conditions (30 minutes) was used for the rod-isolated ERGs (rod-isolated responses); and a bright white flash (intensity of 1.
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