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:Stimuli surfaces were irregular-shaped wooden boards manually
placed on a metal slope-presentation device that allowed the experimenter to quickly and accurately set the wooden board to a predetermined angle (see Durgin, Li &
Hajnal, 2010; Li and Durgin, 2009).
Category: