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 The stimulus figures were the random polygons originally developed by Attneave and Arnoult (1956) and modified by Cooper (1975; Cooper & Podgorny, 1976), with examples shown in Figure 1.
Category: