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:When the discrepancy between cues was intentionally manipulated to be large, switching back has been observed experimentally (Cheng 1988; Cheng et al. 1987; Chittka and Geiger 1995a, 1995b; Etienne et al. 1990; Healy and Hurly 1998; Kamil and Jones 1997; Mackintosh 1973; also see Cheng et al. 2007).
Category: