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:Motion energy filters (MEF; Watson & Ahumada, 1985; Adelson & Bergen, 1985) are built from subunits with separable spatial and temporal receptive fields, as is the case for many V1 simple cells (Robson, 1966; Tolhurst & Movshon, 1975; Field & Tolhurst, 1986; DeAngelis, Ohzawa, & Freeman, 1995; De…
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