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:angles between 0o and 60o (Durgin, Li & Hajnal, 2010). Durgin, Li and Hajnal (2010) argued that although verbal estimates and non-verbal angle bisection reports provided clear evidence that near surfaces appeared steeper than they were, free hand measures showed good calibration to actual surface orientation because they are calibrated by visuomotor experience.
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