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:Finally, pigeons may even be superior to humans in their capacity to mentally rotate visual information, as they show no increase in reaction time when judging the identity of stimuli presented at increasingly different angular orientations, whereas humans do (Hollard & Delius, 1982).
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