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:Our zebra finch results seem somewhat in between those obtained by Nagel et al. (2010) and those of van der Aa et al. (2015) for the discrimination between two stimuli of which the temporal parameters were varied compared to the training stimuli.
Category: