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:This hypothesis was based on the evidence in the literature for significantly worse performance of adult CI users compared with adults with NH in the perception of pitch, timbre, and in the recognition of familiar melodies, as measured with music perception tests (Brockmeier et al., 2011; Kang et al., 2009; Looi, McDermott, McKay, & Hickson, 2008).
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