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:Additional rodent work investigating the effects of bilateral cortical lesions shortly following birth demonstrates a difficulty for early-cortical lesioned male, but not female, rodents to discriminate rapidly presented tones (<350 ms), while both sexes could reliably discriminate tones presented at longer interstimulus intervals (ISIs) (Herman et al., 1997).
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