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 susceptibility to proactive interference after hippocampal damage has already been reported by others [Owen and Butler, 1981; but for different results, see BeasonHeld et al. (1999) and Zola et al.
Category: