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:Moreover, cognitive abilities are usually positively related to gains from mnemonic training (Kliegl et al., 1990; Lindenberger et al., 1992; Verhaeghen and Marcoen, 1996).
Category: