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 is consistent with the findings of previous studies of the neural substrates of sleep-dependent enhancement of motor sequence learning (Walker et al., 2005a; Albouy et al., 2008; Debas et al., 2010).
Category: