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:…error monitoring, observed consistently in the literature (Carter et al., 1998; Gehring and Knight, 2000; Holroyd and Coles, 2002; Luu et al., 2000; Ullsperger and Von Cramon, 2003), the ERN/Ne can be used to examine the effects of psychoactive substances, such as alcohol (Ridderinkhof et al.,…
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