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:…of NMDAR antagonists have been suggested to be highly useful models of the cognitive impairment in schizophrenia (Stefani and Moghaddam 2002; Abdul-Monim et al. 2007; Grayson et al. 2007; Rodefer et al. 2005; McLean et al. 2009a; Nagai et al. 2009; Young et al. 2009; Snigdha et al. 2010).
Category: