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:Furthermore, adjustment of the K+ current resulted in a linear depolarization of
spike threshold, another commonly observed feature of the D-current (Bekkers and Delaney 2001; Dodson et al. 2002; Shen et al. 2004; Guan et al. 2007; Shu et al. 2007a).
Category: