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:…complexity, distractor number, speed, and interobject distance have been shown to affect capacity (Alvarez & Franconeri, 2007; Bettencourt & Somers, 2009; Franconeri, Alvarez, & Enns, 2007; Horowitz et al., 2007; Tombu & Seiffert, 2011; Vogel et al., 2005; Xu & Chun, 2006; Zanto & Gazzaley, 2009).
Category: