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:PFC patients and controls did not differ with respect to the amount of time spent making the first move on each tower, a finding consistent with previous studies (Andres & Van der Linden, 2001; Goel & Grafman, 1995; Jacobs & Anderson, 2002; Owen et al., 1990; Rushe et al., 1999).
Category: