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:…no impairment of manual motor control has been demonstrated convincingly during simple motor tasks, e.g., paced fist clench (Pascual Leone et al., 1998), finger tapping (Wassermann et al., 1996; Chen et al., 1997), peak force, and acceleration during finger pinch (Muellbacher et al., 2000).
Category: