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:In humans, this phenomenon is manifested in reduced motivation for work, friends, family, and monetary gain (e.g., Goldstein et al., 2006, 2008; Jones, Casswell, & Zhang, 1995; Nair et al., 1997; SantolariaFernandez et al., 1995).
Category: