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:This noise stems from pulsatile motion of large arteries in the direct vicinity of the brainstem as well as from the flow of cerebro-spinal fluid (CSF) (Harvey et al., 2008; Klose et al., 2000).
Category: