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:All speech was recorded using a head-mounted microphone while the participants were connected to a Finometer [4], a device that enables continuous monitoring of CV parameters in a non-intrusive manner, i.e., by using a finger-cuff.
Category: