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:The average magnitude of the NBR increases with increasing stimulus intensity and duration (Klingner et al., 2010; Shmuel et al., 2002), suggesting that NBR reflects neuronal inhibition required to optimise task performance, by reducing sensitivity and allocation of processing resources to the unattended or irrelevant part of the sensory field.
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