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 vivo recordings show that the firing rate of Purkinje cells is modulated during behavior within a range as high as 250 spikes per second (sp/s) and as low as 5 sp/s (Lisberger and Fuchs 1978).
Category: