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:Previous investigations illustrated that a single afferent potential is sufficient to trigger the reflex (Krans and Chapple 2005), that spontaneous afferent potentials that occur during reflex activation of the motoneurons do not reset the reflex (Chapple and Krans 2004), and that the excitatory synaptic potentials that depolarize postural motoneurons during the initial reflex phase have relatively little variability (Krans and Chapple 2005).
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