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:…time constants of 280 ns and 300ms led to a unidirectional model of the early photocycle with two different hK states:
hR1 hn ¡ hKE ¡ hKL ¡ hL ¡ · · ·¡ hR
The hKE (early K) and hKL (late K) states were named by analogy with the substates of the early bR photocycle (Dioumaev and Braiman, 1997b).
Category: