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:…and Sieving 1995; Frishman et al. 1996), but during rod vision, neural adaptation is apparent at light intensities too low to cause adaptation of rod phototransduction (Barlow and Levick 1969; Enroth-Cugell and Shapley 1973; Frishman and Sieving 1995; Naarendorp et al. 2001; Saszik et al. 2002).
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