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 other potential source of discrepancy in the results between the two studies is the experimental task – in the study of
Todd et al. (2004) the subjects had to specify the position of the local extrema of the depth function on a single scan line while in the present experiment the subjects had…
Category: