In differentiate failure due to a difficulty in disengaging attention from failure due to a difficulty in understanding deception, Hughes and Russell (1993) compared the performance of children when an opponent was present with performance when there was no opponent. In the no-opponent conditions, the experimenter had a pile of treats and on each trial placed one of these into one of the boxes while the child had their eyes closed. When the child opened their eyes, they had to indicate to the experimenter which box to open.