A search for search asymmetry in chimpanzees (Pan troglodytes).

Two chimpanzees and two humans were trained on visual search tasks with several sets of geometric forms composed of 1 and 2 elements (graphemes). When the double-grapheme item was the target and single grapheme item was the distractor, both chimpanzees and humans searched the target quickly irrespective of the display size. On the other hand, when the single-grapheme item was the target and double-grapheme item was the distractor, they showed an increase in response times as a function of the display size on some sets of stimuli. These results were considered as evidence for search asymmetry by chimpanzees.