What counts for 'counting'? Chimpanzees, Pan troglodytes, respond appropriately to relevant and irrelevant information in a quantity judgment task

► Animals discriminate between quantities, but do they know what 'counts' in such discriminations? ► Four chimpanzees chose between two arrays of food items. ► Sometimes, individual items were seen more than once. ► These re-presentations of items needed to be ignored for accurate judgments of array quantities to occur. ► Chimpanzees selected the correct arrays with more food despite these attempts to bias their judgments.