title: Summation and numerousness judgments of sequentially presented sets of items by chimpanzees (Pan troglodytes).
abstract: Summation and numerousness judgments by 2 chimpanzees (Pan troglodytes) were investigated when 2 quantities of M&Ms were presented sequentially, and the quantities were never viewed in their totality. Each M&M was visible only before placement in 1 of 2 cups. In Experiment 1, sets of 1 to 9 M&Ms were presented. In Experiment 2, the quantities in each cup were presented as 2 smaller sets (e.g., 2 + 2 vs. 4 + 1). In Experiment 3, the quantities were presented as 3 smaller sets (e.g., 2 + 2 + 3 vs. 3 + 4 + 1). In Experiment 4, an M&M was removed from 1 set before the chimpanzees' selection. In Experiments 1 and 2, the chimpanzees selected the larger quantity on significantly more trials than would be predicted by chance. In Experiments 3 and 4, 1 chimpanzee performed at a level significantly better than chance. Therefore, chimpanzees mentally represent quantity and successfully combine and compare nonvisible, sequentially presented sets of items.
authors.affiliation: Department of Psychology, Georgia State University, Decatur 30034, USA. mjberan@yahoo.com
authors.forename: M J
authors.initials: MJ
authors.lastname: Beran
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002755:Choice Behavior; D003071:Cognition; D005260:Female; D008297:Male; D008433:Mathematics; D002679:Pan troglodytes / Q000523:psychology*; D012691:Serial Learning