title: Smoke and mirrors: Testing the scope of chimpanzees' appearance-reality understanding.
abstract: The ability to make appearance-reality (AR) discriminations is an important higher-order cognitive adaptation in humans but is still poorly understood in our closest primate relatives. Previous research showed that chimpanzees are capable of AR discrimination when choosing between food items that appear, due to the effects of distorting lenses, to be smaller or larger than they actually are (Krachun, Call, & Tomasello, 2009). In the current study, we investigated the scope and flexibility of chimpanzees' AR discrimination abilities by presenting them with a wider range of illusory stimuli. In addition to using lenses to change the apparent size of food items (Experiment 1), we used a mirror to change the apparent number of items (Experiment 2), and tinted filters to change their apparent color (Experiment 3). In all three experiments, some chimpanzees were able to maximize their food rewards by making a choice based on the real properties of the stimuli in contrast to their manifest apparent properties. These results replicate the earlier findings for size illusions and extend them to additional situations involving illusory number and color. Control tests, together with findings from previous studies, ruled out lower-level explanations for the chimpanzees' performance. The findings thus support the hypothesis that chimpanzees are capable of making AR discriminations with a range of illusory stimuli.
authors: Grenfell Campus, Memorial University of Newfoundland, 20 University Drive, Corner Brook, NL A2H 5G4, Canada. Electronic address: ckrachun@grenfell.mun.ca.
authors: Carla
authors: C
authors: Krachun
authors: Brooklyn College, CUNY, 2900 Bedford Avenue, Brooklyn, NY 11210, United States. Electronic address: rlurz@brooklyn.cuny.edu.
authors: Robert
authors: R
authors: Lurz
authors: Georgia State University, Neuroscience Institute, 100 Piedmont Avenue SE, Atlanta, GA 30303, United States; Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, GA 30329, United States. Electronic address: jlcox@emory.edu.
authors: Jamie L
authors: JL
authors: Russell
authors: Georgia State University, Neuroscience Institute, 100 Piedmont Avenue SE, Atlanta, GA 30303, United States; Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, GA 30329, United States. Electronic address: whopkins4@gsu.edu.
authors: William D
authors: WD
authors: Hopkins
mesh_terms: D000818:Animals; D032882:Comprehension / Q000502:physiology*; D005260:Female; D007088:Illusions / Q000502:physiology* / Q000523:psychology; D008297:Male; D002679:Pan troglodytes; D010775:Photic Stimulation / Q000379:methods*; D014796:Visual Perception / Q000502:physiology*
keywords: Appearance–reality discrimination; Chimpanzees; Nonhuman primates; Visual illusions