1. The person concept in monkeys (Cebus apella);D'Amato;J. Exp. Psychol. Anim. Behav. Proc.,1988
2. Rapid categorization of natural images by rhesus monkeys;Fabre-Thorpe;Neuroreport,1998
3. Natural concepts in pigeons;Herrnstein;J. Exp. Psychol. Anim. Behav. Proc.,1976
4. Complex visual concept in the pigeon;Herrnstein;Science,1964