Journal of Comparative Psychology 1999, Vol. 113, No. 2, 137-148 Copyright 1999 by the American Psychological Association, Inc. 0735-7036/99/S3.00 Strategies Used to Combine Seriated Cups by Chimpanzees (Pan troglodytes), Bonobos (Pan paniscus), and Capuchins (Cebus apella) Julie Johnson-Pynn, Dorothy M. Fragaszy, and Elizabeth M. Hirsh University of Georgia Patricia M. Greenfield University of California, Los Angeles Karen E. Brakke Georgia State University The authors investigated strategies used to combine seriated cups by apes (Pan troglodytes and P. paniscus) and monkeys (Cebus apella) using a protocol reported in P. M. Greenfield, K. Nelson, and E. Saltzman's (1972) study with children. It was hypothesized that apes would exhibit more hierarchical combinations of cups than monkeys, given apes' language capacity, and that apes would seriate the cups more efficiently than monkeys. As predicted, apes made many structures with the cups using a variety of strategies, and monkeys rarely combined the cups. After a training phase to orient monkeys to the task, the 2 genera did not differ in the strategies used to combine the cups or in efficiency in seriating the cups. Success in this task suggests that sensorimotor versions of hierarchically organized combinatorial activity are well within apes' and monkeys' abilities. The organization of manual activity has been studied extensively in human children. Piaget (1954) pioneered the study of motor activity as an expression of cognitive function by identifying programs of action in the child's manipulation of objects. More recently, neo-Piagetian (Case, 1985, 1991) and information-processing theorists (e.g., Siegler, 1986, 1989) have examined the development of rule-guided behavior or strategies within this context. Others have explored the coordination of movement sequences, including the child's self-monitoring of the consequences of his or her actions in service of a goal (e.g., spoon use; Connolly & Dalgleish, 1989). We were interested in analyzing the organization of movement sequences as an aspect of planning in nonhuman primates by comparing combinatorial manipulation of ob- jects in two species of apes, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), and one species of monkey, the tufted capuchin (Cebus apella). The task of combining a set of seriated cups was chosen for this purpose. Greenfield, Nelson, and Saltzman (1972) explored chil- Julie Johnson-Pynn, Dorothy M. Fragaszy, and Elizabeth M. Hirsh, Department of Psychology, University of Georgia; Karen E. Brakke, Department of Psychology, Georgia State University; Patricia M. Greenfield, Department of Psychology, University of California, Los Angeles. Karen E. Brakke is now at the Department of Psychology, Morris Brown College. This work was supported by Grant HD06016 from the National Institute of Child Health and Human Development. We wish to acknowledge Duane Rumbaugh, Sue Savage-Rumbaugh, and the staff at the Language Research Center for their support in data collection for the chimpanzees and bonobos in this study. Correspondence concerning this article should be addressed to Julie Johnson-Pynn, Department of Psychology, University of Georgia, Athens, Georgia 30602. Electronic mail may be sent to jpynn@egon.psy.uga.edu. dren's development of rule-guided behavior in assembling seriated cups. They were specifically interested in the emergence of hierarchical organization of manual activity. Hierarchical organization occurs when lower level units are combined into higher level or more complex units. Green- field et al. identified three strategies in children's manipula- tion of nesting cups (see Figure 1). The strategies differ in the degree to which they necessi- tate hierarchical organization of sequential actions with the cups. The simplest way to combine the cups (the "pairing method") involves nesting or stacking two cups. In the "pot strategy," two or more cups are placed one at a time into or on top of a single cup (the pot). The "subassembly strategy" involves combining two or more cups, which are men placed as a unit (or subassembly) on top of or into one or more cups. The subassembly strategy is considered the most complex because it requires a hierarchical combination of multiple cups. Two or more cups become a subunit, which functions as a single unit in the next movement sequence. Greenfield et al. (1972) noted that in subassembly, role reversal is evident hi that the cup that is acted on becomes the actor in the subsequent movement sequence such that Cup B is first in a passive role (it receives Cup A) and then hi an active role (the nested pair containing Cups A and B are put into Cup C as a unit). In the less complex form of combination, potting, there is no role reversal from passive to active role. In children, these strategies appear in sequential order (Greenfield, 1991; Greenfield, Brazelton, & Childs, 1989; Greenfield et al., 1972). At 11 months of age, the majority of middle-class children in Cambridge, Massachusetts, like Zinacantec Maya children in Chiapus, Mexico, combined the cups by making pairs. By 21 months of age, the pot strategy becomes the dominant combinatorial method. By 36 months of age, the subassembly strategy was evident in both groups of children, although it was not the dominant 137