The sources of skill in seriating cups in children , monkeys and apes

Is a concept of either reversibility or of hierarchical forms of combination necessary for skilled seriation? We examined this question by presenting seriating cups to adult capuchin monkeys and chimpanzees and to 11-, 16and 21-month-old children. Capuchins and chimpanzees consistently created seriated sets with five cups, and placed a sixth cup into a previously seriated set. Children of all three ages created seriated five-cup sets less consistently than the capuchins and chimpanzees, and were rarely able to place a sixth cup into a seriated set. Twenty-one-month-olds produced more structures containing three or more cups than did the younger age groups, and these children also achieved seriated sets more frequently. Within all participant groups, success at seriating five cups was associated with the frequency of combining three or more cups, regardless of form. The ability to integrate multiple elements in persistent combinatorial activity is sufficient for the emergence of seriation in young children, monkeys and apes. Reliance on particular methods of combination and a concept of reversibility are later refinements that can enhance skilled seriation. Young children through the preschool years are typically attracted to sets of objects that present ordered relationships of size or volume, and they will work spontaneously to create structures that make use of, or express, the ordered relationships present in the collection (e.g. Inhelder & Piaget, 1969; Sinclair, Stambak, Lezine, Rayna & Verba, 1989). For example, children are likely to stack blocks from largest to smallest, or to nest cups of different sizes. Children’s efforts to nest cups move from initial limited actions (pairing two objects) through ineffective sequences that result in structures of varying sizes and compositions, to wellordered and effective action sequences that consistently produce seriated sets (Greenfield, Nelson & Saltzmann, 1972; Woodward, 1972). Once the child can seriate a set of cups effectively, that child can subsequently insert additional cups in the correct position in the seriated set. This achievement marks skilled seriation of cups. Skill encompasses both the creation of a seriated set, and the expansion of a seriated set. The development of skill in this simple seriation task poses many interesting questions for developmental scientists. Most investigators looking at activity with nesting cups have approached this task from the perspective of hypothesized cognitive elements embodied in the successive acts of combining cups. For example, Greenfield et al. (1972) found that children who are successful at seriating five cups, and at placing a sixth cup into a seriated set, rely more on a method of combining cups that the authors labeled ‘subassembly’ than they do on the two other possible methods of combining the cups (see Figure 1). The simplest method, and one that can never result in a seriated set if used exclusively, is called ‘pairing’. Pairing involves putting one cup together with one other cup. Subassembly involves placing one cup into another (or a set of others), then moving the multicup unit as one element into a third cup. Along with placing one cup into a set of others (called ‘potting’), subassembly results in the creation of multicup structures. The difference between potting and l ll lis rs t . , 108 Cowley Road, Oxford OX4 1JF, UK and 350 Main Street, Malden, MA 02148, USA. DSC16 2/1/02, 11:51 AM 118 © Blackwell Publishers Ltd. 2002 Seriation in children and nonhuman primates 119 Figure 1 Strategies of combining nesting cups as identified by Greenfield et al. (1972). subassembly is that the former involves a single actor and multiple recipients; the latter involves multiple actors and a single or multiple recipient(s). In Greenfield’s (1991) terminology, subassembly results in the hierarchical combination (two or more lower-level units combined into one new unit) of multiple cups; pairing and potting do not. In cross-sectional sampling, Greenfield et al. (1972) observed a developmental progression with age in the reliance on different patterns of combining cups, from pairing to potting to subassembly, and an increase in success at seriation with the increasing use of subassembly (see also Sugarman, 1983). DeLoache, Sugarman and Brown (1985) also report, in another crosssectional study, that children 18 months to 42 months showed decreasing reliance on potting and increasing use of subassembly. Success at seriation also increased with age, as in Greenfield et al.’s (1972) and Sugarman’s (1983) studies. Greenfield et al. (1972) and Greenfield (1991) argue that subassembly, because it involves hierarchical combination, illustrates a more sophisticated approach to the problem of arranging multiple objects than does potting. Greenfield and colleagues attribute the older children’s increasing success at seriation to increasing reliance on a subassembly strategy for combining the cups. Further, Greenfield et al. (1972) and DeLoache et al. (1985) suggest that the development of skill at seriating cups, and particularly success at placing a middle cup into an existing seriated set, reflects the child’s growing recognition that one cup can simultaneously be larger than a specific other cup, and smaller than a different other cup. In other words, middle cups must be placed in a certain order to fit correctly. The ability to fit the cups together consistently is taken as evidence that the behavior is conceptually mediated; and in this view, that the child recognizes (at the level of action) the property of reversibility in the cups (because such recognition is necessary for success at the task). The word ‘strategy’ to describe recurrent patterns of actions with the cups reflects this conceptual interpretation of the nature of skill in seriation (Greenfield et al., 1972). As initially proposed by Inhelder and Piaget (1969), mastery in performance (skill) in seriation tasks is taken as evidence that the performer uses a concept of reversibility to organize action. Reversibility refers to the premise that what can be done (or composed) can be undone (or decomposed). With respect to logical cognition, this sense of reversibility entails recognition that different whole units can be combined to form a new, inclusive whole, but that this whole can potentially be broken down, or the additive operation reversed, to reinstate the smaller wholes. With respect to seriation, reversibility implies an understanding that a single cup can simultaneously be smaller than one cup and larger than another cup and that its role changes (reverses) depending on which relation is being considered. In this study, we examine seriation in very young children (11 to 21 months-old), when seriation skill is DSC16 2/1/02, 11:51 AM 119 120 Dorothy M. Fragaszy et al. © Blackwell Publishers Ltd. 2002 emerging. Previous studies (Greenfield et al., 1972; DeLoache et al., 1985) have shown that children between 11 and 20 months are not often successful at seriating five cups, and children in this age range who do manage this task usually cannot manage to insert a middle cup into an already-seriated set. Greenfield et al.’s (1972) analyses emphasized age differences in one aspect of action (the children’s reliance on particular patterns of combination, and most especially, subassembly). Sugarman (1983) assessed the organization of activity with nesting cups in terms of ‘local’, or move-by-move, planning. DeLoache et al. (1985) expanded the focus of their study to include how children managed errors committed during pursuit of seriation. The current study extends the previous works by attending particularly to combinatorial activity in very young children, and by broadening the theoretical consideration of the initial bases of seriation skill. Children from 1 to nearly 2 years of age master combinatorial manipulation in many situations (e.g. using a spoon and other simple tools; Connolly & Dalgleish, 1989; Brown, 1990; Johnson-Pynn, 1999) and exhibit spontaneous combinatorial manipulation in playful situations (Fenson, Kagan, Kearsley & Zelazo, 1976; Sinclair et al., 1989; Langer, 1986). Thus we expected to see mastery of some components of seriation within this age range. For example, we anticipated that older children, compared to younger children, would combine the cups in increasingly more complicated relational ways, even if they were not particularly successful at seriation. Case’s (1992; Case & Okamoto, 1996) neo-Piagetian theoretical framework offers a more recent theoretical basis from which to consider the development of seriation skill. Case proposes that (1) cognitive activity deploys central conceptual structures, (2) cognitive development involves transformations of these central conceptual structures and thus (3) cognitive development will proceed in a linked, stage-like fashion at least within broad domains of activity. The recurring element of conceptual transformations driving these changes is the nature of the integration of multiple elements into one unit of action. Simultaneous integration of properties is indicative of a more developed conceptual structure than sequential integration because the two properties are handled as one unit rather than successively. With respect to seriation of cups, Case’s (1992) model suggested to us that children’s initial combinations of cups will involve sequential actions moving one cup into or onto another (Stage 1.2; typically evident at about 8–12 months in humans, according to Case). The next form (Stage 1.3; typically evident from 12–18 months) involves monitoring the structures arising from sequential actions, and integrating the sequential actions into a coherent system. In this stage, the child will work to create a stable structure with two or more cups, disassembling stacks that are not stable and re-combining cups to achieve stability. Pairing and potting (moving single cups) would characterize activity in both of these stages. At about 20 months (Stage 2.1), the child is able to coordinate two relational structures simultaneously. This achievement should permit more efficient sequential actions with cups, and encourage subassembly. The child’s goal at this stage would be to put three or more cups together into a stable structure. Seriation skill could be evident here, although relatively inefficient (where efficiency is measured as the number of moves required to achieve seriation). The next improvement (Stage 2.2; 27– 42 months) would appear as expanded attention to two relational units, such as adding cups to the set and (at the same time) dealing with cups that block seriation. Efficiency at seriation could be expected to improve in this stage compared to Stage 2.1. Preschoolers (Stage 2.3; 3–5 years) should be able to focus attention on one working stack, and coordinate a series of actions with this stack to achieve efficient seriation of all the available cups. Furthermore, inserting a middle cup into an existing seriated set of cups should be manageable for children at this stage. Stage 3 (from 5 years), where ordinal skills can be expected, might be evident as consistently perfect or nearly perfect seriation, via any method of combination. We expected that the 11to 21-month-old children in our study would be operating at Stages 1.3–2.1 in Case’s (1992) scheme: some focusing on a single action at a time (putting one cup together with another), and others working on the relational goal of making a stable structure with multiple cups. We anticipated that children attempting to make multi-cup structures would use all combinatorial methods (pair, potting and subassembly). We were particularly interested in how these children achieved seriation, if they did so, given that either the potting or subassembly method of combining multiple cups is adequate for the purpose. Does the use of subassembly precede seriation, or does attempting to master seriation lead one to use subassembly as an efficient solution to the problem? Our study also includes a comparative element. We compare the performance of young children with that of monkeys and apes in the same seriation task. We have shown in an earlier study (Johnson-Pynn, Fragaszy, Hirsh, Brakke & Greenfield, 1999) that monkeys and apes can seriate nesting cups with skill, even managing the problem of inserting the middle sixth cup with high rates of success. They did so without a strong reliance on subassembly, although all our participants used subassembly at least occasionally to combine the cups, and DSC16 2/1/02, 11:51 AM 120 © Blackwell Publishers Ltd. 2002 Seriation in children and nonhuman primates 121 proportional use of subassembly was positively associated with seriation of five cups. We compare the data from monkeys and apes (taken from Johnson-Pynn et al., 1999) in this report to examine whether young humans’ patterns of action with cups are similar to those seen in other species not known to achieve mature conceptual formulations of seriation (such as reversibility).