General and specific word knowledge as predictors of children's categorization

There is a debate in the literature as to whether young children’s categorization abilities are more closely related to their general productive vocabulary or their specific word knowledge. The present study examines this relationship in children 18 to 26 months of age. Specifically, it tests the hypothesis that children’s understanding of individual words is more closely related to their category performance than the overall size of their productive vocabulary. Twenty children at 19 months (range= 18-20 months) and 25 months of age (range= 24-26 months) participated in the study. Children’s category performance was assessed using an object manipulation task with novel objects. Half of the children received novel names for the novel objects, and half did not. Two measures were then assessed: children’s knowledge of the novel names in a comprehension test, and children’s productive vocabulary outside of the laboratory, as measured by a parental checklist. Consistent with previous findings, the results indicate that children with larger productive vocabularies show more advanced categorizing. More importantly, however, the data suggest that children who received names for the novel objects outperformed children who did not receive the names, regardless of the size of their productive vocabulary. These findings suggest that hearing object names help children categorize objects, and may be a better predictor of children’s category performance than their productive vocabulary. General and Specific 3 General and Specific Word Knowledge as Predictors of Children’s Categorization Children experience rapid advances in their cognitive and linguistic abilities toward the end of their second year. One important cognitive skill that appears during this time is their ability to categorize objects. Researchers have observed that when young children are presented with two distinct categories of objects in an object manipulation task, they may exhibit spontaneous sorting behavior in which they sequentially touch, and sometimes spatially group, first one and then the other set of objects (e.g. Riccuiti, 1965; Starkey, 1981; Sugarman, 1981). This dual sorting behavior, involving both classes of objects, indicates that children are able to recognize the similarities and differences between category members (Riccuiti, 1965; Sugarman, 1981). According to Sugarman (1981), this advanced sorting behavior indicates that children are able to “extend a class to a set of discrete elements. ” Researchers suggest that this implies representational thought. That is, children are able to conceptualize that several things that exist are from the same category and are the same “kind” of thing (Riccuiti, 1965; Sugarman, 1981). Numerous researchers have used an object manipulation task to study age related changes in category development. Categorization performance is found to increase with age. For example, Starkey (1981) examined children’s categorization abilities at six, nine, and 12 months of age. He found that categorization behaviors were absent at six months of age, however by 12 months of age, children reliably sequentially touched three or four objects from one category. Also, he found that dual category behavior, in which children spatially group two categories of objects separately or sequentially touch both categories of objects, had not yet appeared at 12 months of age. Based on these results, Starkey suggested that selective manipulation of one class of objects emerged somewhere between General and Specific 4 nine and 12 months of age. Using the same task, Sugarman (1981) documented an increase in children’s abilities to dual categorize two classes of objects from 18 to 36 months. She found that by 36 months, children were reliably able to selectively touch or group both sets of objects. Additionally, Riccuiti (1965) found a sharp increase in advanced category behavior at 18 months of age, which he explained as possibly an effect of sampling variation or a methodological flaw. More recently, however, other researchers have documented a similar increase around this age (e.g. Gopnik & Meltzoff, 1987; Poulin-Dubois, Graham, & Sippola, 1995). Current research has focused on the relationship between cognitive development and concurrent increases in categorization abilities. One important milestone that usually occurs around 18 months of age is a period of accelerated vocabulary growth, known as the vocabulary spurt. During this time, children add new words to their productive vocabularies at an accelerated rate (Benedict, 1979). The vocabulary spurt is not an entirely universal phenomenon, but for most children it usually occurs between 18 to 20 months of age, or after they have over 50 words in their productive vocabularies (Gershkoff-Stowe & Smith, 1997; Goldfield & Reznick, 1990). Several researchers have investigated the developmental relationship between this linguistic advancement and concurrent developments in categorization. For example, Gopnik and Meltzoff (1987) reported a close temporal association between the development of advanced categorization skills and the onset of the vocabulary spurt. All of the children in their study demonstrated advanced category behavior before or at the same time as the onset of the vocabulary spurt, suggesting that children need to have achieved certain cognitive milestones in order to experience a vocabulary spurt. Further, General and Specific 5 they suggested that infants reflect the knowledge that objects belong in categories by naming and grouping objects. Poulin-Dubois, Graham, and Sippola (1995) also found that children experienced a significant improvement in categorization skills at the onset of the vocabulary spurt. Their findings additionally support Gopnik and Meltzoff’s (1987) claim that the advancement of these cognitive abilities is temporally related to the onset of the naming explosion. However, if these claims hold true, what are the implications for children who fail to demonstrate a rapid increase in their productive vocabulary? In Goldfield and Reznick’s (1990) longitudinal study, five out of 18 children did not demonstrate a vocabulary spurt. Were those five children unable to achieve advanced categorization skills? Research by Gershkoff-Stowe, Thal, Smith, and Namy (1997) suggests otherwise. They failed to replicate Gopnik and Meltzoff’s (1987) finding that the onset of the vocabulary spurt was strongly related to the emergence of advanced categorization skills. Instead, they suggested that increased categorization abilities should be more closely related to children’s word comprehension rather than production. They reasoned that if, as Gopnik and Meltzoff (1987) suggested, children reflect their understanding of categories by word production, then it follows that this knowledge would be first reflected in word comprehension which typically precedes production (Ingram, 1974). In support of this idea, Gershkoff-Stowe et al. (1997) additionally compared children who were “latetalkers,” with a small productive vocabulary, to children who were matched in age and also children who were matched in productive vocabularies. They found that the late-talkers reliably outperformed the vocabulary-matched children in a categorization task, but did not perform reliably differently than the age-matched children. This finding further supports General and Specific 6 the idea that comprehension, rather than production, is more closely associated with the emergence of advanced categorization behavior. Riccuiti, Thomas, and Riccuiti (1999) added further support to the claim that children’s comprehension of words is closely related to their categorization abilities. In their study, children were presented with an object manipulation task in which they were encouraged to sort common objects for which they had names (e.g. cup, shoe). They found that children’s advanced category behavior in this task was highly correlated with their knowledge of the labels for the common objects. Additionally, Waxman and Markow (1995) found that giving infants novel names for objects helped them categorize these objects. They suggested that labels may help infants form categories of objects, as giving several different objects the same label implies that they are the same “kind” of thing. Taken together, the literature presents contradictory evidence concerning what factors are related to changes in children’s categorization abilities. Is the emergence of advanced categorization abilities more closely related to children’s productive vocabulary, as Gopnik and Meltzoff (1987) and Poulin-Dubois et al. (1995) suggested? Or, is comprehension a better predictor of children’s categorization skills, as Gershkoff-Stowe et al. (1997) suggested? A related question, based on Riccuiti and colleagues’ (1999) findings, is how specific word knowledge is related to children’s ability to categorize. The purpose of the current study is to address these questions exploring whether understanding and labeling novel objects facilitates children’s ability to categorize those objects at different stages of productive vocabulary growth. Specifically, the present study compares the categorization skills of children during and after the vocabulary spurt using a standard object manipulation task (Riccuiti, 1965; General and Specific 7 Sugarman, 1981). In order to locate children who were either experiencing the vocabulary spurt, or who had already passed through this linguistic milestone, children from two age groups were initially recruited: 18-20 months, and 24-26 months of age. These age groups were selected on the basis on Goldfield and Reznick’s (1990) findings that most children experience the vocabulary spurt between 18-20 months, and further experience a decline in the rate of vocabulary growth at 24 months when children begin to put words together in sentences. Because age is not always an accurate predictor of vocabulary, once re