The primary questions of the present study were whether there was a significant indirect effect of shyness on vocabulary through executive functioning and whether home environmental stimulation moderated the mediated link between shyness and vocabulary. Consistent with our expectations, executive functioning mediated the shyness-vocabulary link, and the mediation was stronger at high levels of environmental stimulation. Examination of alternative hypotheses in which shyness was examined as a moderator or mediator of the relation between executive functioning and vocabulary found no evidence for these relationships.
That shyness was indirectly linked with poorer vocabulary scores is consistent with some previous research (e.g., Gewirtz, 1948
; Spere et al., 2004
), suggesting that shyness may be negatively associated with vocabulary acquisition. The finding of a positive relation between executive functioning and vocabulary also supports previous research (e.g., Gathercole et al., 1992
; McClelland et al., 2007
), adding more evidence to the notion that cognitive control is necessary in the acquisition of vocabulary. These findings call attention to the importance of executive functioning skills in development and the need for further research that addresses the link between shyness and executive functioning.
The significance of the indirect link between shyness and vocabulary through executive functioning suggests that shyness may be associated with the distribution of attention toward word-learning events through the relation with executive functioning skills. This in turn may be associated with the acquisition of vocabulary. These effects, however, were more pronounced in stimulating home environments; children with better executive functioning skills develop stronger vocabularies when reared in stimulating environments than when reared in less stimulating environments. The negative arousal of shy children in social situations may interfere with their ability to exert the cognitive control necessary to learn new words, particularly in stimulating environments.
Results of this research indicated a significant interaction between executive functioning and environmental stimulation in the prediction of vocabulary. This result implies that children with higher executive functioning skills who are reared in more environmentally stimulating homes may be more likely to develop large vocabularies compared to children with higher executive functioning skills who are reared in less stimulating environments; children with stronger executive functioning skills who are reared in stimulating environments might have an added bonus and therefore develop better vocabularies than their counterparts with who are reared in less stimulating environments.
Home environmental stimulation is important for all children, regardless of their temperamental characteristics. However, our results indicate that not all children may benefit fully from the environmental stimulation parents provide. First, results indicated that children in more stimulating environments with weaker executive functioning skills may perform no better than their counterparts who are reared in less stimulating environments. Thus, home environmental stimulation may not by itself promote the development of vocabulary in all children. Additionally, the negative association between shyness and executive functioning skills we observed suggests that shy children may benefit less than other children from their stimulating environments with regard to vocabulary development to the extent that shyness may interfere with the effectiveness of executive functioning skills.
The results of the present study have important applications for intervention and treatment efforts for children and for making educators and caregivers aware of the challenges that children may face in the development of vocabulary skills. Most early intervention programs target “at-risk” children-- children who are often reared in families of low socioeconomic status. The effect of home environmental stimulation on child outcomes in the present study was significant over and above income differences, highlighting the importance of home environmental stimulation in child outcomes. However, the findings of this research suggest that it is the combination of a stimulating environment along with child characteristics that produce the strongest outcomes in vocabulary acquisition.
While results of this research highlight the importance of the development and/or maintenance of intervention methods and programs that are aimed at improving the environmental stimulation received by children in their homes, such interventions may not be beneficial for all children. Moreover, the findings of this research underscore the importance of executive functioning skills in development. Based on findings that executive functioning is positively related to vocabulary, it is possible that interventions and treatments for improving the outcomes of children, perhaps especially shy children, could be targeted at improving executive functioning skills, particularly in the early years. There is research suggesting that executive functioning skills can be enhanced through training and schooling (Diamond, Barnett, Thomas, & Munro, 2007
; McCrea, Muller, & Parrila, 1999
), suggesting that incorporating such training procedures into treatment protocols for children might prove fruitful in terms of vocabulary development.
There are several limitations of the present research that should be noted. Foremost, the data were collected at only one time point. Although there is evidence to support the hypothesized direction of effects, we acknowledge that the relations among the variables examined in this research may operate in a manner other than that specified by our model. For example, it has been suggested that some forms of shyness may appear early in infancy, while other forms may appear around the age of four or five, after the emergence of a “sense of self” (Cheek, 1998
; Crozier, 2002
). Therefore, it could be that executive functioning skills, vocabulary, and shyness have reciprocal relationships. However, alternative hypotheses, such as the possibility that shyness mediates the link between executive functioning and vocabulary, and the hypothesis that shyness moderates the link between executive functioning and vocabulary, were tested and were not supported by these data. Nevertheless, that the present research design was non-experimental, such that random selection and random assignment were not employed, restricts our ability to determine the temporal order of effects. Therefore, statements about causality should be interpreted cautiously.
An additional limitation was that only receptive vocabulary was examined. Although productive and receptive vocabulary abilities are related, research has more consistently found a negative relation between shyness and productive vocabulary than between shyness and receptive vocabulary (Coplan & Armer, 2005
). We speculate that results using productive vocabulary measures would be similar to those obtained in this study. However, further research is needed to examine the extent to which this is the case.
It is also possible that shy children do not display their knowledge of vocabulary or executive functioning in unfamiliar research settings. To the extent that shyness is provoked by the novelty of the experimental setting, children’s responses may be inhibited. We believe this possible limitation was minimized in the present study for several reasons. First, as previously mentioned, our measure of vocabulary was receptive rather than productive, and shy children are likely to perform better on tests of receptive vocabulary than tests of productive vocabulary (Crozier & Hostettler, 2003
). Furthermore, the vocabulary and executive functioning tests were administered 30–60 minutes into the laboratory session, giving the children time to become comfortable with the situation and build rapport with the experimenter, and, the lab protocol included activities that aided in the maintenance of rapport throughout the visit. Nevertheless, research suggests that shyness may impede rapport building efforts (Rotenberg et al., 2003
). Therefore, further research should be conducted under conditions that may be more familiar to shy children to see if results replicate. However, in young children of pre-reading age, the source of vocabulary development is primarily through audition and interaction with others. Therefore, even if child performance were restricted due to shyness rather than actual capabilities, this does not run counter to our conjecture that executive functioning skills may decrease with increasing levels of shyness, which is in turn may be implicated in the development of vocabulary, but in fact, may provide increased support for this hypothesis. Similarly, the novelty associated with laboratory settings are in some ways similar to school settings in the sense that school settings can also be very novel and socially intimidating to shy children. Thus, the examination of shyness in the laboratory perhaps represents a more ecologically valid assessment of the kind of problems that will eventually emerge in the school setting than would examination of shyness in more familiar settings3
In addition to the limitations of the research, there are also several strengths, one of them being the diversity of the sample. Research on the relation between and among shyness, vocabulary, and executive functioning have often been conducted using samples of primarily Caucasian children from middle-class homes. The present study includes a more diverse sample of children. Relatedly, the sample size employed in the present research was relatively larger than has often been used in investigations of the link between shyness and vocabulary (e.g., Coplan & Armer, 2005
; Dixon & Smith, 2000
); shyness and executive functioning (e.g., Lieberman, 2000
; Ludwig & Lazarus, 1983
); and executive functioning and vocabulary (e.g., Adams & Gathercole, 1995
; Blair & Razza, 2007
). An additional strength of the research was in its focus on processes by which shyness may come to be related to vocabulary. The results of this study extend previous work in two ways. First, it provides evidence regarding the potential role of executive functioning in the relation between shyness and vocabulary acquisition, thereby adding to our understanding of the role of temperamental characteristics in the development of cognitive abilities. Second, it provides evidence that environmental stimulation moderates the mediation of executive functioning in the association between shyness and vocabulary. These results add to our knowledge of the ways in which temperamental characteristics, such as shyness, may influence vocabulary acquisition.
Future research is needed that not only examines different aspects of shyness and different types of vocabulary as well as other aspects of knowledge, but employs a longitudinal design, to increase understanding of the nature of the relation between shyness and cognitive development as well as the role that environmental stimulation might play in this relation. Results of such research would enhance our understanding of the contexts under which shyness may or may not interfere with cognitive and language development. Finally, while shyness in the U.S. has often been pathologized, there is evidence that shyness is not viewed as maladaptive in some nonwestern cultures such as China (e.g., Chen, Rubin, & Sun, 1992
). Therefore, it would be of interest to examine the extent to which results obtained in the present study would generalize to societies in which shyness is viewed as a valued characteristic of children.
The present study contributes to the extant literature by examining processes that may account for the link between shyness and vocabulary, which very few research studies have done, thereby adding to the theories on the relation between shyness and vocabulary. This research adds to the existing literature by not only examining the potential mediation of executive functioning in the relation between shyness and vocabulary, but also examining environmental stimulation as a moderator of this mediation. The results of this research provide an impetus for further research on the mechanisms by which shyness is related to vocabulary.