Exploring the Developmental Feedback Loop: Word Learning in Neural Networks and Toddlers

Exploring the Developmental Feedback Loop: Word Learning in Neural Networks and Toddlers Clare E. Sims (Clare.Holtpatrick@Colorado.Edu) Department of Psychology & Neuroscience, 345 UCB Boulder, CO 80309-0345 USA Savannah M. Schilling (Savannah.Schilling@ Colorado.Edu) Department of Electrical, Computer & Energy Engineering, 425 UCB Boulder, CO 80309-0425 USA Eliana Colunga (Eliana.Colunga@Colorado.Edu) Department of Psychology & Neuroscience, 345 UCB Boulder, CO 80309-0345 USA Abstract Children’s Early Vocabularies Early word learning may be supported by a developmental feedback loop: the kind of words a child learns early on support the development of attentional biases, which in turn facilitate further word learning. In neural network simulations and a longitudinal study of toddlers we investigated how the emergence of an attentional bias to shape in word learning impacts vocabulary growth with respect to different kinds of words. If this relationship is causal, we should see that the emergence of a shape bias leads to an increase in the rate of learning of shape-based words relative to other kinds of words. The networks supported this prediction, showing an acceleration of shape- compared to material-based word learning. However, in toddlers, shape- and material-based words were learned similarly around the shape bias emergence. Implications are discussed for the developmental feedback loop account and causal relationships between attentional bias development and vocabulary growth. Keywords: Word learning; shape bias; neural networks; longitudinal study. Introduction Children are skilled word learners, in part because of constraints on the range of things they consider when inferring the referent of a new word. These constraints, sometimes referred to as biases, operate by helping children direct attention, resulting in sensitivity to what information matters most in the context of learning different kinds of words. Although there is debate on the origin of these attentional biases (e.g., Samuelson & Bloom, 2008), evidence from children and from networks suggest that children can learn biases based on the kinds of nouns they acquire early on in their vocabularies (e.g., Colunga & Smith, 2005; Gerhshkoff-Stowe & Smith, 2004). This account entails a developmental feedback loop: the early nouns that children learn give rise to attentional biases, and those biases in turn guide further word learning and impact the structure of children’s growing vocabularies. In the current paper we use data from neural networks and toddlers to investigate the latter part of this loop, focusing on how different types of words are learned right around the pivotal moment of word learning bias development. Words are an important building block in language and cognitive development. Children make the process of word learning look deceptively simple, typically acquiring their first word around the age of 1 year and experiencing a spike in vocabulary development around 18 months of age (Goldfield & Reznick, 1990). Some researchers have observed that this vocabulary spike does not tend to occur until a child has at least 50 words in his or her vocabulary (Lucariello, 1987). Other work shows that the vocabulary spike is not only a function of the number of words a child knows, but also depends on the kinds of words that children learn. For example, Goldfield and Reznick (1990) observed that children exhibiting a vocabulary spike tended to add many words for objects (i.e., nouns) to their vocabularies. Children who did not show this dramatic increase in vocabulary size were steadily adding various types of words instead. This result suggests that while vocabulary size may be one key factor in children’s language development, the specific kinds of words that children learn also play a role. More recent research has investigated the question of why learning nouns may help accelerate subsequent vocabulary growth. One reason is that many different nouns have a basic property in common: they tend to refer to categories of things that are alike in shape. For example, a child will hear the word “ball” used to label a variety of spherical objects. Over time, children may pick up on the general pattern that shape is an important feature when talking about things in the world, and this insight in turn facilitates further word learning. Support for this account comes from a longitudinal study of young children’s vocabularies (Gershkoff-Stowe and Smith, 2004). Over a three month period, 17-month-old children had a greater increase in object label nouns compared to other types of words. Over this same time period, children attended more to shape, over and above other features, when generalizing a newly learned word to novel objects. This result suggests that as children learn certain kinds of words, they also learn reliable patterns or constraints about how those words are used in the world. In