Word learning biases are certain biases or assumptions that allow children to quickly rule out unlikely alternatives in order to effectively process and learn word meanings. They begin to manifest themselves around 18 months, when children begin to rapidly expand their vocabulary. These biases are important for children with limited processing abilities if they are to be successful in word learning. The guiding lexical principles have been defined as implicit and explicit strategies towards language acquisition. When a child learns a new word they must decide whether the word refers to the whole object, part of the object, or the object's characteristics, solving an indeterminacy problem.
Whole object assumption One way in which children constrain the meaning of novel words is through the whole object assumption. When an adult points to an object and says a word, a child assumes this word labels the entire object, not parts or characteristics of the object. For example, if a child is shown an object and given the label "truck", the child will assume "truck" refers to the entire object instead of the tires, doors, color or other parts. Ellen Markman pioneered work in this field. Her studies suggest that even in cases where color or a dynamic activity is made salient to children, they will still interpret the new word as a label for whole objects. According to cognitive psychologist Elizabeth Spelke, infants' perception of the physical world is guided by three constraints on the behavior of physical objects: objects must move as wholes, objects move independently of each other, and objects move on connected paths. These three constraints help guide children's interpretations of scenes, and, in turn, explains how the whole object bias reflects the non-linguistic status of objects.
Domain specificity It is unclear if the word-learning constraints are specific to the domain of language, or if they apply to other cognitive domains. Evidence suggests that the whole object assumption is a result of an object's tangibility; children assume a label refers to a whole object because the object is more salient than its properties or functions. The whole object assumption may reflect non-linguistic levels of an object and exploits the cognitive tendency to analyze the world through a whole object lens, meaning the whole object assumption can be applied to cognitive domains outside of language.
Criticisms One criticism of the whole object assumption is that much of the evidence provided is only for children 18 months and older. A more recent study strengthened the breadth of ages and stimuli conditions under which this bias occurs. As early as 12 months, infants can associate words with whole objects when the objects can be viewed as two separate objects and even when one of the parts is made salient. Another criticism is the claim that a limited set of stimuli has been used that possibly favors a "whole" interpretation. To address this criticism, the whole object assumption has also been tested with adults. Even when participants between the ages of 18–36 were instructed that they would be tested more frequently for parts, they were better able to recognize the whole objects rather than parts. These findings support the hypothesis that there is a tendency to encode the overall shape of the stimuli in working memory, rather than individual details.
Taxonomic assumption After a child constrains a novel word to label a whole object, the child must learn how to apply the label to similar objects. Ordinarily, children focus on thematic relations between objects when categorizing. For example, if given soup, children will group it together with a bowl and a spoon. Those items would be thematically related. However, when children are given a new label they shift their attention to taxonomic relationships. What this means for the previous example is instead of soup being related to a bowl or spoon, children relate it to ice cream or pudding. The new label is assumed to refer to other objects within the same taxonomic category. The exact nature of taxonomic assumption is unclear. Baldwin finds that shape is the primary influence of children's expectations towards novel objects. Children draw from a wide variety of characteristics to make inferences, although shape is typically the most prevalent. Ellen Markman's early studies showed this constraint at work. When two- and three-year-olds were presented with two basic-level objects, two different kinds of dogs, and a third thematically related object, dog food, they showed a tendency to select a dog and dog food; however, if one of the dogs was labeled with an unfamiliar word, the children were more likely to select the two dogs. Another study conducted by Backscheider & Markman attempted to clarify whether this assumption was powerful enough to overcome the preference for thematic relations when objects are engaged in dynamic thematic relations at the time of labeling. A doll was repeatedly seated in a chair when the child either heard "see the bif" or "see this". The label, "bif", caused children to pick objects of the same kind, whereas, the absence of the label caused them to organize objects to the thematic event they had witnessed. Children use this assumption as early as 18 months of age. Similar to the taxonomic constraint researchers have looked into the principle of categorical scope, which also follows the assumption that children will believe new object labels refer to objects within taxonomic categories. An example of categorical scope and perceptual similarity can be illustrated when children learn animal names. Studies show that children think the identity of an animal only changes if its internal properties change. Children extended labels to two perceptually similar animals more often than when they were dissimilar.
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