The role of verbal labels in attention to dimensional similarity

The role of verbal labels in attention to dimensional similarity Lynn K. Perry (lkperry@wisc.edu) Department of Psychology, 1202 W. Johnson Street Madison, WI 53706 USA Larissa K. Samuelson (larissa-samuelson@uiowa.edu) Department of Psychology, E11 Seashore Hall Iowa City, IA, 52242 USA Abstract participant were using holistic similarity, she would classify A and C together. If a participant were using dimensional similarity, she would classify A and B together. Smith and Kemler (1977) found that 5-6 year-olds made mostly AC matches and 10-11 year-olds made mostly AB matches. In general, young children focus on holistic similarity and older children focus on dimensional similarity (selectively attending to one property, such as brightness, to the exclusion of others, such as size). Research on early word learning, however, suggests the process of learning words trains attention to category-relevant dimensions. We ask: does word learning scaffold dimensional attention more generally? By showing labels support dimensional attention, these results clarify the processes involved in similarity perception and unify our understanding of attentional processes in word learning with those in a broader context. Keywords: Labels; categorization; selective attention. Over the course of development, we become increasingly skilled at attending to one thing to the exclusion of others (see Hanania & Smith, 2010 for review). For example, adults can easily focus on the color of a lime, rather than its exact shape or size, in order to distinguish it from a lemon. Evidence that older children and adults are generally much better than younger children at selectively attending to one dimension to the exclusion of others comes from a variety of domains, but we still do not know the process by which such changes occur. The goal of this paper is to explore the processes driving changes in selective attention with respect to their effects on similarity perception. Of particular relevance to the current study is the holistic-to-dimensional shift, or the tendency for young children to focus on holistic similarity and older children and adults to focus on dimensional similarity relationships (Smith & Kemler, 1977). Imagine you are presented with an orange, a yellowish-orange ball, and a yellowish-orange toy car. If you are an adult, you would be more likely to group the ball with the car because they match exactly along one dimension (i.e. identical in color). A young child, however, would group the orange with the ball because they are similar along multiple dimensions (i.e. shape and color)— they are holistically similar. This shift in similarity perception occurs during the early school-age years, such that younger children (<8-years-old) tend to be holistic classifiers and older children dimensional classifiers. Free classification, such as the triad classification task pictured in Figure 1, is the standard task used to examine this shift. As can be seen, two stimuli (A and B) match on one dimension (e.g. size) but vary greatly along another dimension (e.g. brightness). The third stimulus, C, is highly similar to A along both dimensions, but not identical to it on either. If a Figure 1: Schematic representation of stimuli used in Smith and Kemler’s 1977 triad classification task. One explanation for this change comes from what we know about the role of word learning in the development of dimensional attention and categorization. For example, Landau & Shipley (2001) demonstrated that when two objects are given the same label, participants generalize it to all intermediate morphs between the objects. If the two objects are given different names, participants divide the intermediates into two distinct categories. Lupyan and colleagues (2007) demonstrated that labels facilitated adults’ category learning. Importantly, in this example, the labels were task irrelevant, providing information redundant with category structure. Other researchers have argued that redundant associations between cues strengthen the associations between other perceptual cues and category structure and that the facilitative effect of labels is fundamentally developmental (Yoshida & Smith, 2005). By this view, over the course of word learning, the frequent redundancy between labels and other cues such as solidity, syntax, and category organization helps children use labels to facilitate learning. The more experience children have learning regularities in these overlapping cues, the better they can attend to relevant dimensions of similarity, at least in the context of further word learning. This is most clearly seen in the development of word- learning biases. For example, children acquire a shape bias, or the tendency to generalize names of novel objects by similarity in shape (Landau et al., 1988). This bias emerges from regularities present in the linguistic environment: a majority of the early words children learn name categories of solid objects organized by similarity in shape, e.g., ball.