95

When they learn a new word, young children need to understand which are the relevant dimensions. The relevant dimensions are not always very salient, whereas salient properties might be conceptually irrelevant. This review illustrates the benefits of comparing simultaneously two (or more) examples introduced as members of the same category. This situation has been shown to be more effective for understanding the relevant dimensions than the presentation of a single example or of several items introduced sequentially. We present studies showing that situations in which training examples are given are more effective than situations in which the examples are not labeled. We also include comparisons of nouns for objects and nouns for relations (e.g., neighbor, addition). We comment upon the costs of comparison associated with the number of examples, for young children. As a conclusion, simple mechanisms of comparison are presented, including alignment.