than intermittent signals, and white noise. Vocalizations mothers use to comfort an infant are typically continuous, low in pitch, and even provide white noise with "shhhh." Coordination is expected, then, between caregivers and offspring, between males and females in courtship rituals, between adults as providers of information and children as recipients of the information. Fernald (in press-b) presented a very thoughtful analysis of this problem in considering an evolutionary perspective in human maternal vocalizations, documenting the parallels between adult speech to human infants and what is known about the evolution of vocal communication systems in other species.
In the case of word learning, some degree of coordination between parental input to children and word-learning biases would be expected. Finding, for example, that parents tend to label objects for children does not in itself weaken the claim that children are predisposed to consider objects as the referents of novel labels. Such coordination between learning mechanisms and input is likely. Redundancy poses an experimental problem, however, in that alternative explanations for the same phenomena become possible. Experimental rigor requires that to document a given word-learning bias guides children's hypotheses one must rule out alternative explanations (including input) as possible contributing factors in a given experiment. But this should not be confused with a claim that in naturally occurring word learning these factors are irrelevant or should systematically conflict with the postulated word-learning assumptions. On the contrary, redundancy and coordination of word-learning biases and other sources of information should be common. Acquiring vocabulary is essential for language learning and any abilities children have to infer the communicative intent of the speaker, to retain information about past uses of words, to analyze the social situation in which a word is used will be exploited along with word-learning constraints to solve this problem.
I thank Mark Lepper, Michael Maratsos, and Robert Siegler for their discussions of some of these issues and John Flavell, Paul Rozin, and Amanda Woodward for their helpful comments on this manuscript. This work was supported in part by NIH grant HD 20382 and by NFS grant BNS-9109236.