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“Origins of communicative disorders ” to Elizabeth Bates, and by a grant from the John D. and Catherine T. MacArthur Foundation. We are grateful to Larry Juarez and Meiti Opie The effects of focal brain injury are investigated in the first stages of language development, during the passage from first words to grammar. Parent report and/or free speech data are reported for 53 infants and preschool children between 10- 44 months of age. All children had suffered a single, unilateral brain injury to the left or right hemisphere, incurred before six months of age (usually in the pre- or perinatal period). This is the period in which we should expect to see maximal plasticity, but it is also the period in which the initial specializations of particular cortical regions ought to be most evident. In direct contradiction of hypotheses based on the adult aphasia literature, results from 10- 17 months suggest that children with righthemisphere injuries are at greater risk for delays in word comprehension, and in the gestures that normally precede and accompany language onset. Although there were no differences between left- vs. right-hemisphere injury per se on expressive language, children whose lesions include the left temporal lobe did show significantly greater delays in expressive vocabulary and

The term “aphasia ” refers to acute or chronic impairment of language, an acquired condition that is most often associated with damage to the left side of the brain, usually due to trauma or stroke. We have known about the link between left-hemisphere damage and language loss for more than a century (Goodglass, 1993). For almost as long, we have also known that the lesion/symptom correlations observed in adults do not appear to hold for very young children (Basser, 1962; Lenneberg, 1967). In fact, in the absence of other complications, infants with congenital damage to one side of the brain (left or right) usually go on to acquire language abilities that are well within the normal range (Eisele & Aram, 1995; Feldman, Holland, & Janosky, 1992; Vargha-Khadem, Isaacs, & Muter,

Savage-Rumbaugh and her colleagues have provided us with yet another ground-breaking investigation into the linguistic abilities (or "quasi-linguistic abilities " — see below) of our nearest phylogenetic neighbor, the chimpanzee. Their monograph begins with some brief but useful reviews of the primate language literature, and the literature on early comprehension and production of language in human children. The authors document the peculiar bias toward production and the relative neglect of comprehension that have characterized the child language literature, and they ask a perfectly reasonable question: If we want to understand what an organism knows about language, isn't comprehension a better place to start? And if we want to compare knowledge of language in two related species, how can we draw any firm conclusions if our work is based exclusively on what the animal can produce?

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The papers in this issue present a series of comparative studies of language processing and language development across clinical populations, including studies in the earliest stages of language development, as well as aspects of grammar, narrative, and verbal memory across the elementary school years. The populations covered include ‘‘late talkers,’ ’ children with congenital injuries to either the left or right hemisphere, children with Williams Syndrome, children with Down Syndrome, children with a diagnosis of specific language impairment (behaviorally defined), and a range of typically developing controls for each of these groups. As Holland points out in her commentary, two of the most surprising findings across these studies include the following. (1) Despite differences in rate of development, the sequences and error types observed are (with a few interesting exceptions) remarkably similar across these very different clinical groups. It appears that sequences and error types are determined primarily by the ‘‘problem space’ ’ posed by a particular language (in this case English), so that virtually all children who enter into this problem space end up behaving in much the same way, albeit at variable rates. Reilly et al. (this issue) suggest a metaphor for results like these: all of these children have undertaken a journey along the same highway, but some of them are in the slow lane, with occasional stops along the road. (2) Children with well-defined brain injuries of the kind that often lead to aphasia in adults perform within the normal range on most measures once they move into the elementary school years, with no trace of a selective disadvantage for children with left-hemisphere damage

depiction of how an avalanche encodes serial order.