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Neural and Behavioral Aspects of Early Language Development

Presenter: Laura-Ann Petitto, Ph.D.

What babies need to acquire language: on cortical specificity and cortical plasticity in the emergence of language

What mechanisms underlie the human capacity to acquire language? Traditional answers have assumed that the maturation of the mechanisms for speaking and hearing neurologically determine the time course, structure and content of very early language acquisition. Comparative studies of hearing and deaf babies in my laboratory, however, have revealed that the maturational time course, structure and content of early signed and spoken language acquisition are the same. Using PET/MRI brain scanning techniques, we also found that the brains of deaf adults showed increased blood flow in highly specific tissue while they processed highly specific parts of natural language. Remarkably, some of the tissue involved brain sites that for more than 125 years have been regarded as being exclusive centers for processing sound and sound alone (planum temporale/superior temporal gyrus). Taken together, the evidence suggests that the human brain may possess specialized tissue dedicated to processing specific patterns relevant to aspects of the structure of natural language--a pattern sensitivity that is both distinct from a specific modality such as sound and highly unmodifiable in so far as languages in radically different modalities will be processed in the same loci. At the same time, the expression of this pattern sensitivity appears to be highly modifiable and can recruit multiple pathways (hands or tongue) as a result of the modality of language input. Thus, human language acquisition appears to entail both specialized tissue and tissue that becomes specialized. One intriguing implication here is that language modality, be it spoken or signed, is so plastic that it only becomes neurologically set through neurogenetic processes after birth.


Dr. Petitto is a cognitive neuroscientist at Dartmouth College, where she is Professor and Director of the "Cognitive Neuroscience Laboratory for Language & Child Development" in the Department of Psychological & Brain Sciences, as well as a Professor in the Department of Education; starting in June 2002, she will also serve as Department of Education Chairman (2002-2007). Dr. Petitto is known for her work on the biological bases of language, especially involving early language acquisition. Her research on this topic spans over 29 years, beginning in 1973 with her role on the Columbia University research project called "Project Nim Chimpsky." As the project's primary teacher and research coordinator, Petitto lived with the chimpanzee and attempted to teach him American Sign Language. More recently, she is known for her discoveries concerning how young human children acquire natural language, be it spoken or signed. She discovered that profoundly deaf babies exposed to signed languages from birth babble on their hands, which possesses the same syllable structure and occurs on the same developmental timetable as hearing babies' vocal babbling (Science, 1991), and that sign-exposed hearing babies raised entirely without speech also produce hand babbling that is rhythmically distinct from all other hand movements that all babies make (Nature, 2001). She has also conducted studies of the cerebral organization for signed and spoken languages using modern brain-scanning techniques and recently found powerful evidence that select brain tissue previously assumed unique to processing specific aspects of speech and sound (the superior temporal gyrus) also processes signed languages (PNAS, 2000). Taken together, her research points to the existence of tissue in the human brain that helps human babies learn language. Presently, she is exploring the role of this tissue in early normal language development, atypical language disorders (e.g., dyslexia), and especially in early childhood bilingual language acquisition. Dr. Petitto received her Masters and Doctoral degrees from Harvard University in 1981 and 1984 (respectively) and built a vibrant laboratory in Cognitive Neuroscience at McGill University (Montreal, Quebec) before moving to Dartmouth in fall 2001. She is the recipient of numerous international awards, including the 1998 Guggenheim Award for her contributions to Neuroscience.