LANGUAGE LEARNING IN CHILDHOOD

Transcription

1 How do we learn language? LANGUAGE LEARNING IN CHILDHOOD Language is a species-specific cognitive skill Ability to learn language is only marginally related to general intelligence and does not seem to depend on specific sensory input Kevin A. Shapiro, MD, PhD UCSF Osher Mini Medical School 4 November 2015 How do we learn language? we have two dogs w i ɦ æ v t h ʉ d ɑ g z

2 Elements of language learning Discriminating speech from non-speech Determining the number of languages in the environment Identifying units of language (sounds, words, phrases) Assigning meaning to word units Identifying rules to combine units of language in ways that allow the expression of more complex meanings Maintaining separate sets of units for different languages two две NP dogs собаки wiɦævt h ʉdɑgz arf! unasjest arf! j dv j esabaki Elements of language learning Discriminating speech from non-speech Determining the number of languages in the environment Identifying units of language (sounds, words, phrases) Assigning meaning to word units Identifying rules to combine units of language in ways that allow the expression of more complex meanings Maintaining separate sets of units for different languages Learning correspondences between sounds and symbols We have two dogs Унас естьдвесобаки wiɦævt h ʉdɑgz unasjest j dv j esabaki Key questions Language learning is not really something that the child does; it is something that happens to the child placed in an appropriate environment, much as the child s body grows and matures in a predetermined way when provided with appropriate nutrition and environmental stimulation. How is language acquisition reflected by maturation of the brain language network? What kinds of differences in language learning exist between individuals? Chomsky, 1988, 134

3 The talking brain Parietal lobe The talking brain Motor sequencing Frontal lobe Sound sequencing (Articulatory phonology) Word sequencing (Syntax) Hearing Occipital lobe Spoken word form (Phonology) Word meaning (Semantics) Temporal lobe Vision The reading brain Language connections Motor sequencing Arcuate fasciculus Sound sequencing (Articulatory phonology) Word sequencing (Syntax) Temporal-parietal component of arcuate Hearing Spoken word form (Phonology) Word meaning (Semantics) Visual word form Vision Inferior longitudinal fasciculus

4 Studying the infant brain How does the language network develop? Newborn brain discriminates speech from non-speech Right hemisphere Forward speech Backward speech Silence Courtesy P. Kuhl Peña et al., PNAS 2003;100: How does the language network develop? Left temporal lobe is important for speech detection in newborns How does the language network develop? Left temporal activation for language is diffuse in newborns, becomes more specific over the first year Forward speech Backward speech Silence Right hemisphere Non-language (tones) Language (syllables) Newborns Language (syllables) One year olds Peña et al., PNAS 2003;100: Imada et al., NeuroReport 2006

5 How does the language network develop? Left frontal lobe not sensitive for language in newborns, begins respond to speech around one year of age How does the language network develop? Structural connections develop from temporal (posterior) to frontal (anterior) language areas Non-language (tones) Language (syllables) Newborns Language (syllables) One year olds Dorsal temporal to frontal connections (mature) Dorsal temporal to frontal connections (immature) Ventral occipital to frontal connections Imada et al., NeuroReport 2006 Perani et al., Brain 2011 How does the reading network develop? In inexperienced readers, seeing words activates general visual areas in both left and right hemisphere As reading skill develops, a visual word form area becomes specialized for word recognition The reading brain Motor sequencing Sound sequencing (Articulatory phonology) Word sequencing (Syntax) Hearing Spoken word form (Phonology) Word meaning (Semantics) Schlaggar & McCandliss, Annu. Rev. Neurosci Visual word form Vision

6 Key questions (revisited) How is language acquisition reflected by maturation of the brain language network? What kinds of differences in language learning exist between individuals? About 12% of children have difficulties with spoken language, comprehension, reading, or writing Most common disorder affecting language in childhood is developmental dyslexia (5%) About 15 different genes associated with susceptibility to dyslexia Memory for words Dyslexia genes affect migration of neurons Leads to neuronal abnormalities in the language network? Sound processing Reading disorder Visual processing Rapid word retrieval Attention Ramus, Trends Neurosci. 2004

7 Some individuals with dyslexia show reduced activation in parts of the language network when reading Some differences in brain activation between dyslexics and non-dyslexics change with age 20 Activations within cluster 14 Activations within cluster Reading Other tasks Children Adults Non-Dyslexic Dyslexic Non-Dyslexic Dyslexic Paulesu et al., Front Hum. Neurosci Paulesu et al., Front Hum. Neurosci Activation in visual word form area often not found in dyslexic individuals Richlan et al., 2011, Hum. Brain Mapping; Paulesu et al., Front Hum. Neurosci Summary Language learning requires the ability to recognize and produce novel sounds, words, and phrases Brain networks involved in language learning are usually left hemisphere, maturing in a temporal to frontal pattern Learning to read results in additional brain specialization for recognizing visual word forms Up to 1 in 8 individuals have some difficulty with language, such as developmental dyslexia Dyslexia may be associated with difficulties in several aspects of language Individuals with dyslexia have structural and functional differences in their language networks

8 References Imada et al., Infant speech perception activates Broca s area: a developmental magnetoencephalographic study. NeuroReport 2006;17:956 Kuhl et al., Linguistic experience alters phonetic perception by 6 months of age. Science 1992;255:606 Paulesu et al., Reading the dyslexic brain: multiple dysfunctional routes revealed by a new meta-analysis of PET and fmri activation studies. Front. Hum. Neurosci. 2014;8:830 Peña et al., Sounds and silence: an optical topography study of language recognition at birth. PNAS 2003;100:11702 Perani et al., Neural language networks at birth. Brain 2011;108:16056 Ramus, Neurobiology of dyslexia: a reinterpretation of the data. Trends Neurosci. 2004;27:720 Schlaggar & McCandliss, Development of neural systems for reading. Annu. Rev. Neurosci. 2007;30:475