Anne Lehtokoski

Bio: Anne Lehtokoski is an academic researcher from University of Helsinki. The author has contributed to research in topics: Mismatch negativity & Speech perception. The author has an hindex of 13, co-authored 17 publications receiving 3036 citations.

Language-specific phoneme representations revealed by electric and magnetic brain responses

Abstract: There is considerable debate about whether the early processing of sounds depends on whether they form part of speech. Proponents of such speech specificity postulate the existence of language-dependent memory traces, which are activated in the processing of speech1–3 but not when equally complex, acoustic non-speech stimuli are processed. Here we report the existence of these traces in the human brain. We presented to Finnish subjects the Finnish phoneme prototype /e/ as the frequent stimulus, and other Finnish phoneme prototypes or a non-prototype (the Estonian prototype /o/) as the infrequent stimulus. We found that the brain's automatic change-detection response, reflected electrically as the mismatch negativity (MMN)4–10, was enhanced when the infrequent, deviant stimulus was a prototype (the Finnish /o/) relative to when it was a non-prototype (the Estonian /o/). These phonemic traces, revealed by MMN, are language-specific, as /o/ caused enhancement of MMN in Estonians. Whole-head magnetic recordings11,12 located the source of this native-language, phoneme-related response enhancement, and thus the language-specific memory traces, in the auditory cortex of the left hemisphere.

Development of language-specific phoneme representations in the infant brain.

Abstract: Studies using behavioral methods, such as head-turning experiments, in which children are conditioned to turn their heads toward the sound source when they detect a change in the sound, have shown that environment has an important effect on how infants perceive language1,2,3,4. Young infants are able to discriminate almost all phonetic contrasts, whereas older infants discriminate better between phonemes that occur in the language that they normally hear, rather than foreign-language phonemes. Here we demonstrate the development of language-specific 'memory traces' in the brains of the same group of infants between six months and one year of age.

Brain responses reveal the learning of foreign language phonemes.

Abstract: Learning to speak a new language requires the formation of recognition patterns for the speech sounds specific to the newly acquired language. The present study demonstrates the dynamic nature of cortical memory representations for phonemes in adults by using the mismatch negativity (MMN) event-related potential. We studied Hungarian and Finnish subjects, dividing the Hungarians into a naive (no knowledge of Finnish) and a fluent (in Finnish) group. We found that the MMN for a contrast between two Finnish phonemes was elicited in the fluent Hungarians but not in the naive Hungarians. This result indicates that the fluent Hungarians developed cortical memory representations for the Finnish phoneme system that enabled them to preattentively categorize phonemes specific to this language.

Invited review The mismatch negativity (MMN) in basic research of central auditory processing: A review

Abstract: In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream. 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Early language acquisition: cracking the speech code

Abstract: Infants learn language with remarkable speed, but how they do it remains a mystery. New data show that infants use computational strategies to detect the statistical and prosodic patterns in language input, and that this leads to the discovery of phonemes and words. Social interaction with another human being affects speech learning in a way that resembles communicative learning in songbirds. The brain's commitment to the statistical and prosodic patterns that are experienced early in life might help to explain the long-standing puzzle of why infants are better language learners than adults. Successful learning by infants, as well as constraints on that learning, are changing theories of language acquisition.

The Brain Basis of Language Processing: From Structure to Function

Abstract: Language processing is a trait of human species. The knowledge about its neurobiological basis has been increased considerably over the past decades. Different brain regions in the left and right hemisphere have been identified to support particular language functions. Networks involving the temporal cortex and the inferior frontal cortex with a clear left lateralization were shown to support syntactic processes, whereas less lateralized temporo-frontal networks subserve semantic processes. These networks have been substantiated both by functional as well as by structural connectivity data. Electrophysiological measures indicate that within these networks syntactic processes of local structure building precede the assignment of grammatical and semantic relations in a sentence. Suprasegmental prosodic information overtly available in the acoustic language input is processed predominantly in a temporo-frontal network in the right hemisphere associated with a clear electrophysiological marker. Studies with patients suffering from lesions in the corpus callosum reveal that the posterior portion of this structure plays a crucial role in the interaction of syntactic and prosodic information during language processing.