Abstract
Speech perception requires rapid extraction of the linguistic content from the acoustic signal. The ability to efficiently process rapid changes in auditory information is important for decoding speech and thereby crucial during language acquisition. Investigating functional networks of speech perception in infancy might elucidate neuronal ensembles supporting perceptual abilities that gate language acquisition. Interhemispheric specializations for language have been demonstrated in infants. How these asymmetries are shaped by basic temporal acoustic properties is under debate. We recently provided evidence that newborns process non-linguistic sounds sharing temporal features with language in a differential and lateralized fashion. The present study used the same material while measuring brain responses of 6 and 3 month old infants using simultaneous recordings of electroencephalography (EEG) and near-infrared spectroscopy (NIRS). NIRS reveals that the lateralization observed in newborns remains constant over the first months of life. While fast acoustic modulations elicit bilateral neuronal activations, slow modulations lead to right-lateralized responses. Additionally, auditory-evoked potentials and oscillatory EEG responses show differential responses for fast and slow modulations indicating a sensitivity for temporal acoustic variations. Oscillatory responses reveal an effect of development, that is, 6 but not 3 month old infants show stronger theta-band desynchronization for slowly modulated sounds. Whether this developmental effect is due to increasing fine-grained perception for spectrotemporal sounds in general remains speculative. Our findings support the notion that a more general specialization for acoustic properties can be considered the basis for lateralization of speech perception. The results show that concurrent assessment of vascular based imaging and electrophysiological responses have great potential in the research on language acquisition.
Highlights
The analysis of acoustic features in the continuous auditory speech stream is a prerequisite for language acquisition in infancy
Our findings support the notion that a more general specialization for acoustic properties can be considered the basis for lateralization of speech perception.The results show that concurrent assessment of vascular based imaging and electrophysiological responses have great potential in the research on language acquisition
Near-infrared spectroscopy The general linear model (GLM) based on the oxygenation changes yielded β-values of changes in oxy- and deoxy-Hb for fast (12 and 25 ms) and slow (160 and 300 ms) acoustic modulations
Summary
The analysis of acoustic features in the continuous auditory speech stream is a prerequisite for language acquisition in infancy. Among other functions it serves the segmentation of the speech stream into smaller units, like words and phrases (Mehler et al, 2004; Gervain and Mehler, 2010). This very early step of speech perception necessitates temporal and spectral differentiation of the acoustic input. Taken together there is converging evidence that basic aspects of lateralization in the network in response to complex auditory www.frontiersin.org
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