Abstract
While children are able to name letters fairly quickly, the automatisation of letter-speech sound mappings continues over the first years of reading development. In the current longitudinal fMRI study, we explored developmental changes in cortical responses to letters and speech sounds across 3 yearly measurements in a sample of 18 8–11 year old children. We employed a text-based recalibration paradigm in which combined exposure to text and ambiguous speech sounds shifts participants’ later perception of the ambiguous sounds towards the text. Our results showed that activity of the left superior temporal and lateral inferior precentral gyri followed a non-linear developmental pattern across the measurement sessions. This pattern is reminiscent of previously reported inverted-u-shape developmental trajectories in children’s visual cortical responses to text. Our findings suggest that the processing of letters and speech sounds involves non-linear changes in the brain’s spoken language network possibly related to progressive automatisation of reading skills.
Highlights
Reading is an evolutionary novel, culturally acquired skill that requires us to associate speech with visual symbols
The continuous functional specialisation within this brain region has been proposed to follow an inverted-u-trajectory, showing an increase in activation during early reading instruction followed by a gradual decrease in activation with reading expertise[16]. This pattern of cortical activation in the visual word form area (VWFA) has been reported during the first year of formal reading instruction in response to visual word and letter presentation[15,17], as well as when comparing cortical responses to text longitudinally between kindergarten and second grade vs. adult readers[14]
None of the interaction effects reached significance for the left lateral inferior pre-CG. In this longitudinal Functional magnetic resonance imaging (fMRI) study, we investigated developmental changes in cortical responses to audio-visual letter-speech sound stimuli using a text-based recalibration paradigm in children aged 8–9 to 10–11 years across three measurement time points spaced ~1 year apart
Summary
Reading is an evolutionary novel, culturally acquired skill that requires us to associate speech with visual symbols. The fine-tuning and automatisation of letter-speech sound integration continues while children strengthen their word decoding skills over the first years of reading development[1,4,5,6] During this protracted developmental period, brain areas involved in speech and visual letter processing become increasingly connected both functionally and structurally[7,8,9,10,11]. The continuous functional specialisation within this brain region has been proposed to follow an inverted-u-trajectory, showing an increase in activation during early reading instruction followed by a gradual decrease in activation with reading expertise[16] This pattern of cortical activation in the VWFA has been reported during the first year of formal reading instruction in response to visual word and letter presentation[15,17], as well as when comparing cortical responses to text longitudinally between kindergarten and second grade vs adult readers[14]. To invertedu-shape changes, other types of developmental trajectories, including linear changes, have been observed for e.g. functional responses to speech sounds[20], white matter connectivity[9], and cortical grey- and white matter anatomy[21,22,23,24,25]
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