Longitudinal changes in cortical responses to letter-speech sound stimuli in 8–11 year-old children

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.

Neurodevelopmental trajectories of letter and speech sound processing from preschool to the end of elementary school

“…Activation during audiovisual processing showed an inverted U-shaped development within the STG and the lateral precentral gyri for children aged 8 years at the first measurement and a linear development for children aged 9 years at the first measurement. Whereas we observed the peak of activation in the STG at around 7.5 years, the peak in activation reported by Romanovska et al (2022) was at a later age, 9.8 years. It is likely that this discrepancy can be explained by the methodological differences between the two studies.…”

“…The inverted U-shaped development of VWFA activation to print has also been observed with functional magnetic resonance imaging (fMRI) measurements ( Dehaene-Lambertz et al, 2018 ). Similarly, the left STG and left lateral inferior precentral gyrus show an inverted U-shaped development during audiovisual processing in 8–11-year-old children ( Romanovska et al, 2022 ).…”

“…Using fMRI recordings collected during an implicit target detection task and by applying a combined longitudinal and cross-sectional analyses approach, we compared brain activation to visual, auditory, and audiovisual stimuli over five time points in kindergarten, first grade (two time points), second grade, and fifth grade of primary school in children with varying reading skills. From previous studies ( Fraga-González et al, 2021 , Karipidis et al, 2021 , Maurer et al, 2006 , Romanovska et al, 2022 ) and current models of skill learning and specialization ( Lövdén et al, 2020 , Price and Devlin, 2011 , Wenger et al, 2017 ), we expected inverted U-shaped developments for the activation of auditory, visual, and audiovisual letter processing within temporal and vOTC regions of the reading network, with an activation increase from kindergarten, before the start of formal reading instruction, to first grade when children start to learn letter–speech-sound correspondences, and a decline in activation after initial consolidation of correspondences up to fifth grade. Given that inverted U-shaped trajectories might represent a change from effortful letter-by-letter processing to automatized reading, we presume that these developmental trajectories are modulated by children’s reading skills.…”

“…However, full automatization of letter–speech-sound associations and the corresponding maturation of the underlying brain systems is a lengthy process that takes several years ( Dehaene et al, 2015 , Froyen et al, 2009 ). To date, few studies have investigated and characterized changes in functional brain activation during the development of single-letter and speech-sound processing and in parallel with reading acquisition ( Blackburne et al, 2014 , Caffarra et al, 2021 , Cantlon et al, 2011 , Centanni et al, 2018 , Fraga-González et al, 2021 , Froyen et al, 2009 , Karipidis et al, 2018 , Karipidis et al, 2021 , Pleisch et al, 2019 , Plewko et al, 2018 , Romanovska et al, 2022 , Zaric et al, 2015 ).…”

The Use of Neuronal Response Signals as Early Biomarkers of Dyslexia

“…These experiments have revealed that deviations in the ERP signal, about 200 ms after stimulus onset, correlate with visual-orthographic processing and occur over the left occipital-temporal cortex (Maurer & McCandliss, 2008;Michel et al, 2004;Rossion et al, 2002;Tarkiainen et al, 1999). The findings of this signal have been used to identify the emergence of literacy by measuring the variations in neuronal activity as a function of literacy training in children (Maurer et al, 2006;Romanovska et al, 2022). In addition to the analysis of auditory and visual processing, electrophysiological investigations have determined that ERP signals near 400 ms post stimulus correlate with semantic evaluation (Deacon et al, 2000;Gomes et al, 1997;Holcomb, 1988;Kutas & Hillyard, 1984;Morgan et al, 2020).…”