Neurodevelopmental trajectories of audiovisual (AV) letter processing.

Measurements at five time points from preschool across primary school with fMRI.

Activation in ventral occipitotemporal cortex followed a complex trajectory.

Activation in superior temporal gyrus followed an inverted U-shaped development.

Trajectories for AV processing and integration were modulated by reading skills.

Learning to read alphabetic languages starts with learning letter–speech-sound associations. How this process changes brain function during development is still largely unknown. We followed 102 children with varying reading skills in a mixed-longitudinal/cross-sectional design from the prereading stage to the end of elementary school over five time points (n = 46 with two and more time points, of which n = 16 fully-longitudinal) to investigate the neural trajectories of letter and speech sound processing using fMRI. Children were presented with letters and speech sounds visually, auditorily, and audiovisually in kindergarten (6.7yo), at the middle (7.3yo) and end of first grade (7.6yo), and in second (8.4yo) and fifth grades (11.5yo). Activation of the ventral occipitotemporal cortex for visual and audiovisual processing followed a complex trajectory, with two peaks in first and fifth grades. The superior temporal gyrus (STG) showed an inverted U-shaped trajectory for audiovisual letter processing, a development that in poor readers was attenuated in middle STG and absent in posterior STG. Finally, the trajectories for letter-speech-sound integration were modulated by reading skills and showed differing directionality in the congruency effect depending on the time point. This unprecedented study captures the development of letter processing across elementary school and its neural trajectories in children with varying reading skills.

Audiovisual integration

Superior temporal gyrus

Visual word form area

FMRI

The data supporting the conclusions of this article will be made available by the authors upon reasonable request. Some restrictions may apply for data sharing due to the restricted consent of research participants. Scripts are available via Open Science Framework (OSF), https://doi.org/10.17605/OSF.IO/FWM6R.

© 2023 The Authors. Published by Elsevier Ltd.