Brain sensitivity to print emerges when children learn letter-speech sound correspondences

Abstract

The acquisition of reading skills is a major landmark process in a human's cognitive development. On the neural level, a new functional network develops during this time, as children typically learn to associate the well-known sounds of their spoken language with unfamiliar characters in alphabetic languages and finally access the meaning of written words, allowing for later reading. A critical component of the mature reading network located in the left occipito-temporal cortex, termed the "visual word-form system" (VWFS), exhibits print-sensitive activation in readers. When and how the sensitivity of the VWFS to print comes about remains an open question. In this study, we demonstrate the initiation of occipito-temporal cortex sensitivity to print using functional MRI (fMRI) (n = 16) and event-related potentials (ERP) (n = 32) in a controlled, longitudinal training study. Print sensitivity of fast (<250 ms) processes in posterior occipito-temporal brain regions accompanied basic associative learning of letter-speech sound correspondences in young (mean age 6.4 +/- 0.08 y) nonreading kindergarten children, as shown by concordant ERP and fMRI results. The occipito-temporal print sensitivity thus is established during the earliest phase of reading acquisition in childhood, suggesting that a crucial part of the later reading network first adopts a role in mapping print and sound.

Fig. 1.

Implicit audiovisual word and false font/rotated speech-processing task, divided into two separate parts: unimodal and bimodal word (Upper) and false font/rotated speech presentation (Lower). Children had to indicate whether a stimulus was presented visually (V), auditorily (A), or audiovisually (AVc/AVi), by pressing response buttons.

Fig. 2.

Emerging print sensitivity seen as differential fMRI activation to words and false fonts and projected onto a pediatric brain template (Left) and on three sections (k ≥ 0) of the mean structural image of the group (Right). (A) fMRI activation to words (orange) and false fonts (blue) for the whole fMRI sample (n = 16) before (Pre) and after (Post) GG training (Upper two rows) or NC training (Lower two rows). For both conditions, Pre- and Post-training activity was predominantly bilateral occipito-temporal. Note that no difference was detected for words vs. false font stimuli between Pre-GG and Pre-NC, but slight group differences in the right inferior occipital gyrus were found between the fMRI subgroups at T1 (Fig. S3). (B) Interaction (two-factorial ANOVA) of training (GG, NC) and time (Pre, Post) revealed areas with more pronounced activity for the word–false font contrast after GG but not after NC training (green). On the lateral views (Left), Post vs. Pre GG training of W-FF is superimposed in yellow.

Fig. 3.

ROI analyses along the occipito-temporal cortex. Mean percent signal change (error bars, ±1 SEM) for the GG-first (Upper) and NC-first (Lower) groups in five consecutive spherical ROIs plotted at each test time for the left hemisphere (Fig. S4). The location of the five ROIs is illustrated on the axial slice at the left. Significant training effects (*) were detected in R4.

Fig. 4.

Print-sensitive ERP activity in the visual N1 after GG training. (A) Training effects on the N1 (189–295 ms) at LOT sites for the GG-first (Upper) and NC-first (Lower) groups, respectively. Waveforms after GG training are plotted with thicker lines. Print sensitivity emerged as a pronounced difference in amplitude between W and FF in the N1 interval after GG training. (B) Statistical N1 ERP t-maps illustrating the W–FF contrast for the GG-first (Left) and NC-first (Right) groups. According to TANOVA, W and FF map topographies differed after GG training at T2 for the GG-first group and at T3 for both groups. *, P < .05; ⁽*⁾, P < 0.1). Green arrows illustrate periods with GG training. (C) Estimated N1 Post- vs. Pre-GG sources for W–FF in the occipito-temporal cortex and right cuneus.