Neural correlates of orthographic and phonological consistency effects in children

Abstract

The objective of this study was to examine the neural correlates of phonological inconsistency (relationship of spelling to sound) and orthographic inconsistency (relationship of sound to spelling) in visual word processing using functional magnetic resonance imaging (fMRI). Children (9- to 15-year-old) performed a rhyming and spelling task in which two words were presented sequentially in the visual modality. Consistent with previous studies in adults, higher phonological inconsistency was associated with greater activation in several regions including left inferior frontal gyrus and medial frontal gyrus/anterior cingulate cortex. We additionally demonstrated an effect of orthographic inconsistency in these same areas, suggesting that these regions are involved in the integration of orthographic and phonological information and, with respect to the medial frontal/anterior cingulate, greater demands on executive function. Higher phonological and orthographic consistency was associated with greater activation in precuneus/posterior cingulate cortex, the putative steady state system active during resting, suggesting lower demands on cognitive resources for consistent items. Both consistency effects were larger for the rhyming compared with the spelling task suggesting greater demands of integrating spelling and sound in the former task. Finally, accuracy on the rhyming task was negatively correlated with the consistency effect in left fusiform gyrus. In particular, this region showed insensitivity to consistency in low performers, sensitivity to inconsistency (higher activity) in moderate performers, and sensitivity to inconsistency (high activation) and to consistency (deactivation). In general, these results show that the influence of spelling-sound (and sound-spelling) correspondences on processing in fusiform gyrus develops as a function of skill.

Figure 1

Top left (A) shows the trial specifications with the prime stimuli followed by target stimuli presented at a 1 s SOA. The HRF of primes and targets were modeled separately with the conditions of interest being applied to the modeled prime stimuli so as to minimize neural activity because of task specific processing. Top right (B) provides a diagram of the conditions of interest in our 2 (consistency type) by 2 (task) design. These conditions are measured as model coefficients from the item level performed in the single subject fixed‐effect analyses. Bottom (C) reveals the strategy for the analyses reported.

Figure 2

Center images show greater activation for more inconsistent words (hot scale) and greater activation for more consistent words (cold scale) collapsed across consistency type (orthographic and phonological) and task (rhyming and spelling). Regions in the top image include: inferior frontal gyrus (IFG), middle frontal gyrus (MiFG), insula, superior parietal lobule (SPL), inferior parietal lobule (IPL), superior temporal gyrus (STG), middle temporal gyrus (MTG), and fusiform gyrus (FG). Regions in the bottom image include: anterior cingulate cortex (ACC), medial frontal gyrus (MeFG), posterior cingulate cortex (PCC) and precuneus (PreCun). Surrounding graphs show the resulting t‐values of the correlations for each consistency type by each task for individual peaks within the resulting ROIs (threshold value of P < 0.001 uncorrected indicated in green). Conditions defined on the X‐axes for orthographic and phonological consistency for the visual rhyming task (VRO and VRP) and for the visual spelling task (VSO and VSP). Red bars correspond to stronger correlations with more inconsistent words and blue bars correspond to stronger correlations with more consistent words.

Figure 3

(Top row) Regions in which greater activation for more inconsistent words is significantly greater for the rhyming compared to the spelling task. The regions include inferior frontal gyrus (IFG), middle frontal gyrus (MiFG), postcentral gyrus (PostCG), anterior cingulate cortex (ACC), medial frontal gyrus (MeFG), and cingulate gyrus (CG). (Bottom row) Regions in which the greater activation for more consistent words is greater for the rhyming compared to the spelling task. The regions include posterior cingulate cortex (PCC), precuneus (PreCun) and superior parietal lobule (SPL). Color indicates whether task differences were due to phonological consistency (red), orthographic consistency (green) or both (blue).

Figure 4

(Top left) Higher accuracy correlated with greater activation for more inconsistent words in the rhyming task in left fusiform gyrus (FG) for phonological (red) and orthographic (green) consistency (overlap in blue). (Bottom left) Higher accuracy correlated with greater activation for more consistent words in the rhyming task in posterior cingulate cortex/precuneus (PCC/PreCun) for phonological consistency (red). (Right) Graphs display accuracy groups for the top (yellow), middle (red), bottom (blue) third of task performers. Solid lines indicate phonological consistency and dotted lines indicate orthographic consistency. The bottom third of task performers were not sensitive to consistency, whereas better performers were.