Development of brain mechanisms for processing orthographic and phonologic representations

Abstract

Developmental differences in the neurocognitive networks for lexical processing were examined in 15 adults and 15 children (9- to 12-year-olds) using functional magnetic resonance imaging (fMRI). The lexical tasks involved spelling and rhyming judgments in either the visual or auditory modality. These lexical tasks were compared with nonlinguistic control tasks involving judgments of line patterns or tone sequences. The first main finding was that adults showed greater activation than children during the cross-modal lexical tasks in a region proposed to be involved in mapping between orthographic and phonologic representations. The visual rhyming task, which required conversion from orthography to phonology, produced greater activation for adults in the angular gyrus. The auditory spelling task, which required the conversion from phonology to orthography, also produced greater activation for adults in the angular gyrus. The greater activation for adults suggests they may have a more elaborated posterior heteromodal system for mapping between representational systems. The second main finding was that adults showed greater activation than children during the intra-modal lexical tasks in the angular gyrus. The visual spelling and auditory rhyming did not require conversion between orthography and phonology for correct performance but the adults showed greater activation in a system implicated for this mapping. The greater activation for adults suggests that they have more interactive convergence between representational systems during lexical processing.

Figure 1

Significant activation for the adults and children on the spelling (S) and rhyming (R) tasks in the visual (V) and auditory (A) modalities. These slices show activation for the adults (red), for the children (green), and for both adults and children (purple).

Figure 2

Significant differences between the adults and children activation on the spelling (S) and rhyming (R) tasks in the visual (V) and auditory (A) modalities. These slices show significantly greater activation for the adults (red) or for the children (green). Only clusters in our regions of interest are labeled (see Tables 4, 5, 6, and 7 for all significant regions). Slices were chosen to maximize visualization of clusters while selecting similar z-coordinates across tasks (AG = angular gyrus; FG = fusiform gyrus; IFG = inferior frontal gyrus; MTG = middle temporal gyrus; STG = superior temporal gyrus).