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.

Developmental changes in brain regions involved in phonological and orthographic processing during spoken language processing

“…These studies have provided a relatively consistent picture, showing activation in left inferior frontal gyrus and bilateral superior temporal gyrus (Booth, et al 2002;Burton, et al 2003;Burton, et al 2005;Rudner, et al 2005). Right superior temporal gyrus activation has been linked to perception of pitch variation in linguistic and nonlinguistic stimuli (Johnsrude, et al 2000;Scott, et al 2000).…”

“…We expected that we might observe activation, as well as potential developmental increases, in these regions because they have been implicated in phonological processes (Binder, et al 1994) and mapping between orthographic and phonological representations (Booth, et al 2002;Booth, et al 2003a), respectively. The lack of such effects in these regions may result from the relatively little demands on phonological processing required by our rhyming task or because the task relied on auditory processing regions shared by the perceptual control (which was used as an exclusive mask).…”

“…Activation in left inferior frontal gyrus may reflect reliance on phonological segmentation processes (Hagoort, et al 1999), increasing activation of motor programs involved in planning articulations (Rizzolatti and Craighero 2004) and/or greater top-down modulation of posterior regions associated with phonological processing (Bitan, et al 2005). Some studies using an auditory rhyme decision task have additionally shown activation in right inferior frontal gyrus (Burton, et al 2003;Rudner, et al 2005), left fusiform gyrus (Booth, et al 2002;Burton, et al 2003;Burton, et al 2005), and either bilateral inferior parietal lobules (Rudner, et al 2005) or left angular gyrus (Burton, et al 2003). Studies of visual word processing have implicated left fusiform gyrus in orthographic processing McCandliss, et al 2003).…”

“…Activation of left fusiform gyrus during an auditory lexical task suggests that orthographic representations may be automatically accessed even when access to these representations is not required for correct performance. Previous neuroimaging studies have implicated inferior parietal cortex in mapping between orthographic and phonological representations (Booth, et al 2002;Booth, et al 2003a), and studies of developmental and acquired dyslexia have identified inferior parietal cortex as a common site for underactivation or lesions associated with these disorders (see Pugh, et al 2000). Thus, activation in the inferior parietal cortex during auditory rhyme decision tasks may reflect the process of mapping between phonological representations in superior temporal gyrus and orthographic representations in fusiform cortex, a process essential to reading.…”

“…Although neither adults nor children showed significant activation relative to a control task in left angular gyrus in a rhyming task (Booth, et al 2004), adults showed significantly greater activation than children in this region when directly comparing the two age groups. Because left inferior parietal cortex has been implicated in mapping between orthographic and phonological representations (Booth, et al 2002;Booth, et al 2003a), greater activation in this region by adults may indicate more automatic mapping to orthographic representations during spoken word processing by adults than by children.…”