Differential activation of the visual word form area during auditory phoneme perception in youth with dyslexia

Abstract

Developmental dyslexia is a learning disorder characterized by difficulties reading words accurately and/or fluently. Several behavioral studies have suggested the presence of anomalies at an early stage of phoneme processing, when the complex spectrotemporal patterns in the speech signal are analyzed and assigned to phonemic categories. In this study, fMRI was used to compare brain responses associated with categorical discrimination of speech syllables (P) and acoustically matched nonphonemic stimuli (N) in children and adolescents with dyslexia and in typically developing (TD) controls, aged 8-17 years. The TD group showed significantly greater activation during the P condition relative to N in an area of the left ventral occipitotemporal cortex that corresponds well with the region referred to as the "visual word form area" (VWFA). Regression analyses using reading performance as a continuous variable across the full group of participants yielded similar results. Overall, the findings are consistent with those of previous neuroimaging studies using print stimuli in individuals with dyslexia that found reduced activation in left occipitotemporal regions; however, the current study shows that these activation differences seen during reading are apparent during auditory phoneme discrimination in youth with dyslexia, suggesting that the primary deficit in at least a subset of children may lie early in the speech processing stream and that categorical perception may be an important target of early intervention in children at risk for dyslexia.

Keywords: Developmental dyslexia; Phoneme perception; Reading development; Speech perception; Visual word form area.

Figure 1.

Discrimination functions for the typically developing control group and the group with dyslexia in the Phonemic and Nonphonemic conditions. Error bars reflect standard error of measurement.

Figure 2.

Regions showing significant group differences in the whole-brain analyses in the (A) Phonemic condition relative to Baseline and in the (B) Phonemic relative to the Nonphonemic condition. Hot colors indicate greater activation in the typically developing controls than the group with dyslexia, and cool colors indicate the reverse. A graph of the simple effects is also shown for the latter contrast.

Figure 3.

Relationships between the Reading Composite and activation in the Phonemic condition relative to the Nonphonemic condition across the full sample while controlling for age and scanner type, showing clusters in the medial frontal cortex (A and B) and left occipitotemporal cortex (C and D).

Figure 4.

Relationships between age-residualized CPI scores and activation in the left vOTC in the Phonemic relative to the Nonphonemic condition in low performing and high performing readers.