Individual variability in location impacts orthographic selectivity in the "visual word form area"

Abstract

Strong evidence exists for a key role of the human ventral occipitotemporal cortex (vOT) in reading, yet there have been conflicting reports about the specificity of this area in orthographic versus nonorthographic processing. We suggest that the inconsistencies in the literature can be explained by the method used to identify regions that respond to words. Here we provide evidence that the "visual word form area" (VWFA) shows word selectivity when identified at the individual subject level, but that intersubject variability in the location and size of the VWFA causes this selectivity to be washed out if defining the VWFA at the group level or based on coordinates from the literature. Our findings confirm the existence of a word-selective region in vOT while providing an explanation for why other studies have found a lack of word specificity in vOT.

Figure 1.

ROI variability. Lateral (A) and superior (B) views of the brain, along with a blow-up of the relevant regions (red frame) showing gROI (solid red blob), litROI (solid blue blob), and iROI (translucent blobs, N = 53).

Figure 2.

The VWFA is selective for orthography, but only if defined individually. Average percentage signal change to words, objects and faces in the left hemisphere in three ROIs: the literature based ROI (litROI), group-based ROI (gROI), and individually defined ROI (iROI) for (A) the main experiment and (B) the control experiment. Error bars represent within-subject SEM.

Figure 3.

Whole-brain analysis and effect of varying ROI size. A, Whole-brain analysis of words > objects contrast. Crosshair is centered at the location of the classically defined VWFA (Talairach coordinates −43 −54 −12 (Cohen et al., 2002) MNI −45 −57 −12 (Vogel et al., 2012). Color bar shows t values. B, Effect of changing the size of gROI and litROI in the main experiment and (C) control experiment. Plots show mean percentage signal change to words, objects, and faces in the left hemisphere gROI and litROI for varying ROI sizes. **Indicates the ROI reported on in Figure 2. Error bars represent within-subject SEM.