Left hemisphere specialization for word reading potentially causes, rather than results from, a left lateralized bias for high spatial frequency visual information

There is considerable evidence showing that efficient visual word recognition relies on high spatial frequency (HSF) visual coding in the left posterior fusiform gyrus. But whether the bias for HSF in the left hemisphere (LH) causally contributes to the LH superiority for word recognition or possibly results from it remains unknown. To assess whether the lateralization for HSF information exists prior to the left lateralization for reading, we used a divided-visual field task to examine the LH bias for orthographic processing and for HSF Gabor patches in young children (mean age 4.5 years) with variable letter knowledge, and in adults. If LH specialization for orthographic processing results from a pre-existing HSF bias in the LH, then LH specialization for HSF information should be evident even in those young children with minimal, if any, letter knowledge. The adult participants showed the predicted LH lateralization for both HSF information and word recognition. Neither of these hemispheric biases, however, was statistically significant in the group of young children. Further investigation, however, revealed a correlation between these biases such that those children with the somewhat more developed LH advantage for orthographic representations also evinced an LH bias for HSF information. These findings suggest that, rather than serving as a precursor for the LH superiority for word recognition, the LH bias for HSF input might emerge in concert with it or potentially even be a consequence of the acquisition of orthographic competence.