Laterality for recognizing written words and faces in the fusiform gyrus covaries with language dominance

Abstract

Recognizing words and faces engages highly specialized sites within the middle fusiform gyrus, known as the visual word form area (VWFA) and fusiform face area (FFA) respectively. The VWFA and FFA have clear but opposite population-level asymmetries, with the VWFA typically being lateralized to the left and the FFA to the right hemisphere. The present study investigates how language dominance may relate to these asymmetries. We hypothesize that individuals with left hemisphere dominance for word production (i.e., left language dominance, LLD) will have typical lateralization for word and face recognition in the fusiform gyrus, whereas participants with right language dominance (RLD) will demonstrate 'atypical' rightward laterality for words and leftward dominance for faces. To test this hypothesis, we recruited twenty-seven left-handers who had previously been identified as being LLD or RLD based on a visual half field task. Using fMRI, hemisphere dominance was determined for language (Broca's region) as well as for word and face recognition in the middle fusiform gyrus for each participant. The direction of asymmetry correlated significantly between language and recognizing words (ρ = .648, p < .001) as well as between language and face recognition (ρ = -.620, p = .001). Moreover, most LLD-participants were typically lateralized for faces and written words, while both functions tended to be reversed in individuals with RLD. However, segregation between language and face recognition was less clear in participants with RLD, as many of them lacked an obvious asymmetry for faces. Although our results thus suggest there is no one-on-one relationship between asymmetries for language, written word and face recognition, they also argue against a complete independence of their lateralization.

Keywords: Brain asymmetry; Face recognition; Language dominance; Lateralization; Reading.