Abstract
Reading is considered to be primarily a function of the left hemisphere. However, it is also possible to process text for attributes other than the identity of words and letters, such as the style of font or handwriting. Older anecdotal observations have suggested that processing of handwriting style may involve the right hemisphere. There is also some fMRI evidence of sensitivity to style in either right or left visual word form areas in the fusiform gyri. We created a test that, using the same set of text stimuli, required subjects first to sort text on the basis of word identity and second to sort text on the basis of script style. We presented two versions, one using various computer fonts and the other using the handwriting of different individuals, and measured accuracy and completion times. For testing we selected four subjects with unilateral fusiform lesions and problems with object processing who had been well characterized by neuropsychological testing and structural and/or functional MRI. We found that one alexic subject with left fusiform damage performed well when sorting by script style but had markedly prolonged reading times when sorting by word identity. In contrast, two prosopagnosic subjects with right lateral fusiform damage that eliminated the fusiform face area and likely the right visual word form area were impaired in sorting for script style, but performed better when sorting for word identity. Another prosopagnosic subject with right medial occipitotemporal damage sparing areas in the lateral fusiform gyrus performed well on both tasks. The contrast in the performance of patients with right versus left fusiform damage suggests an important distinction in hemispheric processing that reflects not the type of stimulus but the nature of the processing operations required.
CIHR grant MOP-77615, Alzheimer Society of Canada, Michael Smith Foundation for Health Research, Canada Research Chair program.