The "special effect" of case mixing on word identification: neuropsychological and transcranial magnetic stimulation studies dissociating case mixing from contrast reduction.

We present neuropsychological and transcranial magnetic stimulation (TMS) evidence with normal readers, that the effects of case mixing and contrast reduction on word identification are qualitatively different. Lesions and TMS applied to the right parietal lobe selectively disrupted the identification of mixed relative to single-case stimuli. Bilateral lesions and TMS applied to the occipital cortex selectively disrupted the identification of low-contrast words. These data suggest that different visual distortions (case mixing, contrast reduction) exert different effects on reading, modulated by contrasting brain regions. Case mixing is a "special" distortion and involves the recruitment of processes that are functionally distinct, and dependent on different regions in the brain, from those required to deal with contrast reduction.