Examination of the split fovea theory in a case of pure left hemialexia

Abstract

To address the extent to which the visual foveal representation is split, we examine the case of a patient, M.B., suffering from a left mesial occipital lesion and presenting a pure left hemialexia and a right hemianopia with a spared area of the macula. Reading performance on tachistoscopically presented four-letter words and pseudowords in the spared area of the right visual field was significantly better than reading performance in the intact left visual field. Reading performance in the spared area of the right visual field was also significantly better than reading performance of stimuli centred on the fovea. Moreover, a length effect was found only in the left half of pseudowords centred on the fovea, but not in the right half (up to five letters). These differences in reading efficiency between the left and right halves of the foveal region militates in favour of the split fovea theory and cannot be explained by the bilateral projection theory.

Functional Foveal Splitting: Evidence from Neuropsychological and Multimodal MRI Investigations in a Chinese Patient with a Splenium Lesion

“…Therefore, subjects with disconnected communications between posterior hemispheres, such as patients with splenium lesion or commissurotomy, provide a unique opportunity to tease apart mixed accounts for cortical representations of foveal vision. Sieroff & Lavidor adopted reading tasks to test a patient with left medial occipital lesion which the author suggested to injure the splenium, and found evidence supporting SFT [59]. Unfortunately the authors did not use relatively direct imaging methods such as high resolution structural image or DTT (diffusion-tensor tractography) to confirm the disruption of the splenium.…”