Foveal

About: Foveal is a research topic. Over the lifetime, 2652 publications have been published within this topic receiving 94120 citations.

Dependence of visual stabilization of postural sway on the cortical magnification factor of restricted visual fields.

Abstract: Monocular visual stabilization of fore-aft and lateral body sway was tested posturographically in normal subjects (wearing visual field blinds) as a function of visual field size and location of the visual field on the central or peripheral retina. Body sway applied to a force- measuring platform is less with central (foveal) vision when central and peripheral visual fields have the same area. If, however, the peripheral field size is corrected by the cortical magnification factor of the retina in the primary cortex, body sway is stabilized by the peripheral retina to the same extent. Thus, there is no functional specialization of central and peripheral retina with respect to balance control. Visual stabilization of upright stance is a function of field size and cortical representation of the retina. The central and the peripheral retina have different thresholds to detect motion; this was surprisingly not reflected in measurements of normal fore-aft and lateral body sway.

A Magnetic Stimulation Examination of Orthographic Neighborhood Effects in Visual Word Recognition

Abstract: The split-fovea theory proposes that visual word recognition is mediated by the splitting of the foveal image, with letters to the left of fixation projected to the right hemisphere (RH) and letters to the right of fixation projected to the left hemisphere (LH). We applied repetitive transcranial magnetic stimulation (rTMS) over the left and right occipital cortex during a lexical decision task to investigate the extent to which word recognition processes could be accounted for according to the split-fovea theory. Unilateral rTMS significantly impaired lexical decision latencies to centrally presented words, supporting the suggestion that foveal representation of words is split between the cerebral hemispheres rather than bilateral. Behaviorally, we showed that words that have many orthographic neighbors sharing the same initial letters ("lead neighbors") facilitated lexical decision more than words with few lead neighbors. This effect did not apply to end neighbors (orthographic neighbors sharing the same final letters). Crucially, rTMS over the RH impaired lead-, but not end-neighborhood facilitation. The results support the split-fovea theory, where the RH has primacy in representing lead neighbors of a written word.

How Humans Reach: Distinct Cortical Systems for Central and Peripheral Vision

Abstract: Lesions of the posterior parietal cortex in humans can produce a specific disruption of visually guided hand movements termed optic ataxia. The fact that the deficit mainly occurs in peripheral vision suggests that reaching in foveal and extrafoveal vision relies on two different anatomical substrates. Using fMRI in healthy subjects, the authors demonstrated the existence of two systems, differently modulated by the two reaching conditions. Reaching in central vision involves a restricted network, including the medial intraparietal sulcus (mIPS) and the caudal part of the dorsal premotor cortex (PMd). Reaching in peripheral vision engages a more extensive network, including the parieto-occipital junction (POJ). Interestingly, POJ corresponds to the site of the lesion overlap that the authors recently found to be responsible for optic ataxia. These two sets of results converge to show that there is not a unique cortical network for reaching control but instead two systems engaged in reaching to targets in the central and peripheral visual field.