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It Is All Quiet in the Minor Hemisphere: An Investigation into the Laterality of Consciousness, Attention and Vision in the Human Brain

Iraj Derakhshan

Abstract


This is a meta-analysis of the literature on laterality of motor control in relation to vision, neglect and attention. It documents the role of directionality of signal transfer between the two hemispheres. By indexing cases in which macular vision was spared or damaged in lesions affecting the minor or major hemispheres, respectively, we show that the minor hemisphere’s role is to dilate (extend) the space in which vision occurs rather than providing for the elementary aspects of vision. We review the statistical relationship between the laterality of seeing and speaking and that of behavioral handedness of subjects, in studies employing inspection time and lexical decision paradigms; the distinction between the two modes of handedness (i.e. behavioral and neural) is defined. We provide evidence that brainedness (i.e. the laterality of the executive hemisphere) encompasses the destination of all signals relating to consciousness, and that the minor hemisphere relates to three-dimensional (3-D) spatial awareness. However, 3-D spatial awareness relies on signals travelling from the nondominant side of the body/space to the major hemisphere via the posterior aspect of the callosum, which may explain why neglect occurs exclusively in lesions affecting the minor hemisphere, as defined in this article.  This is a comprehensive review of clinical, neuropathological and physiological data, and indicates that macular vision occurs in the major hemisphere and that handedness is a reflection of the laterality of conscious awareness.


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