Now They See It, Now They Don't: Lateralities of the Seeing Hand and Neglect

摘要

In this study, "the seeing hand," has literal and figurative meanings. Literally, "the seeing hand" is the hand that restores vision to the nondominant side of the space which was denied to the patient had he or she been using the other hand instead. Figuratively, using the nondominant hand temporarily restores the ability to recognize one's own deficit following lesions affecting the minor hemisphere (i.e. it provides insight as to their "hemianopia" and anosognosia). It is shown that failure to recognize that speech is the marker of the hemisphere of action (where all commands are issued regardless of the laterality of the intended effectors) has been the basis for ignoring the role of latency differential in moving the eyes to the side as the mechanism for right visual field advantage in lexical decision making and similar paradigms in right handed subjects. The data reviewed show that nondominant somatosensory signals are destined to the major hemisphere for conscious apprehension after they arrived to the parietal lobe in the minor hemisphere. The data indicates that, contrary to the current beliefs, callosum carries no primary visual signals and macular vision occurs exclusively in the major hemisphere.