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Vertical scanning biases and their possible influence on reading direction: Celtic wisdom or folly?
- ALEJANDRA M. AMENGUAL, VALERIA DRAGO, PAUL S. FOSTER, RAMON C. LEIGUARDA, KENNETH M. HEILMAN
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- Journal:
- Journal of the International Neuropsychological Society / Volume 14 / Issue 1 / January 2008
- Published online by Cambridge University Press:
- 14 December 2007, pp. 102-109
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- Article
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The reason people read from top to bottom is unknown, but could be related to brain-mediated directional biases or environmental factors. To learn if there is a brain-mediated directional bias responsible for top–down reading direction, we evaluated the directional scanning in the vertical dimension by using directional letter and face cancellation tasks. Twenty participants were instructed to cancel either target letters or faces using either an up–down or down–up direction, with the stimuli located in left, right, and center hemispace. The results indicated significant differences in completion time between the search direction (up vs. down) and spatial position for the letter cancellation task, with a faster completion time for the bottom–up scan in right space and top–down in left space. Because the left hemisphere primarily attends to contralateral right hemispace our results suggest that, when attending to letter stimuli, the left hemisphere is biased to scan in a proximal to distal (upward) direction. Although the reasons why this is reversed in left hemispace and why we did not see directional biases in the face condition remains unclear, these results do suggest that the direction in which we learn to read is inconsistent with the brain's intrinsic directional bias. (JINS, 2008, 14, 102–109.)
32 - The apraxias
- from PART III - DISORDERS OF MOTOR CONTROL
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- By Ramón C. Leiguarda, Raúl Carrea Institute of Neurological Research, FLENI, Buenos Aires, Argentina
- Edited by Arthur K. Asbury, University of Pennsylvania School of Medicine, Guy M. McKhann, The Johns Hopkins University School of Medicine, W. Ian McDonald, University College London, Peter J. Goadsby, University College London, Justin C. McArthur, The Johns Hopkins University School of Medicine
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- Book:
- Diseases of the Nervous System
- Published online:
- 05 August 2016
- Print publication:
- 11 November 2002, pp 462-476
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Summary
Apraxia is a term used to denote a wide spectrum of higherorder motor disorders owing to acquired brain disease affecting the performance of skilled, learned movements with or without preservation of the ability to perform the same movement outside the clinical setting in the appropriate situation or environment. The disturbance of purposive movements cannot be termed apraxia, however, if it results from a language comprehension disorder or from dementia, or if the patient suffers from any elementary motor or sensory deficit (i.e. paresis, dystonia, ataxia) which could fully explain the abnormal motor behaviour (Heilman & Rothi, 1985; Roy & Square, 1985; De Renzi, 1989). The praxic disorder may affect various body parts such as the eyes, face, trunk, or limbs, and may involve both sides of the body (i.e. ideational and ideomotor apraxias), preferentially one side (i.e. limb-kinetic apraxia), or, alternatively, interlimb coordination, as in the case of apraxia of gait.
Apraxias are poorly recognized but common disorders that can result from a wide variety of focal (i.e. stroke, trauma) or diffuse brain damage (i.e. corticobasal degeneration, Alzheimer's disease) (Heilman & Rothi, 1985; Freund, 1992). There are two main reasons why apraxia may go unrecognized. Firstly, many patients with apraxia, particularly ideomotor apraxia, show a voluntary–automatic dissociation, which means that the patient does not complain about the deficit because the execution of the movement in the natural context is relatively well preserved, and the deficit appears mainly in the clinical setting when the patient is required to represent explicitly the content of the action outside the situational props. Secondly, although in apraxic and aphasic patients specific functions are selectively affected, language and praxic disturbances frequently coexist and the former may interfere with the proper evaluation of the latter (Freund, 1992).
Limb apraxias
Liepmann (1920) posited that the idea of the action, or movement formula, containing the space–time form picture of the movement, was stored in the left parietal lobe. In order to carry out a skilled movement, the space–time plan has to be retrieved and associated via cortical connections with the innervatory pattern stored in the left sensorimotorium that conveys the information to the left primary motor area. When the left limb performs the movement, the information has to be transmitted from the left to the right sensorimotorium through the corpus callosum to activate, thereafter, the right motor cortex.