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LETTER TO THE EDITOR
responded to a study conducted by Gonzalez and colleagues (2006a) that explored a potential hemispheric specialization for the visual control of action independent of subject handedness. In his letter, Dr. Derakshan suggested that an important variable of concern, which was measured but not reported by Gonzalez et al., is that of reaction time. In this case, it was argued that this measure is an effective means of determining in which cerebral hemisphere (right vs. left) lies the "control center" for movement, based on the side of the body that can be more rapidly brought into motion.
In reply to this request Gonzalez et al. (2006b) emphasized that the visuomotor advantage they reported was distinctly different from any notion of a hemispheric dominance for a command center and that movements in their study were not speeded, thus rendering reaction time measures unreliable. Although I fully accept this response, I feel compelled to express my own concern for the efficacy of using simple reaction time measures as a means of determining "neural handedness" or the location of the motor center. Certainly, Dr. Derakshan provided substantial evidence from clinical sources indicating a correlation between left hemisphere laterality and right-hand leading when comparing left- and right-hand reaction times in right-handed individuals. However, ignored in this argument are the results from two decades of study in the area of motor control that have consistently generated the contradictory result—a left-arm (right-hemisphere) reaction time advantage in the preparation and execution of movements made by right-handed individuals (Barthélémy and Boulinguez 2001, 2002; Boulinguez and Nougier 1999; Bradshaw et al. 1990; Carson et al. 1990, 1993, 1995; Velay et al. 1999, 2001).
Although the simplicity of measuring reaction time makes it an attractive means of assessing motor laterality, given the polarity of results from clinical and motor control approaches to study, it is difficult to endorse such a practice. Rather, a more involved process of determining limb/hemisphere specialization is likely necessary, including a mixture of hand-preference scales and limb-performance measures in association with brain-imaging techniques.
REFERENCES
Barthélémy S, Boulinguez P. Manual reaction time asymmetries in human subjects: the role of movement planning and attention. Neurosci Lett 315: 41–44, 2001.[CrossRef][ISI][Medline]
Barthélémy S, Boulinguez P. Manual asymmetries in the directional coding of reaching: further evidence for hemispatial effects and right hemisphere dominance for movement planning. Exp Brain Res 147: 305–312, 2002.[CrossRef][ISI][Medline]
Boulinguez P, Nougier V. Control of goal-directed movements: the contribution of orienting of visual attention and motor preparation. Acta Psychol (Amst) 103: 21–45, 1999.
Bradshaw JL, Bradshaw JA, Nettleton NC. Abduction, adduction and hand differences in simple and serial movements. Neuropsychologia 28: 917–931, 1990.[CrossRef][ISI][Medline]
Carson RG, Chua R, Goodman D, Byblow WD, Elliott D. The preparation of aiming movements. Brain Cogn 28: 133–154, 1995.[CrossRef][ISI][Medline]
Carson RG, Elliott D, Goodman D, Dickinson J. Manual asymmetries in the reproduction of a 3-dimensional spatial location. Neuropsychologia 28: 99–103, 1990.[CrossRef][ISI][Medline]
Carson RG, Goodman D, Chua R, Elliott D. Asymmetries in the regulation of visually guided aiming. J Mot Behav 25: 21–32, 1993.[ISI][Medline]
Derakhshan I. Laterality of the command center in relation to handedness and simple reaction time: a clinical perspective [Letter to the Editor]. J Neurophysiol 96: 3556, 2006.
Gonzalez CL, Ganel T, Goodale MA. Hemispheric specialization for the visual control of action is independent of handedness. J Neurophysiol 95: 3496–3501, 2006a.
Gonzalez CL, Ganel T, Goodale MA. Reply. J Neurophysiol 96: 3557, 2006b.
Velay JL, Benoit-Dubrocard S. Hemispheric asymmetry and interhemispheric transfer in reaching programming. Neuropsychologia 37: 895–903, 1999.[CrossRef][ISI][Medline]
Velay JL, Daffaure V, Raphael N, Benoit-Dubrocard S. Hemispheric asymmetry and interhemispheric transfer in pointing depend on the spatial components of the movement. Cortex 37: 75–79, 2001.[ISI][Medline]
Daniel Goble
Motor Control Laboratory
Division of Kinesiology
University of Michigan
Ann Arbor
Michigan 48109-2214
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