Asymmetries in the Preparation and Control of Manual Aiming Movements

Abstract Two experiments were conducted to determine if typical right hand target aiming advantages could be reduced or eliminated by increasing the spatial demands of the aiming task. In Experiment 1, we found right hand advantages for both movement time and error regardless of spatial characteristics of the task. When we introduced a greater degree of spatial uncertainty in Experiment 2, subjects exhibited a left hand reaction time advantage. Taken together our results suggest that the right cerebral hemisphere may have a special role to play in preparing the spatial aspects of an aiming movement, while the left hemisphere is more important for movement execution.Resume Deux experiences ont ete effectuees afin de determiner si l'augmentation des demandes spatiales de la ta@che de visee pouvait reduire ou eliminer les avantages typiquement relies a la main droite lorsque celle - ci s'oriente vers une cible. Dans l'experience 1, nous avons observe des avantages relies a la main droite pour ce qui est de la duree du mouvement et de la marge d'erreur, peu importe les caracteristiques spatiales de la ta@che. Dans l'experience 2 ou le degre d'incertitude spatiale etait plus eleve, nous avons observe chez les sujets un avantage relie a la main gauche et au temps de reaction. Mis ensemble, les resultats laissent supposer que l'hemisphere cerebral droit pourrait jouer un ro@le particulier dans la preparation des aspects spatiaux des mouvements diriges vers une cible, tandis que l'hemisphere gauche serait plus important pour l'execution des mouvements.Asymmetries in the performance of various manual tasks are often attributed to the proficiency of the contralateral cerebral hemisphere for specific types of processing (Todor & Smiley, 1985). For example, right - hand advantages for finger sequencing (Edwards & Elliott, 1987) and rapid finger tapping (Todor, Kyprie, & Price, 1982) have been ascribed to left hemisphere specialization for the organization and control of sequential movement. Left side superiority for tasks involving tactile discrimination (Benton, Varney, & deHamsher, 1976; Witelson, 1974) and kinesthetic spatial judgements (Carnahan & Elliott, 1987; Roy & MacKenzie, 1978) are thought to result from a right hemisphere propensity for spatial processing. Of interest here is how the cerebral hemispheres might interact or share responsibility to ensure optimal performance in motor tasks such as reaching and aiming which entail both important spatial, and movement organization components.Almost a century ago, R.S. Woodworth (1899) demonstrated that right hand target aiming movements were more precise than left hand movements unless the movements were made very slowly. A right hand advantage for either accuracy or movement time has been demonstrated repeatedly over the ensuing years (Annett, Annett, Hudson, & Turner, 1979; Bradshaw, Bradshaw, & Nettleton, 1988; Carson, Chua, Elliott, & Goodman, 1990; Fisk & Goodale, 1985; Flowers, 1975; Honda, 1982; MacKenzie, Sivak, & Elliott, 1988; Roy, 1983; Roy & Elliott, 1986, 1989; Todor & Cisnesos, 1985; Todor & Doane, 1978). (f.1) While it has been suggested that the right hand system is superior at processing movement related feedback (Flowers, 1975; Todor & Cisnesos, 1985), Roy and Elliott (1986, 1989) have shown that manual aiming asymmetries do not depend on the availability of visual information about limb and target during the actual movement (see also Carson, Chua, Elliott & Goodman, 1990; Woodworth, 1899). This finding prompted Roy and Elliott (1989) to propose that right hand advantages at aiming/reaching result from a left hemisphere superiority at timing the forces required to accelerate and decelerate the movement. This type of explanation not only appears to reconcile the findings from aiming studies, but is also compatible with suggestions about the mechanisms underlying right hand advantages in rapid finger - tapping (Peters, 1980), finger sequencing (Todor & Smiley, 1985) and throwing (Peters, 1990; see also Watson & Kimura, 1989). …