Visual illusions and the control of children arm movements

The aim of the present study was to determine whether children like adults (Gentilucci M, Chieffi S, Daprati E, Saetti MC, Toni I. Visual illusion and action. Neuropsychologia 1996;34:369-76; Gentilucci M, Daprati E, Gangitan o M, Toni I, Eye position tunes the contribution of allocentric and egocent ric information to target localisation in human goal directed arm movements . Neurosci Lett 1997:222:123-6) are influenced by visual illusions when the y transform visual information in motor command. Children and adults pointe d to a shaft extremity of the Muller-Lyer configurations, as well as to an extremity of a control configuration. Movements were executed in two experi mental conditions. In the vision condition subjects saw both the stimulus a nd their hand before and during movement. In the no vision (memory) conditi on subjects saw the stimulus and their hand before, but not during movement . Movement started 5 s after vision was precluded. The Muller-Lyer illusion affected pointing kinematics of both children and adults. As found previou sly (Gentilucci M, Chieffi S, Daprati E, Saetti MC, Toni I. Visual illusion and action. Neuropsychologia 1996,34:369-76; Gentilucci M, Daprati E, Gang itano M, Toni I. Eye position tunes the contribution of allocentric and ego centric information to target localisation in human goal directed arm movem ents. Neurosci Lett 1997;222:123-6), subjects undershot and overshot the sh aft extremity of the closed and of the open configuration, respectively. Th e illusion effect was greater in the no vision than in the vision condition . These results show that in children like in adults the system underlying visual perception in an object-centered frame of reference and that involve d in motor control functionally interact with each other. Although the proc esses of target localisation were the same, the transformation of target po sition information in a sequence of motor patterns was different in childre n from that in adults. Even if both children and adults lengthened duration of the deceleration phase in the vision condition, only adults shortened d uration of the acceleration phase in order to maintain constant movement ti me (Viviani P, Schneider R. A developmental study of the relationship betwe en geometry and kinematics in drawing movements. J Exp psychol 1991;17:198- 218). This result suggests that children an yet unable to co-ordinate tempo rally acceleration with deceleration phase. (C) 2000 Elsevier Science Ltd. All rights reserved.