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Visuomotor coordination in infancy: Reaching for a moving object under different conditions of occlusion
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VISUOMOTOR COORDINATION IN INFANCY: REACHING FOR A MOVING OBJECT UNDER DIFFERENT CONDITIONS OF OCCLUSION Daniel J. Robin University of Massachusetts, Amherst From the very onset of reaching at 4 to 5 months of age, infants can reach for and contact both sounding and glowing objects in the dark (Clifton, R., Muir, D., Ashmead, D., & Clarkson, M., 1993). By 5 months of age infants can intercept a moving glowing object in the dark as efficiently and accurately as they can intercept a moving object in the light (Robin, Clifton, & Berthier, in press). Infants’ success at these tasks shows that sight of the target in conjunction with proprioceptive feedback is sufficient to allow for proficient reaching as early as 5 months of age, and that sight of the reaching hand is not required. Infants thus have an early intermodal coordination between visual and proprioceptive input. The task in the present study demands more than coordination between sight of the target and proprioceptive feedback by introducing significant interference with the visibility and accessibility of the target. 7.5 month old infants were presented with a target object that moved laterally back and forth in front of them three times at 25 cm/set in the light and in the dark (with an illuminated object). The object passed within reaching space, at the infants’ midline, for approximately 1.5 seconds. In onehalf of the trials the object was visually obscured for a full second prior to arriving within reaching space by either moving behind a screen or, in a darkened room, by the object’s illumination blinking off. The infants’ success under these difficult conditions (51% of trials in the light, 58% of trials in the dark) shows that they can compensate for a major loss of sight of the target object. Many of their failures resulted from crashing into the screen in the light (58% of light misses) or stopping their reach when the object “disappeared” in the dark (34% of dark misses). This suggests that their motor planning regarding aiming and timing was even more accurate than success rates suggest, but actual contact was hindered by other factors such as failure to account for obstacles in their reaching path in the light and surprise in the dark. Infants often initiated a reach while the target was obscured or continued a reach toward the point of contact after the object disappeared from sight. These actions suggest that infants can use speed and path information about a target object in the visual absence of the object, and can perform a prospective action based on previously viewed target information. The infants do not require “on-line” continuous visual feedback regarding target speed, path, or position. Observation of the infants’ looking behavior showed that they looked to the location of the object’s reappearance before the arrival of the object. This behavior, in conjunction with the reaching behavior, suggests that the infants anticipated the reappearance of the object. Overall, their behavior constitutes a relatively complex example of a future-oriented behavior that utilized intermodal coordination and nmsnmtivn
actinn
VISUOMOTOR COORDINATION IN INFANCY: REACHING FOR A MOVING OBJECT UNDER DIFFERENT CONDITIONS OF OCCLUSION Daniel J. Robin University of Massachusetts, Amherst From the very onset of reaching at 4 to 5 months of age, infants can reach for and contact both sounding and glowing objects in the dark (Clifton, R., Muir, D., Ashmead, D., & Clarkson, M., 1993). By 5 months of age infants can intercept a moving glowing object in the dark as efficiently and accurately as they can intercept a moving object in the light (Robin, Clifton, & Berthier, in press). Infants’ success at these tasks shows that sight of the target in conjunction with proprioceptive feedback is sufficient to allow for proficient reaching as early as 5 months of age, and that sight of the reaching hand is not required. Infants thus have an early intermodal coordination between visual and proprioceptive input. The task in the present study demands more than coordination between sight of the target and proprioceptive feedback by introducing significant interference with the visibility and accessibility of the target. 7.5 month old infants were presented with a target object that moved laterally back and forth in front of them three times at 25 cm/set in the light and in the dark (with an illuminated object). The object passed within reaching space, at the infants’ midline, for approximately 1.5 seconds. In onehalf of the trials the object was visually obscured for a full second prior to arriving within reaching space by either moving behind a screen or, in a darkened room, by the object’s illumination blinking off. The infants’ success under these difficult conditions (51% of trials in the light, 58% of trials in the dark) shows that they can compensate for a major loss of sight of the target object. Many of their failures resulted from crashing into the screen in the light (58% of light misses) or stopping their reach when the object “disappeared” in the dark (34% of dark misses). This suggests that their motor planning regarding aiming and timing was even more accurate than success rates suggest, but actual contact was hindered by other factors such as failure to account for obstacles in their reaching path in the light and surprise in the dark. Infants often initiated a reach while the target was obscured or continued a reach toward the point of contact after the object disappeared from sight. These actions suggest that infants can use speed and path information about a target object in the visual absence of the object, and can perform a prospective action based on previously viewed target information. The infants do not require “on-line” continuous visual feedback regarding target speed, path, or position. Observation of the infants’ looking behavior showed that they looked to the location of the object’s reappearance before the arrival of the object. This behavior, in conjunction with the reaching behavior, suggests that the infants anticipated the reappearance of the object. Overall, their behavior constitutes a relatively complex example of a future-oriented behavior that utilized intermodal coordination and nmsnmtivn
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