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Erin Babinsky, Oliver Braddick, Janette Atkinson; What visual information can infants use for reaching in the dark?. Journal of Vision 2009;9(8):1157. doi: 10.1167/9.8.1157.
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The information available for visual control of a reaching action differs between (a) a fully lit environment; (b) a visible target object in an otherwise dark environment; (c) occlusion by darkness of a previously visible object. In (c), Westwood and Goodale (2003) argue that the dorsal stream information, normally used to guide action, decays rapidly and that a ventral stream representation has to be substituted. We have examined the developmental role of visual subsystems in reaching control, by using an infrared motion tracking system to measure the kinematics of reaches by 9, 13, and 16 month infants (N=28) compared to adults in these three conditions. Unlike most earlier studies of reaching in the dark, we concentrate on the characteristics of the transport phase (duration, straightness, period of deceleration) rather than the final grasping action.
We find that, unlike adults', 9 month olds' reaching becomes less controlled and more ballistic in the dark and does not usually terminate in a controlled grasp. Older infants appear to be making more use of a continuing visual representation of the invisible target object although the penalty in accuracy and speed is greater than for adults, and they do not show an increasing penalty with increasing delay.
For a glowing target object in a dark environment, 13 month olds' reach duration shows a greater difference from full illumination than either younger infants or adults. We will discuss whether this anomalous behaviour results from absence of information from the hand or from the environmental context, and more broadly whether there is any evidence for a ventral stream representation that infants can access for reaching control.
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