There are two specific aims to this proposal: a) To document and understand the interaction between the control of sitting posture and the coordinated actions of hands, upperlimbs and trunk involved in reaching by 6-month-old infants, either able or yet unable to sit on their own (experiments 1 & 2), and b) To document and understand young infant's detection and use of external body support to perform a purposive act, i.e. to reach, grasp and retrieve an object placed at various distances for manipulation and oral exploration (experiments 3 & 4). A) Experiment 1 is an attempt to replicate and substantiate pilot observations suggesting that coordinated trunk and upperlimbs is an emergent property controlled by the relative amount of external body support provided to 6-month-old non-sitter infants. This first study is aimed at demonstrating that under good support conditions, non-sitter infants resemble sitter infants of the same age. Experiment 2 is aimed at documenting two basic components of trunk participation in early reaching, ie.e. trunk rotation and forward leaning. Expression of these two components of trunk participation will be considered in non-sitter and sitter 6-month-old infants relative to various conditions of external body support and constraint. B) Experiment 3 is aimed at documenting the impact of postural support provided to sitter and non-sitter 6-month-old infants on the extent of their perceived prehensile space. In various conditions of postural support, these infants' trunk and upperlimb distances. Experiment 4 is aimed at studying the impact of postural support on the expression """"""""oral capture"""""""" in 6-month-old sitter and non-sitter infants. Oral capture is the phenomenon discovered in pilot observations, where infants who have their hands constrained to their sides lean forward with the trunk to contact an object with the mouth.
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