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Visual control of precise movements must be learned in childhood. Successful development in this domain renders behaviour flexible and acutely responsive to our complex and ever-changing environment. To uncover the general principles by which this development typically occurs, we examine visually-guided stepping in mid-childhood (i) in a single step, using reaching as a comparison (ii) during walking sequences. We use motion capture and virtual reality technologies.
Expt 1. Visually-guided reaching shows a non-linear developmental trend with a period of sensory reorganisation in mid childhood associated with a temporary decline in performance (Bard et al, 1990; Hay et al, 1991; Van Braeckel et al, 2007). But, does sensory reorganisation have a parallel impact on visually-guided stepping? We tested 6, 7 and 8 year old children (right hand and foot dominant) on an upper-limb reaching task and a parallel precision stepping task. An adult sample completed the stepping task only. Participants reached their hand/foot toward targets both straight ahead and to the side. Distance to target was scaled to leg length and arm length. We occluded visual input at movement onset on 50% of trials and recorded movement error using motion capture. Since stepping carries additional balance demands, we measured postural stability with and without visual input, to determine whether developmental improvements in stepping might be a product of improving postural control. From 6 years of age, children used vision to reduce error for both reaching and stepping. For stepping, error was adult-like by 8 years of age, despite postural stability remaining immature. We, therefore demonstrate significant developmental improvements in stepping accuracy, which were not solely a product of improving postural control. Further, stepping accuracy improved gradually and linearly, whilst reaching accuracy showed no change between 6 and 8 years. Visually-guided reaching and stepping therefore have different developmental profiles. From these results, we argue for a prolonged period in the development of visually-guided stepping, and for the limb-specificity of developing motor control.
Expt 2. Having demonstrated that even young children use vision to optimise the accuracy of single steps, we next explore children’s use of vision to guide foot placement during walking. When walking in complex environments, adults visually sample from ahead to plan foot placement (Matthis et al, 2018). Do children also engage in feedforward visual sampling during walking, and does their visual strategy during walking sequences relate to their use of vision for single steps? In fully immersive virtual reality, participants walk across a series stepping stone targets. With stepping distances scaled to leg length, we manipulate the number of visible upcoming steps to 1, 2 or 3 steps ahead. Participants also complete a virtual single-step task as in Expt 1. We use motion capture to record stepping speed and error. Participants’ performance on the single step and the walking precision tasks will be compared. We will present early findings from this experiment, which is currently underway. Together these experiments give a new window onto the use of vision in everyday whole-body motor tasks during the mid-childhood years.