This study presents a method to quantify a child's sensitivity to passive limb motion, which is an important aspect of kinaesthesia not easily examined clinically. Psychophysical detection thresholds to passive forearm motion were determined in a group of 20 typically developing pre-adolescent children (mean age 12y 6mo, SD 10mo, range 11-13y) and a group of 10 healthy adults (mean age 29y 10mo, SD 10y 7mo, range 18-50y). A newly designed passive motion apparatus was used to measure the time to detection of forearm motion and the errors in determining movement direction. Results showed that limb motion sensitivity became increasingly variable below 0.3 degrees /s in children and adults. In comparison with adults, movement detection times in the pediatric group were increased by between 4% and 108% for the range of tested velocities (0.075-1.35 degrees /s). At 0.075 degrees /s, 5% of the children, but 50% of the adults, made no directional error, indicating that motion perception became unreliable at such low velocity in both groups. The findings demonstrate that sensitivity to passive forearm motion in children should be tested at a range between 0.075 and 0.3 degrees /s. They further suggest that passive motion sensitivity may not be fully developed in pre-adolescent children.
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