The impact of body-scaled information on reaching

Background. Environmental and task modifications are powerful methods used to affect action in rehabilitation and are frequently used by therapists. Objective. The purpose of this study was to examine and quantify the relationship between hand size (person characteristics) and object size (environmental characteristics) and the effect of this relationship on the emergent reaching patterns for children and adults with typical development. Design. This was a cross-sectional prospective study. Methods. Seventeen children and 20 adults participated and were required to reach and grasp 10 pairs of cubes of different sizes. The dimensionless ratios were calculated by dividing the cube size by the aperture between index finger and thumb to quantify emergent reach and grasp patterns. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach pattern. Results. The results demonstrated no significant difference in the mean critical ratios between the 2 groups. However, a 2-handed reach was used more frequently than a 1-handed reach at a significantly smaller ratio for children in comparison with adults. Limitations. The relational metrics between the cube and hand are only one contribution to the emergent reaching and grasping patterns. Conclusions. Children had more variability of reaching patterns than adults. A personal constraint, such as experience, and a task constraint of accuracy may account for the variability. The results encourage further research on body-scaled information for individuals with different personal constraints (eg, children with cerebral palsy) and the impact of body-scaled information on emergent actions.