Effects of contextual constraints on reaching performance in adults without disabilities: A kinematic study

Contextual constraints play an important role in determining motor behavior of any individual. Three major sources of constraints to action include the environment, organism, and task. This study was conducted to examine the effects of task constraints on reaching kinematics in adults without disabilities. Task constraints were varied by changing the functional level of task goal and functional specificity of target object. A drinking activity under four experimental conditions formed by the crossing of functional goal and object affordances was performed by 24 healthy young adults. Under the higher level of a functional goal, participants were asked to take a drink from a can of cola. The lower level of a functional goal involved bringing a can of cola to the mouth. The level of object affordances depended on whether a commercial label on the can was present (i.e., the enriched condition) or occluded (i.e., the impoverished condition). Results indicated that a higher functional goal with enriched affordances elicited significantly more efficient movements (i,e., shorter movement time and higher average velocity) than the condition of a higher functional goal with impoverished affordances that in turn produced faster movements than the condition of a lower functional goal with enriched affordances. Reaching for a lower functional goal with impoverished affordances elicited the least efficient movements among the four conditions. The findings lent some support for the modifiability of reaching kinematics through varying the task constraints and afforded implications for occupational therapy. Further research may explore therapeutic possibilities for training patients with neurological impairments to accomplish functional tasks more efficiently by affording enriched contexts. Directions for such research were discussed.