The kinematics of eating with a spoon: bringing the food to the mouth, or the mouth to the food?
In traditional reach-to-point and reach-to-grasp studies an increase in accuracy demands typically results in a lengthening of the deceleration phase of the reach and a freezing of the more distal joints. The purpose of the present experiment was to examine whether similar changes in the reach kinematics could be observed during a tool-using skill, as would be predicted from an effector independence perspective. Five subjects were required to eat two substances (i.e. a solid and a liquid one) that imposed different requirements on the accuracy of the movement. The subjects transported the substances from the plate into the mouth. A prolonged movement duration was found for the liquid as compared to the solid substance. However, rather than being exclusively due to a lengthening of deceleration phase, the larger movement duration resulted from a slowing down of the whole movement. Therefore, the skewed velocity profiles found in the traditional reach-to-grasp studies may well be the result of the accuracy demands only impinging on the final part of the movement trajectory, rather than being a consequence of central, effector-independent, organising principles. In addition, under increased accuracy demands subjects were shown to redistribute their movement in a proximodistal direction. Movements of the distal components were reduced to a minimum and the involvement of trunk and head movement increased.
van der Kamp
J
J
Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands. J_van_der_Kamp@fbw.vu.nl
Steenbergen
B
B
D000328:Adult; D001132:Arm / Q000502:physiology; D001696:Biomechanical Phenomena; D004435:Eating / Q000502:physiology*; D005260:Female; D006801:Humans; D007596:Joints / Q000502:physiology; D008297:Male; D009068:Movement / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D013997:Time Factors