The effects of vision and weight on digit placement during reach to grasp a glass of water

Abstract

Previous many researches have confirmed that human adapt the position of digits to object attribute, for example, the shape of objects and center of mass (COM). Eight healthy subjects took part in the experiment (four females and four males, aged between 20 and 25 years), and they were righthanded. The goal of this research was to confirm the influence of object's vision and weight on digit placement during reach-to-grasp a glass of water. Subjects placed their digits on a glass when the type (transparent and opaque) and capacity (200 ml and 400 ml liquid) of the glass were altered. Our results showed that subjects varied digit placement according to vision and weight when grasping the glass for movement. Weight affected digit placement: under vision condition, all the digits were located relatively higher in vertical placement and were wrapped more around the glass with the increase of weight, expect the little finger; under non-vision condition, only the index finger had a significant difference with the change of weight. At the same time, in order to find the difference between the fingers position, we examined the vertical distance between the thumb and other fingers. We found which the relative digit placement was affected by vision and weight. These findings extend the previous studies showing that the digit placement is not only affected by weight but also vision factor during grasping movements.