EFFECTS OF SURFACE TEXTURE ON WEIGHT PERCEPTION WHEN LIFTING OBJECTS WITH A PRECISION GRIP

In this paper, we show that, when lifting an object using a precision grip with the distal pads of the thumb and index finger at its sides, the perceived weight depends on the object's surface texture. The smoo ther the surface texture, the greater the perceived weight. We suggest that a smoother object is judged to be heavier because the grip force , normal to the surface, required to prevent it from slipping is great er. The possibility of there being an influence of surface texture per se is excluded by a second experiment that employed a variant of the precision grip in which the thumb supports the weight of the object fr om underneath. With the grip oriented in this way, there is no need to match grip force to surface texture and, under these conditions, ther e is no effect of surface texture on weight perception. In the first t wo experiments, the test and comparison weights were lifted successive ly by the same hand. In a third experiment, the effect of surface text ure was replicated for sequential lifts made with separate hands. Thus , the effect is not restricted to comparisons made with the same hand.