Abstract
The present study aims to verify the perception of object size and the internal model that influence the control process for lifting. Twenty healthy females participated in the study. Two containers of the same weight, but unequal sizes (large and small) were prepared. Two containers were lifted alternately in 5 trials. Using a surface electromyography, activities of trapezius muscle, deltoid muscle, biceps brachii muscle, and brachioradialis muscle were recorded while lifting the container and the integral values were calculated for one second from the start of lifting. After each trial, the subjects' feeling about difference in weight and their prediction of weights before lifting were described. In the first trial, when lifting the small container, a significant increase was observed in biceps brachii muscle and brachioradialis muscle in group A (starting with the large container). And when lifting the large container, a significant decrease was observed in deltoid muscle and biceps brachii muscle in group B (starting with the small container). From the second to the fifth trials: the difference got smaller with trial in both group A and group B. After the first trial, most subjects determined the small container was heavy. Also, before lifting, most subjects predicted the large container would be heavy because of the difference in size. It can be explained that those results were obtained because; 1) the subjects predicted the small container would be light from the perception of object size and internal model, but 2) the predictions were cross-checked and modified by the sensory feedback on their subjective weight.
