The influence of size perception and internal modeling on the control process while lifting

The present study sought to verify object size perception through internal modeling while lifting an object. Electromyography (EMG) activity of the upper limb muscles was recorded while 20 healthy females alternately lifted two containers of the same weight, but were unequal in size. When subjects lifted the small container, a significant increase was observed in the EMG activity. Most subjects determined that the small container was heavier than the large container, and predicted that the large container would be heavier than the small container due to size difference. The results may be explained by supporting that subjects predict object weight based on perception of size through internal modeling; however, predictions are cross-checked and modified through sensory feedback based on subjective weight.