Unimanual and bimanual weight discrimination in a desktop setup

There is evidence that weight perception with one hand may be based on integrating effort signals resulting from muscular activity to support arm and weight against gravity [1]. When lifting an object with both hands, the magnitude of effort signals due to supporting the arms and weight against gravity may change in opposite ways: posture effort signals may increase due to the employment of both hands while weight effort signals may decrease due to sharing the weight between the two hands. Here, we report preliminary results of a study in which participants judged the heaviness of weights lifted with one and two hands. It was found that a weight lifted with both hands felt lighter than equal weights lifted with the left or right hand. However, unimanually lifted weights did not feel twice as heavy as bimanually lifted weights. This may suggest that an imperfect integration of both postural and weight signals could be taken into account when judging weight bimanually.