Integration process of visual and haptic information based on experiments about size perception of solid objects

When humans recognize external information, multiple kinds of sensory information are integrated and recognized in most cases. When a solid object is to be recognized, for example, not only visual information, but also somato-sensory information and motor information obtained by actually grasping the object previously, are integrated for recognition, To investigate such integration processes for various kinds of sensory information in the brain, we performed some psychophysical experiments on the information processing involved in size perception of solid objects. First, an experiment on the estimation of object size by active finger movement and an experiment on the estimation of object size by passive finger movement were performed. The latter experiment revealed that even if the object size was the same, there was a large difference in the estimation of the object depending on the initial position at the start of estimation. It was also found that the difference in estimation was reduced if an opening-and-closing finger movement is performed immediately before estimation. Additional experiments were performed in order to investigate the factors that produce estimation difference from the viewpoint of the information transformation process. The results suggest that the difference originates from the module that calculates the inverse kinematics in order to compute the finger joint angle from the perceived size of the object. It is believed that the difference originates from redundancy in inverse kinematics. © 2004 Wiley Periodicals, Inc.