When humans sense the hardness of real objects, their perception is known to be influenced by not only tactile information but also visual information. In a mixed-reality (MR) environment, the appearance of touchable objects can be changed by superimposing a computer-generated image onto them (MR visual stimulation). In our previous study, we first superimposed computer-generated images (CGI) on real objects, and then, applied extreme deformation to the superimposed images while the participants pressed the real objects with their fingers. The results showed that humans sense hardness differently while receiving MR visual stimulation; we named this psychophysical effect the dent-softness illusion. As the next step, in this study, we verify whether humans perceive hardness differently when pressing a real object with and without superimposed animation and whether the dent-softness illusion occurs in different parts of the body such as the finger, palm, and arm.

In a mixed-reality (MR) environment, the appearance of touchable objects can be changed by superimposing a computer-generated image (CGI) onto them (MR visual stimulation). At the same time, when humans sense the hardness of real objects, it is known that their perception is influenced not only by tactile information but also by visual information. In this paper, we studied the psychophysical influence on the sense of hardness by using a real object that has a CGI superimposed on it. In this experiment, we deform in an extreme way the CGI animation on the real object, while the subject pushes the real object using his/her finger. The results of the experiments found that human subjects sensed different hardnesses by emphasizing the dent deformation of the CGI animation.