Video ProfilesResearch
October 2022 Issue
Perceiving the world through tactile perception
Human tactile perception
Hiroyuki Kajimoto
Professor, Graduate School of Informatics and Engineering
Hiroyuki Kajimoto is conducting research on human tactile perception, that is, how people perceive tactile sensation, why the illusion phenomenon occurs, and how to use tactile sensation for virtual reality (VR) applications.
“We are currently experiencing serious consequences related to COVID-19 and other issues,” says Kajimoto. “Over the past two years many people were not able to go to school or their office. We have realized that our freedom to move is fragile and that can be taken away suddenly. On the other hand, we have discovered that information technology, such as online conferencing, is a powerful tool for overcoming restrictions on movement. But I believe that there is still something missing from conventional technologies, specially, the sense of touch. So, in my laboratory we are conducting research on how to artificially produce a realistic sense of touch, for the VR and meta-verse world.”
Perceiving the world through tactile perception
In this research, the first major research topic is to clarify how people perceive the world through tactile perception, for example, to observe physical phenomenon, and elucidate the phenomenon of tactile illusions.
Kajimoto explains that when we touch an object, our skin makes contact with it and it is clear how the skin deforms under such circumstances. But it is difficult to observe deformation of the skin using a camera because the actual object has a rough surface. Kajimoto and colleagues developed a method in which the finger and objects being touched were all submerged in oil to make them optically transparent to enable the first ever successful observation of the deformation of a finger in contact with an object.
The sense of touch encompasses many illusory phenomena. For example, when two hands continue touch each other, it feels as though that there is a thin plate in between the hands. This illusion indicates that human perception of ‘flatness’ is ambiguous. Kajimoto hypothesized that this phenomenon is caused by symmetrical deformation of fingers and verified his hypothesis through experiments.
“Some tactile illusions produce a sense of force,” explains Kajimoto. “We have named one of the most powerful of such forces as the ‘hanger reflex’ referring to the case when a hanger is placed on the head, and the head rotates to the left or right. This phenomenon indicates that cutaneous sensation can be misinterpreted as a force sensation, and we move according to the illusory force. We have identified the locations involved in this phenomenon and confirmed that a similar illusion can be produced by something as simple as a rubber band.”
Presenting realistic tactile sensations for virtual reality and remote communications
The second research topic being explored by Kajimoto is "how to present tactile sensations to people”, for virtual reality and remote communication applications.
The most compact method of presenting tactile sensations is by electrical stimulation, where stimulating nerves inside the skin enables the presentation of distinct tactile sensations. “We have realized a tactile presentation device with more than 1,500 stimulation points, transparent electrodes on a smartphone, and high-density tactile display for fingertips,” says Kajimoto. “We are also developing new methods of tactile presentation. For example, force sensation is produced by electrical stimulation of the skin, cold temperature sensation is produced by electrical stimulation, we have designed a new vibration transducer, and temperature sensation was produced using chemical substances.”
An example of a successful link between the study of illusion and its application is the study of the hanger reflex. Research on the hanger reflex was initially conducted on the head, but it is now clear that the same phenomenon occurs in other parts of the body, such as the waist. Kajimoto and colleagues have this phenomenon to induce movement when walking or riding a vehicle such as a Segway.
In most cases, tactile sensation is presented to the fingertips for VR applications. However, Kajimoto has presented tactile sensation to the forearm or to the face with the goal to create a tactile device that can be worn more easily and still have a certain realistic and immersive feeling.
This research is an attempt to utilize a classically known illusion called kinesthetic illusion. It is known that vibration of tendons and muscles creates the illusion that the arm is moving. By utilizing this phenomenon, it is possible to present the sensation that the body is tilting, or the weight of a stick is changing in VR environments.
“My laboratory conducts research in science, engineering, and applications, mainly in tactile sensation. We are actively accepting students from overseas, so please consider joining us.”
References and further information

1. Jianyao Zhang, Hiroyuki Kajimoto, Approaches for Reproducing the Haptic Sensation of Sandpaper with Different Roughness During Bare Fingertip Interaction, Frontiers in Virtual Reality 3/ 1, 2673-4192 (2022).
2. Taha Moriyama, Hiroyuki Kajimoto, Wearable Haptic Device Presenting Sensations of Fingertips to the Forearm, IEEE Transaction on Haptics 15/ 1, 91-96, (2021).
3. Taha Moriyama, Hiroyuki Kajimoto, HARVEST: High-Resolution Haptic Vest and Fingertip Sensing Glove That Transfers Tactile Sensation of Fingers to the Back Joint, Applied Science, 11/ 1298, (2021).
Website
https://kaji-lab.jp/ja/index.php