Hello everyone. My name is Yuri Ishikawa and I work in the UX Design Department at CIC, where I mainly work as a content production planner.

I have been researching touch for the past seven years, and it is no exaggeration to say that touch is my hobby.

Our sense of touch is essential to our daily lives. From simple actions like shaking hands, hugging, and petting a pet to the vibrations of our smartphones and the feel of our clothes, touch is involved in every moment of our lives. In fact, during the COVID-19 pandemic, the reduction in physical contact has led to a chronic condition of skin hunger (a strong desire for physical communication).
There are many different fields of research in the world, but compared to vision and hearing, touch is a very exciting and interesting field packed with undiscovered phenomena and possibilities for technological expansion. Moreover, while hearing is limited to the ears and vision to the eyes, skin is found all over the body, so the research possibilities are endless.

Furthermore, when combined with other senses, touch creates richer and more meaningful experiences, making it highly compatible with entertainment.

Today I would like to talk to you about the sense of touch, and hope that it will give you a glimpse into its possibilities and appeal.

　

1. Four sensors in the skin

In fact, there are four sensors located within the skin: Meissner's corpuscles (sensors that sense low-frequency vibrations), Merkel's disks (sensors that sense shape and texture), Pacinian corpuscles (sensors that sense high-frequency vibrations), and Ruffini endings (sensors that sense skin tension). While these terms may not be familiar to most people, you can think of them as four types of sensors with different functions within the skin. Because each sensor has a different function, determining which sensor to target is important when designing haptic devices and content. These four types of sensors are called "mechanoreceptors." These sensors convert physical stimuli (mechanical energy) such as vibrations and pressure applied to the skin into electrical signals. The skin also contains sensors called free nerve endings that respond to non-mechanical stimuli (such as chemicals, pain, and temperature).

Multiple sensors with unique functions each detect tactile stimuli, and only when they are integrated can they be perceived as touch. Don't you think this process itself is mysterious and fascinating?
　　

Sensor Type	function
Meissner's corpuscles	・Detection of low frequency vibrations ・Control of grip strength Example: Gently gripping an egg
Pacinian corpuscles	・Detection of high frequency vibrations ・Detection of sensations through tools Example: The feeling of soil from a shovel in your hand
Merkel edition	-Detection of object edges, shapes, and textures Example: Jagged edges of a file
Ruffini's End	-Detection of skin tension

　　

　　

2. Tactile illusions

The great appeal of touch lies in its "illusion," which makes it possible to create a wide variety of tactile sensations even with a limited number of tactile displays (devices that present tactile stimuli).

The tactile stimulation that most of us are familiar with is probably the vibration stimulation caused by the vibrators (electronic components that generate vibrations) inside smartphones and game controllers. Even though the whole body can sense touch, it is not realistic to attach a tactile display to the whole body when releasing a product to the market. It is necessary to reproduce all the tactile sensations of the content using only the limited number of vibrators inside the housing. The same is true when using a tactile display for content experiences in space.

Below are two typical tactile illusions.

　　

Rabbit Illusion (Skin Rabbit)

The rabbit illusion is an optical illusion that makes you feel as if you are being touched repeatedly in areas that are not actually being stimulated.

For example, if you have your eyes closed and are tapped quickly at two points on the skin of your arm, you will feel a series of "tap tap" sounds in the area between the two points (between points A and B in the diagram below), even though they are not actually being tapped. This phenomenon has come to be called the rabbit illusion, as it feels as if a rabbit is hopping around on your skin.

　　
　　

Phantom sensation (sensory funnel phenomenon) 

Phantom sensation (sensory funnel phenomenon) is an illusion in which, when multiple tactile stimuli are presented simultaneously, the sensation is felt at an intermediate point that is not actually stimulated.

For example, if you hit two points on your arm at the same time, it will feel like the hit is in the middle (left image below). Also, if you hit one side with more force, it will feel like the hit is in a position slightly closer to the stronger point (right image below).

This phenomenon, in which multiple stimuli are perceived as coming together in the center, is called the sensory funnel phenomenon. The name comes from the fact that when liquid is dropped on the edge, it flows down the funnel and gathers in the center. This phenomenon is also widely used in the field of tactile engineering, where it is known as phantom sensation.

　　
The common feature of these two illusions is that the user perceives a tactile stimulus to be presented in a location where no tactile stimulus is presented. By utilizing these illusions, it is possible to increase the degree of freedom in tactile expression, and it is possible to present vibration stimuli in various locations using multiple vibrators inside the housing, which is a challenge for haptic devices.

In addition to the illusions mentioned above, there are various other illusions, such as the illusion of apparent motion, which makes it seem as if a tactile stimulus is moving continuously from left to right or right to left. Research is also underway to show that similar phenomena can occur with other tactile stimuli, such as hot and cold stimuli, in addition to vibration.

Illusions are not just mysterious phenomena, but are a powerful tool for broadening the range of tactile expression. By skillfully combining these illusions, we can design tactile sensations.

　　

3. Haptic Design (Design for the Sense of Touch)

Vibration stimulation is highly compatible with music, as the speaker itself can act as a vibrator. For example, vibration stimulation is actively used in 4D movies and theme park attractions. While haptic sensations are often incorporated into these contents as an "added-on effect," the appeal of haptic design is that they can be created simultaneously as part of the content from the beginning. By incorporating haptic sensations that match the content, such as video and music, into the design from the start, and refining the content and haptic sensations simultaneously, the range of haptic sensations can be further expanded.

In addition to vibration, tactile stimuli such as heat and cold, wind, and pressure are increasingly being incorporated into content. I spend my days hoping that in the future, we will see an increase in people who design with intention, rather than just adding tactile sensations haptically - people who could be called "haptic designers."

　　

Conclusion

I am convinced that haptic technology will broaden the scope of content experiences and help create spaces that create a "WOW" that we have never experienced before. It will not only enhance the content experience within a space, but also make VR, medical devices, and everyday interfaces richer and more engaging. We are now at the turning point where the sense of touch was just beginning to be recognized and used, and we are entering an era in which we must establish better haptic expression. I am excited to think about what kind of haptic content will be created in my lifetime and how far the technology will expand.

If you have any questions about haptics technology, please feel free to contact us at any time. Of course, we are also happy to talk about or listen to your concerns regarding the sense of touch.

　　

References

David J. Linden and Akira Iwasaka (2016). The Science of Touch, Kawade Shobo Shinsha.
・Geldard, FA, & Sherrick, CE (1972). The Cutaneous “Rabbit”: A Perceptual Illusion. Science, 178(4057), 178-179.
・Geldard, FA (1982). Saltation in somesthesis. Psychological Bulletin, 92(1),136-175.
・von Bekesy, G. (1959). Neural Funneling along the Skin and between the Inner and Outer Hair Cells of the Cochlea. The Journal of the Acoustical Society of America, 31(9), 1236-1249.
・Wieland, BA (1960). The Interaction of Space and Time in Cutaneous Perception. The American Journal of Psychology, 73(2), 248-255.
・Gardner, EP, & Spencer, WA (1972). Sensory funneling. I. Psychophysical observations of human subjects and responses of cutaneous mechanoreceptive afferents in the cat to patterned skin stimuli. Journal of Neurophysiology, 35(6), 925-953.