University of Malaga (UM) researchers have harnessed the ability to create ‘phantom sensations,’ or a sense of being touched, on parts of the body where there is no actual physical contact. The researchers behind the discovery also say they have determined the operating parameters and effective stimulation distances for creating phantom sensations, which could help perfect the process.
In the future, the ability to create and localize customized phantom sensations could lead to applications that assist the blind, such as “feeling” music. The team also sees potential commercial uses, including haptic vests and stimulus-response controllers that can create immersive feelings of touch when playing video games.
Two Vibrating Actuators Work Together to Create Phantom Sensations
According to the press release announcing the research, the best way to create phantom sensations is to stimulate the nerves in such a way that “a tactile illusion that does not correspond to an authentic physical stimulus.” This is done by strategically placing two vibrating actuators on the skin at a specific distance. When triggered in just the correct way, the combined activity of these actuators can create a phantom sensation on a part of the body where there is no physical contact.
“With proper stimulation, an individual, instead of perceiving two isolated vibrations, can experience the feeling that there is a vibrating point moving between these two devices; although this point does not really exist, it is illusory,” explained Andrés Trujillo, a Professor of the Department of Electronics and the lead author on the study outlining the team’s research.
While previous research has highlighted the effect of phantom sensations, their operating parameters have not been well defined. In short, researchers knew how to create a phantom sensation, but they didn’t know how far apart the vibrating actuators needed to be or exactly where to place them to create a specific, desired sensation of touch somewhere else on the body.
Setting the Parameters of Touch That Does Not Exist
To help set such parameters, which would open up potential real-world uses of phantom sensations, the team says they studied the minimum amplitude of motion at which individuals perceive a tactile illusion, each study subject’s perceived level of clarity of the phantom sensation, and how continuity of motion helped the feeling last.
According to the published study, this involved placing the two actuators on the skin a measured distance apart. If the actuators are closer than this, the phantom sensation doesn’t appear. Next, the researchers increased the intensity of the vibrations in one actuator while reducing the intensity in the other.
“We gradually increased the amplitude of motion until the participant reported perceiving the illusion,” they write in the journal Display. “This intensity variation creates the illusion of a vibrating point moving between the actuators.”
To test the duration of the sensation, the team tried various stimulation durations, ranging from one-tenth of a second to six seconds. According to their results, the study subjects felt the phantom sensation appear once the amplitude of motion was around 20%, increasing all the way up to 100%.
Notably, the clarity of the sensation was often low (described as ‘not so clear’). However, the sensation clarity increased as the vibrating actuators were tuned farther and farther apart in amplitude. The researchers also found “a positive correlation between duration and continuity of motion.” In effect, regularly moving the source vibration caused the phantom sensations to last longer.
According to Trujillo, the team’s work has not only identified a mechanism to control phantom sensations but also set the operating parameters needed to apply them in a targeted way. “We have developed an instruction manual to know the operating limits of this tactile illusion,” he said.
Applications Include VR, Gaming, and Devices for the Visually Impaired
The professor also notes that their discovery, which expands on the theory of transmitting musical sensations through the skin for people with hearing impairment, could enable the creation of a customized vest or other skin covering that contains numerous vibrating actuators placed in strategic places. When activated in a particular order or sequence, such a device could apply the team’s findings to create customized phantom sensations of different intensities, durations, and locations depending on which actuators are operating at any given time.
“The conventional application would be to place a series of actuators, not just two, and systematically switch them on and off to create the feeling of movement,” Trujillo explained.
Although the team has not progressed to the point of a commercially available product, they say that their research could offer a number of potential applications. For example, someone visiting an immersive virtual reality universe could experience the physical sensation of touch when encountering specific objects or barriers. The method could also be used in industrial or even military training scenarios, where feedback sensations can better prepare individuals working in dangerous or high-stress situations.
Also, according to the research team, “haptic vests, video games, touch screens for blind people or concerts, for example, are other applications of these phantom or apparent motion, which provides users with realism and new sensations.”
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.