Investigating phantom movements in tactile illusions

Noticing that something is moving on a portion of our skin when it is not, or, put another way, experiencing a tactile illusion of movement, is a less unusual situation than it may seem. And now scientists have investigated some of its limits.

That sensation that something moves on a sector of our skin when said movement does not exist is called “phantom movement.” The term appeared a few decades ago. However, the new study has made it possible to determine, for the first time, the minimum distance that a vibrating point must travel for this phantom movement to be perceived.

One of the authors of this research, Andrés Trujillo, professor at the Department of Electronics at the University of Malaga (UMA) in Spain, points out that the illusion of phantom movement occurs when we place two vibrating devices (known as vibrotactile actuators) at two points. other than skin. “With adequate activation, it can be achieved that, instead of perceiving two isolated vibrations, the person experiences the sensation that there is a vibrating point that moves on the line between these two devices, although this point does not really exist, it is illusory” , Explain.

According to this engineer, thanks to the experiments carried out at the UMA, it has been possible to modify the configuration parameters of the phantom movement that were used until now. “We have developed an instruction manual to know what the operating limits of this tactile illusion are,” Trujillo clarifies.

Thus, engineers from the University of Malaga have established that, on average, humans are capable of perceiving the illusion of the phantom movement of an illusory vibrating point when the distance traveled by it is at least 20 percent of the separation between actuators. .

A moment of the investigation. (Photo: University of Malaga)

Possible applications

The implementation of tactile illusions in virtual reality or augmented reality is one of its possible applications, with the main advantage that its use would allow generating sensations of movement with only a pair of actuators. “The conventional thing would be to place a series of actuators, not just two, that are systematically turned on and off to create the sensation of movement,” says Trujillo, who adds that this finding translates, therefore, into the development of lower-cost devices, lighter and with higher resolution.

Their use in vibrating vests, in video games, on touch screens for blind people or in concerts, for example, are other uses of these phantom movements, which add realism and new sensations to the perception experienced by the user.

The study is titled “Phantom sensation: Threshold and quality indicators of a tactile illusion of motion.” It has been published in the academic journal Displays. And it is the result of the doctoral thesis of researcher Paul Byron Remache-Vinueza, directed by the professor of the School of Industrial Engineering Fernando Vidal and Andrés Trujillo, and which advances the purpose of transmitting musical sensations through the skin for people with disabilities. auditory. (Source: UMA)