In general, seismic waves are related to earthquakes and have been utilized by researchers to create a universal scaling law for the sense of touch.
A research team under the guidance of scientists from the University of Birmingham used Rayleigh waves to develop the first-ever scaling law for touch sensitivity.
The study results were published in the Science Advances journal.
The team forms part of a European consortium (H-Reality) that is already making use of the theory to create new virtual reality technologies including the sense of touch.
Rayleigh waves form when objects collide with one another and are generally believed to travel only along surfaces. The researchers found that in the case of touch, the waves also travel via layers of skin and bone and are gathered by the touch receptor cells of the body.
The researchers used mathematical modeling of the touch receptors and demonstrated how the receptors were situated at depths that enabled them to react to Rayleigh waves. Although the interaction of these receptors with the Rayleigh waves differs based on species the ratio of receptor depth versus the wavelength continues to be the same, thus allowing the universal law to be defined.
The mathematics utilized by the team to develop the law depends on methods that were initially developed more than a hundred years ago for earthquake modeling. The law backs predictions by Georg von Békésy, the Nobel-Prize-winning physicist who first reported that the mathematics of earthquakes could be useful to examine the connections between Rayleigh and waves touch.
Moreover, the researchers identified that the interaction of the receptors and waves continued to be the same even if there is a change in the hardness of the outermost layer of skin. The potential of the receptors to react to Rayleigh waves stayed unaltered despite the several changes in this outer layer caused by profession, gender, age, or even hydration.
According to Dr Tom Montenegro-Johnson of the University of Birmingham’s School of Mathematics, who led the study, “Touch is a primordial sense, as important to our ancient ancestors as it is to modern day mammals, but it’s also one of the most complex and therefore least understood. While we have universal laws to explain sight and hearing, for example, this is the first time that we’ve been able to explain touch in this way.”
The principles we’ve defined enable us to better understand the different experiences of touch among a wide range of species. For example, if you indent the skin of a rhinoceros by 5mm, they would have the same sensation as a human with a similar indentation—it’s just that the forces required to produce the indentation would be different. This makes a lot of sense in evolutionary terms, since it’s connected to relative danger and potential damage.
James Andrews, Study Co-Author, University of Birmingham
The study was financially supported by the European Union’s Horizon 2020 research and innovation program, under the collaborative project “H-Reality” (grant 801413, hreality.eu). The other institutions that took part in the project are Ultraleap Ltd. (UK), CNRS (France), TU Delft (The Netherlands), and Actronika (France).
Andrews, J. W., et al. (2020) A universal scaling law of mammalian touch. Science Advances. doi.org/10.1126/sciadv.abb6912.