By touching the slide with her fingertips, this child is using tactile flow
An international research collaboration between York University Faculty of Health Professor Laurence Harris and researchers in Japan has discovered that our perception of self motion has a previously unknown safety feature.
Their discovery involves tactile flow, the tactile stimulation provided as you push through leaves in the undergrowth or rub your hands along a wall, and its predominant role in enhancing our sense of self-motion, overriding the information provided by vision and the balance-and-movement system contained within the inner ear.
"When you move around you have visual information that tells you how you’re moving and when you walk around the information flows past you," says Harris. “If you’re touching something stationary as you move, such as a wall or the banisters then that information, that tactile information, will also flow over your skin."
Harris, who is the director of the Centre for Vision Research at York University, was invited to the Tohoku Gakuin University (TKU) in Sendai, Japan. There he collaborated with TKU Professor Kenzo Sakurai and researcher William Beaudot. "It was very unexpected," says Harris. "Instead of simply combining with other sensory information about the movement in the same way as for example visual and acceleration cues combine, tactile flow actually dominated perceived self-motion."
From left: William Beaudot, Laurence Harris and Kenzo Sakurai
The addition of tactile information seems to provide a sort of emergency override, says Harris, making people feel they are going faster than they really are – something he says that may contribute to the "thrill of sliding down the banisters."
In their experiments, the researchers measured the perception of self-motion; how fast a person was going and how the perceived timing of the motion was impacted by the addition of tactile flow. Harris adds that there are special receptors in the skin that are specialized to respond to something moving over the skin.
"We had people sitting on a swing that could move from side to side. Participants rested their fingertips on a flat piece of wood that was stationary. As they moved from side to side, they could feel the motion on their fingertips," says Harris. "We discovered that this made them feel they were moving faster than when they were not feeling the tactile flow at the same time."
The importance of this newly discovered role of touch in our sense of self-motion may account for why we reach for something to stabilize ourselves to prevent a fall if we miss a step. Holding on to something provides stability and provides a tactile cue about what is happening, overriding other available cues. The discovery also has ramifications for virtual reality and for airline pilots.
"Artificial tactile stimulation might be a powerful aid to provide self-motion information in virtual environments or in situations where accurate knowledge about self-motion is critical, such as when flying a high-performance plane," says Harris. "In people who are at risk of balance problems, such as older or blind individuals, or people who have had damage to the vestibular system, this information could provide an additional motion cue for them to help create tools for them."
The researchers used TKU’s parallel swing, a specialized apparatus that moves a person from side to side. In their study, they had test subjects swing with and without tactile clues (created by running fingertips along a stationary surface).
The research Tactile flow overrides other cues to self-motion is published in the journal Scientific Reports and appears on nature.com.