touch a force for stabilityWhen people are unsteady, their minds and bodies work to stabilize them through sensory input from the inner ear, the eyes, and more. A new study from the University of Birmingham finds that there is another factor in stabilization: touch. When an individual is unsteady and receives a touch—even a light touch of fingertips—from another, the individual automatically becomes steadier. The findings are a step towards understanding how neural and mechanical processes synchronize people with those around them.

For the study, the researchers asked pairs of participants to stand on force platforms. While the platforms jostled participants, the researchers conducted tests. To determine how individuals incorporate visual and mechanical interactions, the participants used several combinations of touch and vision. In each test, the pairs engaged in physical contact: lightly touching each other, grasping shoulders, or not touching at all. At each level of physical contact, the participants also combined a visual element. In each test, the pars varied their visual input. They tried combinations of both people closing their eyes, both opening their eyes, or one person with eyes closed and the other with eyes open.

Not surprisingly, when the pairs grasped shoulders, their sway was 37 percent lower than with no contact. Interestingly, the pairs swayed 18 percent less when engaged only in a gentle fingertip touch. This suggests that light touches act as a “sensory weighting phenomenon.” When the brain estimates how upright the body is, it uses a weighted combination of sensory feedback. The study shows that the body can also account for the motion of another person when estimating uprightness.

The researchers found that this same phenomenon manifests even when people cannot see. When a participant with closed eyes lightly touched her partner, the partner’s motion steadied. This indicates that an individual can receive a stabilizing benefit from touch, even when the person offering the touch may be less stable.

Understanding how touch impacts sensorimotor calculations could help researchers develop smarter walking devices or more effective rehabilitation techniques. The findings could also factor into interventions for people with sensorimotor deficits.

“There’s something very human, very instinctive, that makes us reach out and grab something or someone when we’re unsure of our balance and experience sway. We know this. But being able to significantly reduce that sway with even the gentlest touch tells us a lot about how out body relates to the people around us,” concluded study author Dr. Raymond Reynolds.

This research is published in the journal Interface.

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