Force is more important than form when it comes to touch, show brain researchers in this week’s Nature. 

Running fingers over an object’s surface tells us what’s underneath — from the geometry, the path taken by the fingers, and the force exerted by the object on our fingertips. An ingenious experiment designed by Gabriel Robles-De-La-Torre and Vincent Hayward of McGill University in Montreal, Canada, separates these two influences on touch or ‘haptic’ perception. Subjects moved a robotic ‘manipulandum’ over a surface and said whether they felt it pass over a bump or hole. The authors also created virtual bumps and holes by simulating the horizontal forces such a feature would exert, without the vertical movement. The force cues of a virtual bump can override geometry of a hole, they found, when the two were combined.

Three-dimensional shapes could feel real in virtual reality by using such forces, suggest Randall Flanagan and Susan Lederman in a related News and Views article. The findings could also help untangle the brain-wiring beneath touch.