The human sense of touch is more acute than previously realized, say Swedish scientists who conducted first-ever measurements of human tactile perception. Experiments at the KTH Royal Institute of Technology in Stockholm have shown people can detect wrinkles at the nano-scale while running their fingers over a seemingly smooth surface, they reported. The human finger can discriminate between surfaces patterned with ridges as small as 13 nanometers in amplitude and non-patterned surfaces, surface chemistry Professor Mark Rutland said. \"This means that, if your finger was the size of the Earth, you could feel the difference between houses [and] cars,\" Rutland said. \"That is one of the most enjoyable aspects of this research. We discovered that a human being can feel a bump corresponding to the size of a very large molecule.\" The findings could lead to such advances as touch screens for the visually impaired and other products, the researchers said. \"The important thing is that touch was previously the unknown sense,\" Rutland said. \"To make the analogy with vision, it is as if we have just revealed how we perceive color.\"