Precise tactile localization on the human fingernail

Fingernails are specialized features of the primate hand, which are believed to contribute to manual dexterity. The sensorimotor functions of fingernails, however, remain poorly understood. This study investigates the ability of humans to precisely localize touches applied to the fingernail plate. Nine different locations on the fingernail were touched and participants judged the location by clicking a mouse cursor on a photograph of their finger. Performance in this condition was compared with stimuli applied to the skin of the fingertip. The results showed that participants are able to localize touch on the fingernails at substantially higher than chance levels. Moreover, the precision of this ability is not appreciably lower than that of the fingertips. These results show that the fingernail is a highly sensitive sensory organ, which is capable of providing rich spatial information about tactile stimuli.