Errors in kinesthetic transformations for hand apposition.

We investigated the ability of human subjects to duplicate with the left hand the spatial location of the right hand, using only kinesthetic cues. Under this experimental condition, subjects produced large and idiosyncratic errors which varied with the spatial location of the hand. Tactile cues originating from contact of the hand with a rigid surface generally led to a decrease in the variable error. However, even without tactile cues, the variable error was small compared with other tasks in which subjects are required to estimate the spatial location of the hand on the basis of kinesthetic cues. The results suggest that subjects did not derive an estimate of the location of the right hand in extrapersonal space, but rather that they performed the task within intrapersonal space.