My paper for IROS 2014 discusses human fingertip usage during precision manipulation. Specifically, participants manipulated a small spherical object with 2 or 3 fingertips (thumb and index or thumb, index, and middle fingers). Participants explored their workspace, and the resulting object and fingertip locations were recorded using a magnetic tracker. The results show quite substantial use of the middle finger on its side surface in the 3-finger case, as well as a shift in usage of the index finger. The index finger is used more on its lateral surface in the two finger case than in the three finger case.
Overall, the results suggest that finger side surfaces could be useful for robotic manipulators designed for precision manipulation. It is interesting that the middle finger is used in a direction that it can’t directly actively apply force, rather the passive stiffness of the finger is often used to support the object during manipulation.
The paper can be seen here.