  To touch and be touched are vital to human development, well being, and
relationships. However, to those who have lost their arms and hands due to
accident or war, touching becomes a serious concern that often leads to
psychosocial issues and social stigma. In this paper, we demonstrate that the
touch from a warm and soft rubber hand can be perceived by another person as if
the touch were coming from a human hand. We describe a three step process
toward this goal. First, we made participants select artificial skin samples
according to their preferred warmth and softness characteristics. At room
temperature, the preferred warmth was found to be 28.4 deg C at the skin
surface of a soft silicone rubber material that has a Shore durometer value of
30 at the OO scale. Second, we developed a process to create a rubber hand
replica of a human hand. To compare the skin softness of a human hand and
artificial hands, a robotic indenter was employed to produce a softness map by
recording the displacement data when constant indentation force of 1 N was
applied to 780 data points on the palmar side of the hand. Results showed that
an artificial hand with skeletal structure is as soft as a human hand. Lastly,
the participants arms were touched with human and artificial hands, but they
were prevented to see the hand that touched them. Receiver operating
characteristic curve analysis suggests that a warm and soft artificial hand can
create an illusion that the touch is from a human hand. These findings open the
possibilities for prosthetic and robotic hands that are lifelike and are more
socially acceptable.
