Tricking the Mind: Third Arm Illusion?



CREATING THE ILLUSION: Researchers at the Karolinska Institute in Stockholm conducted an unusual experiment aimed at creating the illusion — and physical sensation — of having a third arm. While the traditional “phantom limb” experiments used mirrors to trick people into thinking a prosthetic arm was their own, this experiment put the fake one right out on the table next to the real thing. In five separate laboratory experiments, 154 volunteers were seated with their hands on a table and a rubber arm was placed next to their right arm. A sheet covered their shoulders and elbows, creating the illusion that the person had three arms. ( Source: Science Daily)

STUDY FINDINGS:   7 out of 10 participants experienced the sensation of having a third hand. The reason may be that the visual illusion creates a conflict for the brain. But instead of settling on just one arm as the real thing, the brain accepts both right hands as part of the body, causing the subjects to experience the sensation of having a third arm. To prove that the prosthetic arm was truly experienced as a third arm, the scientist 'threatened' either the prosthetic hand or the real hand with a kitchen knife, and measured the degree of sweating of the palm as a physiological response to this provocation. The results demonstrated that the subjects had the same stress response when the prosthetic hand was threatened as when the real hand was, but only during the periods when they experienced the third arm illusion. For instance, there was no stress reaction when the prosthetic right arm was replaced with a left arm or a prosthetic foot. ( Source: The New York Times )

HELPING THE ONES IN NEED: Approximately two million people in the United States are living with amputations, according to the Amputee Coalition, a national advocacy group. The results of the study may benefit patients by creating new applications in prosthetics research.