Optical illusions can be fun games. It's an old lady! It's a young woman! Old lady! Young woman! Both! Neither! But they have been used for medical treatment purposes. And it's also been postulated that they may have played a role in causing one of the greatest disasters in recent history.
Phantom limb pain is the sensation of pain in a body part that has been amputated and no longer exists. While doctors have tried to treat this phantom pain with medicine, physical therapy and even surgery, some of the most successful treatments have been with what is essentially an optical illusion [source: Kim]. For this brain trickery to work, doctors have patients place their existing limb – for example, their right arm – on the reflecting side of a mirror, and their brain is fooled into believing the illusion that the reflection of their existing arm is actually their amputated left arm. While the patient understands this not to be true, the brain is tricked into thinking the arm has returned. The pain often disappears after multiple sessions playing with this mirror treatment [source: NPR].
As much as this optical illusion has helped amputees, illusions may also have been responsible for causing some harm to folks as well. Historians have postulated that the sinking of the Titanic may have actually been the result of an optical illusion at play. The atmospheric conditions on the evening that the ship sank were ripe for super-refraction or the extreme bending of light. This light bending may have caused the iceberg with which the ship collided to visually disappear from sight. Not only that, but after the collision, the Titanicitself may have the victim of this light-bending, making it hidden from the sight of the nearby freighter, the Californian, which should have been able to come to its rescue [source: Smithsonian.com].