The five senses are something we take for granted as we never even give a thought as to how complex the way we receive sensory information about the world we live in. As incredible the science behind all the senses may be, it is also interesting to see such intricate mechanisms being fooled by sensory illusions. An experiment that highlights how intricate the senses can be is that of the rubber hand illusion.
In this experiment, researchers made participants look at a dummy rubber hand, while obscuring their real hand from view. They then applied exactly the same stimulus to the real hand as the rubber hand, such as stroking it with a brush or feather. Within a short amount of time, the participants reported that they were convinced that the rubber hand was their real hand, confusing the visual sensation of seeing the rubber hand with the tactile sensation of their real hand being brushed.
Because the brain is so good at piecing together things to come up with explanations, it links the two sensations and thus concludes that the rubber hand must be part of the body. The association is so strong that some participants would even feel pain when the rubber hand was attacked, pulling away their real arm.
One of the lesser known senses of the body is proprioception – the sensation of knowing where your body lies in three-dimensional space. This sensation is what lets you do things with your eyes closed, while also being responsible for the feeling of embarrassing yourself with a fall when someone pulls the chair out from under you. Proprioception is based on a delicate “body map” your brain draws out from various sensory information such as your joint position and touch sensation from your muscle and skin. It then adds more information such as vision and spatial orientation information from your inner ears to accurately predict how you will interact in your environment. In the case of the rubber hand illusion, the brain is fooled into remapping the body map to accommodate the rubber hand.
The application of this phenomenon, known as multisensory integration, extends from out-of-body experiences to phantom limb pain, where amputees feel pain and sensation from an amputated limb. There are also anecdotal evidence of men with penile prostheses being able to achieve orgasms, most likely thanks to the rubber hand illusion.