Posted in Psychology & Medicine

Rubber Hand Illusion

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.


Posted in Psychology & Medicine


When you remember a scene from the past, you are not remembering the past. You are remembering a memory of the past. Your brain works in a very funny way where it does not record memories like film. Instead, it seems to remember things as a collage. Everytime you recall a memory – whether it be a happy memory of your first love, or a sad memory of lost love – your brain recalls your last recollection of the event. Simply put, every time you “remember” something, you are merely remembering the latest memory of the event. Each time you replay an event in your mind, it is rewriting a version of the memory over itself.

This means that the more you dwell on a memory, the more it is distorted. You romanticise the good parts and dramaticise the bad parts. The memory is ultimately warped beyond the point of telling the true story. Instead, it becomes something akin to a movie script or a fairy tale. But if it truly is a memory you deem special and hold dear, then maybe it isn’t too bad keeping a romanticised, “perfect” version of it somewhere in your heart to look back on every now and then.

Posted in History & Literature

The Oldest Trick

Magic has been a great source of entertainment for the masses for thousands of years. Across the globe, under many guises, magicians have amazed audiences with seemingly impossible “miracles” using misdirection and clever trickery. The oldest recorded trick – that is to say one performed purely for entertainment and not under the guise of religion or supernatural power – dates back to ancient Egypt.

According to the Westcar Papyrus, a magician by the name of Dedi was famous for his miraculous feats. The Papyrus tells the story of how Dedi was called to put a show on for King Khufu. He proceeded to decapitate a goose, then reattach the head, bringing the bird back to life. He repeats the magic with a duck, then with a bull, wrenching its head off then bringing it back to life by reattaching the head. For his amazing performance, he is rewarded by being allowed to live in the palace. This trick is still practised by magicians to this day, thus making it the longest performed trick in history.

Posted in Psychology & Medicine

Phantom Limb Pain

In up to 80% cases of amputations, a strange phenomenon occurs where the amputee reports sensation or even severe pain where the limb has been amputated. It was noticed in field hospitals during wars when a soldier would wake up and ask someone to scratch his leg – which was no longer attached to his body. The sensation can be so powerful that victims actively believe that their phantom limb can interact with real objects. For example, there have been case reports of patients trying to pick up a cup with an amputated arm and becoming frustrated with their inability to.

Phantom limb pain may persist even after the amputee realises the limb is no longer there. The basis for phantom limb pain is a neurological system called the cortical homunculus. The cortical homunculus is a concept that the part of the brain responsible for sensation and movement is mapped out so that each part corresponds to a part of the body (see picture). For example, the top of the primary somatosensory and motor cortices (said parts of the brain) is responsible for foot sensation and movement while the side receives information from and sends signals to the face. It lets the brain construct an image of what the body looks like from sensory information it collates from various body parts. It is suggested that phantom limb pain is caused by a remapping of the cortical homunculus, fooling the brain to think that the limb is there even if it has been physically cut off. This also explains a similar condition called supernumerary phantom limb, where the brain believes there is an extra limb (e.g. a third arm).

As the homunculus concept is a recent idea, treatment options had not advanced much until the late 1990s. In 1998, a neuroscientist called Dr. Vilayanur S. Ramachandran devised a method called the mirror box treatment. He noticed that victims of phantom limb pain (PLP) had paralysis or pain in the limb just before the amputation (such as tightly gripping something before the arm got blown up by a mine), suggesting that PLP may be a form of learned paralysis. This means that the brain believes that the arm is still paralysed and any movement causes an uncomfortable sensation as the brain thinks the limb is contorted into a painful position. To fix this problem, Dr. Ramachandran invented a box with two holes, each going into a separate compartment. One compartment is for the good arm while the other has a mirror positioned on an angle to reflect the other arm (instead of seeing the stub they put in the hole). He would then instruct the patient to perform symmetric movements with both hands while looking at the reflected arm. For example, he would tell the patient to squeeze their “fists” tightly as possible and then let go. Through this procedure, the brain is retrained to let go of the perceived paralysis and pain as it is tricked in to thinking that the arm is healthy again. The mirror box therapy drastically improved the outcome and quality of life of PLP patients through the power of illusions.


Posted in Psychology & Medicine

Sensory Illusion

The five senses we use to experience the world are simply wondrous. However, thanks to our not-so-perfect brain, these senses can easily be distorted. Illusions are a very good way to show how the brain processes sensory information and there are many fascinating examples.

Almost everyone has seen an optical illusion before, such as Penrose’s endless stairs or the Muller-Lyer illusion. There are countless more examples such as static pictures that appear to be moving and illusions in colour perception (A and B are the same colour). This is caused by the brain not recording images like a camera, but rather processing visual information and reconstructing an image. There are four main types of optical illusions: ambiguous (e.g. rabbit or duck), distortion (Café wall illusion), paradoxical (Penrose triangle) and fictional (only seen in hallucinations or by schizophrenics).

(Do you see the dolphins? Children cannot see the man and woman because they cannot comprehend it, whilst adults cannot overpower the sexual image)

Like vision, every other sense can be fooled in a similar fashion.
Auditory illusions that distort what we hear are fairly common, a good example being the infinitely ascending Shepard scale (which are just a series of the same ascending octave scale). Also, the McGurk effect shows how the brain uses a multimodal approach where it involves both hearing and vision when listening.

There are also tactile illusions. For example, if you pull your top lip to left and the bottom lip to the right, then prod the middle of the lips with a pencil, it feels like there are two. However, the more famous case is of the Phantom Limb, where an amputee’s brain still believes that the limb is there, causing it to “feel” the limb or even feel pain.

The other two senses aren’t as famous in terms of illusions, but definitely exist.
Smell is easy to fool through chemicals as it is the physiological method of detecting smell. It also exhibits olfactory fatigue where it becomes desensitised to a strong smell.
Taste illusions are more fascinating and easily seen. They are caused by two or more tastes forming a synergy to produce a completely different taste. For instance, mixing barley tea and milk produces a coffee milk taste, while cucumber and honey tastes like melons.
A more fascinating illusion involves Miracle Fruit Berries, which contain a substance called miraculin that distorts the taste of sourness to sweetness.

This shows how we can fool all five senses, and learn more about the mysterious organ that is the brain.