The Phantom Hand
This illusion is extraordinarily compelling the first time you encounter it.
1. There is a very striking illusion in which you can feel a rubber hand being touched as if it were your own. To find out for yourself, ask a friend to sit across from you at a small table. Set up a vertical partition on the table, rest your right hand behind it where you cannot see it, and place a plastic right hand in view. Ask your assistant to repeatedly tap and stroke your concealed right hand in a random sequence. Tap, tap, tap, stroke, tap, stroke, stroke. At the same time, while you watch, they must also tap and stroke the visible plastic dummy at exactly the same time in the same way. If your friend continues the procedure for about twenty or thirty seconds, something quite strange will happen: you will have an uncanny feeling that you are actually being stroked on the fake hand. The sensations you feel will seem to emerge directly from the plastic.
2. Why does this happen? Matthew Botvinick and Jonathan Cohen, at the University of Pittsburgh and Carnegie Mellon University, who reported the so-called rubber-hand illusion in 1998, have suggested that the similarity in appearance feels the brain into mistaking the false hand for your real hand. They believe this illusion is strong enough to overcome the discrepancy between the position of your real hand that you can feel and the site of the plastic hand you can see.
3. But that is not the whole story. William Hirstein and Kathleen Carrie Armel of the University of California discovered a further twist: the object your helper touches does not even need to resemble your hand. The same effect is produced if they tap and strike the table. Try the same experiment, but this time get your acquaintance to rub and tap the surface in front of you while making matching movements on your real, concealed hand. You will eventually start feeling touch sensations emerge from the wood surface.
4. This illusion is extraordinarily compelling the first time you encounter it. But how can scientists be certain that the subject really believes that they are feeling sensations through the table? Kathleen Carrie Armel again and Vilayanur S Ramachandran learned that, once the illusion has developed, if you ‘threaten’ the table by aiming a blow at it, the person winces and even starts sweating. This reaction was demonstrated objectively by measuring a sudden decrease in electrical skin resistance caused by perspiration. It is as if the table becomes incorporated into a person’s own body image so that it is linked to emotional centers in the brain; the subject perceives a threat to the table as a threat to themselves.
5. This may all sound like a magic trick, but it does have practical applications. In fact, the experiments were inspired by work with patients who had phantom limbs. After a person loses an arm from injury, they may continue to sense its presence vividly. Often, the Phantom seems to be frozen in a painfully awkward position. To overcome this, a patient was asked to imagine putting their phantom arm behind a mirror. By then putting their intact arm on the reflective side, they created the visual illusion of having restored the missing arm. If the patient now moved the intact arm, its reflection – and thus the phantom – was seen to move. Remarkably, it was felt to move as well, sometimes relieving the painful cramp.
6. Beyond a practical application, these illusions also demonstrate some important principles underlying perception. Firstly, perception is based largely on matching up sensory inputs. As you feel your hand being tapped and stroked and see the table or dummy hand being touched in the same way, your brain asks itself, ‘What is the likelihood that what I see and what l feel could be identical simply by chance’? Nil. Therefore, the other person must be touching me.’ Secondly, this mechanism seems to be based on automatic processes that our intellect cannot override. The brain makes these judgments about the senses automatically; they do not involve conscious thought. Even a lifetime of experience that an inanimate object is not part of your body is abandoned in light of the perception that it is.
7. All of us go through life making certain assumptions about our existence. ‘My name has always been Joe,’ someone might think. ‘l was born in San Diego,’ and so on. All such beliefs can be called into question at one time or another for various reasons. One premise that seems to be beyond question is that you are anchored in your body. Yet given a few seconds of the right kind of stimulation, even this obvious fact is temporarily forsaken, as a table or a plastic hand seem to become part of you.
The text reports the findings of three teams of researchers. Match statements 1- 4 with the correct team A, B or C.
A. Botvinick and Cohen
B. Hirstein and Armel
C. Armel and Ramachandran
1. The illusion does not depend on the ‘phantom’ looking like a real hand.
2. The brain can disregard the spatial information.
3. If the fake hand is threatened, the subject will show signs of fear.
4. A hand-shaped object is required for the illusion.
Choose the correct letters A, B, C or D in answer to these questions.
5. How do researchers explain the fact that subjects respond physically when someone threatens to hit the table in front of them?
A. The table becomes an integral part of the image subjects have of themselves.
B. it is a reflex action triggered by the movement of the other person’s hand.
C. An electrical connection is established between the subject and the table.
D. Over time, the subject comes to believe that the table is one of his possessions.
6. What does the phantom hand experiment show us about the nature of human perception?
A. It is based on conscious thought processes.
B. It is primarily an unconscious process.
C. It is closely related to intellectual ability.
D. It relies only on sensory information.
7. Which of these statements best summarizes the wider implications of the experiments described in the text?
A. The experiments are valuable in treating patients who have lost limbs.
B. The experiments cast doubt on a fundamental human assumption.
C. The experiments show humans to be less intelligent than was once thought.
D. Human beings arrive at the truth by analyzing the evidence of their senses.
Complete the summary below. Choose ONE WORD FROM THE TEXT AND/OR A NUMBER for each answer.
It is a recognized phenomenon that patients who have been injured and lost (8) …………………… sometimes continue to have feelings, like pain or (9)……………………, in these parts of their body. In order to assist patients like this, doctors can use a (10) …………………… placed vertically on a flat surface. The patient imagines that he is putting his phantom arm behind the mirror and his (11) …………………… arm in front. When the patient moves the latter, the (12) …………………… also moves, giving the patient the illusion that his non-existent arm is moving- In some cases, this illusory movement may succeed in (13) …………………… the patient’s discomfort.
Answers for the passage The Phantom Hand
1 . B
2 . A
3 . C
4 . A
5 . A
6 . B
7 . B
8 . LIMBS
9 . CRAMP
10 . MIRROR
11 . INTACT
12 . REFLECTION
13 . RELIEVING