Magic of neuroscience -How accurate is our brain? Multisensory illusions |
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| One sensation can be manipulated by another. This helps us navigate the world and recognise objects. Multisensory systems are the ultimate cause of motion sickness and phantom limbs. For many decades it has been understood that different areas of the brain are specialized for detecting and processing different types of sensory signal, and yet, to be useful, the information coming through the different sensory organs must be combined. The mismatch between information from different modalities lies at the heart of a class of famous illusions that hint at the way sensory areas interconnect. |
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The brain relies on many senses, such as sight, taste, hearing, touch, smell balance and emotional state to make sense of the world that it interacts with. The integration of the many senses is crucial for the brain to make logical sense of its environment. Two perceived stimuli can produce a perception that is different from the sum of each stimulus. View the video on the right. This is known as McGurk's illusion. In this auditory-visual illusion you will see a film clip of a person saying "da da da." Nothing amazing about this. However, if you close your eyes, you will hear him saying "ba ba ba." Then if you turn the sound off and just watch his lips, you will clearly see that he is saying "ga ga ga." The effect happens because the brain does its best to reconcile mismatching information whenever it can. Ventriloquists exploit this by shifting what you hear to what you see (the dummy's mouth.) |
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| In the same vein, what you hear influences what you feel. In the parchment skin illusion, you rub your palms together while listening to different sounds. Higher frequencies will make you feel as if your hands are rough. Lower frequencies give you the impression of your hands being smooth, although nothing about them has changed.4 |
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