The other illusion is that you are looking at something ‘out there’. In reality, because it is the brain creating the images, all is happening inside your brain. There is no ‘out there’ at all. Even the fisherman is perceived inside your brain. Even though you may put your hand out and feel the cold of the river, you still can only see the river from inside your head. Another strange effect to notice is that when our retina receives the light, the image that is formed is upside down. Our brain corrects this so that everything appears the right way up.

The sound that reaches your ears travels at 770 miles per hour, which is considerably slower than the speed of light. This means that, if the fisherman is singing, then the image of his mouth moving reaches you much faster than the sound. This effect can be noticed if you are a few hundred yards away from the start of an athletic race that is started by a starting pistol. As the gun is fired you see the smoke arise from the barrel before you hear the sound of the gun firing. The speed of sound can also vary according to temperature and the altitude. The higher and colder the air is, then the slower sound travels. The medium in which sound travels also affects its speed - whether this be water or glass for example.

You put your hand into the river. How long does it take for you to feel the river? As you touch the river, impulses travel through the nerve network in your body to your brain. Normally the rate at which these impulses travel is about 331 metres per second. This is a bit slower than the speed of sound at around 346 metres per second at 82 degrees Fahrenheit.

What at first appears to us as a simple situation - sitting on a river bank, seeing a scene, being aware of the smells, touching the water, thinking about what you are seeing, is an extremely complex mechanism. Energy in the form of light is being received by your retina, sound waves reach your ear drums, odour molecules reach your nose, nerve impulses enter your brain, electrical impulses occur in your brain that we call thinking. All these different forms of energy travel at different speeds - yet we view it all as if it takes place in the now or the present. It is our mind that processes all this information to create what appears to be ‘reality’ - yet the way we comprehend all this is an illusion created by us to make sense of it all. Indeed we must make sense of it all, otherwise it would be impossible to live in this physical world. We need to be able to walk, avoiding objects, react to the sound of a roaring lion so that we can take flight before it pounces and eats us.

It is our brain that makes sense of everything we see - but can we trust our own brain?

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