The world of our experiences owes as much to our minds as to the world outside. All our experiences – sights, sounds, smells, and tastes – are our mind’s interpretation ions of the physical reality that exists around us. Without a mind to perceive it, a sound is just a pattern of vibration in the air. So, our perceptions are all, in essence, an elaborate form of ‘virtual reality.
Imagine that you have landed on a strange planet. You leave your spacecraft but are unable to make out anything at all; you feel nothing, see nothing, hear nothing. Dack inside your craft, you consult your instruments and discover that there is, in fact, a rich diversity of matter and energy crisscrossing this new world. There are electromagnetic waves, vibrations, and molecules – it is just that they are so different from those on Earth that your body has not evolved to be sensitive to them. They are like the high-pitched sound waves that bats use to communicate or the infrared light- waves that can be seen by night- owls.
Consulting technical manuals onboard, you design a suit that can detect these alien forces. You build in sensors to pick up the vibrations, cells that respond to the electromagnetic waves, and receptors for the molecules that are carried around in the planet’s atmosphere. Then, you make a transducer that turns the suit’s responses into stimuli that your body can understand. Wrapped in the suit, you step out again into your new world. This time, it is a place filled with objects and resonating with sound, color, taste, smell, and touch.
Our bodies are like that spacesuit. Just as the alien world can only be perceived when we equip ourselves with appropriate sensors, our world comes into existence only when the brain and our nervous system translate its energy forms into the experience. What we think is a view of something ‘out there is, in fact, a sensation created by the brain from the messages received through the sense organs. In his sense, it is not so much reality itself as ‘ virtual reality. The reason why we all perceive the world so similarly is that we all have similar nervous systems – we are all wearing the same type of spacesuit. But how do our brains create conscious experiences from the patterns of energy in the environment?
Constructing experience
A perceptual experience – such as seeing an object, hearing a sound, or feeling a texture – occurs when matter or energy in the outside world stimulates our sense organs. For example, when we see so much ng, it is because light rays of the correct frequency hit the retina, which then sends signals via the optic nerve to the visual cortex at the back of the brain. Here, the information is decoded and turned into a raw sensation. From here, the information passes to the frontal lobes, where it is interpreted conceptually and becomes a conscious visual experience, identified as a familiar – or unfamiliar – object.
However, the flow of information is not excluded from the sensory to the conceptual area of the brain: the neural pathways run in both directions. When we imagine an experience or call up an image from memory, the flow is reversed. Activity in the frontal region of the brain generates a concept, which passes to the sensory cortices and prompts them to produce appropriate sensory signals. These are then fed forward again, where they are experienced as sensory events rather than just as abstract concepts. En route, they may trigger activity in the limbic system, producing emotions as well. The more the sensory cortex is stimulated, the more vivid the recollection – so imaginary sights may vary from vague impressions to hallucinations so real as to be indistinguishable from the real events.
For example, if you think of a concept such as ‘going swimming tomorrow,’ the frontal region of the brain stimulates the sensory cortex to produce the neural activity that would normally occur when the body is immersed in water. It may also produce the sort of activity in the visual cortex that would normally be triggered by the sight of water – perhaps a swimming pool or the sea. The image may be very crude – just an impression of water – or highly embellished to include the people you expect to be swimming with, the beach you will be visiting, the feeling of the sun on your skin, the swimming costume you intend to wear. In addition, the thought may trigger dopamine release in the limbic system, which provides a frisson of pleasure – just as though you were experiencing your swimming trip for real.
The Power Of Imagination
The detail and vividness of our imagined or remembered imagery depend largely on our ability to focus attention – that is, to limit our brain’s activity to the imaginative process. Because many areas of the brain are involved in creating an imagined scenario, any competing cognitive activity will divert resources away from the task. In order to daydream. Successfully, you must clear your mind of other things and attend to them – just as you have to attend to significant things in the real world.
Internally generated experiences are rarely as rich as those created by outside stimuli because, for very good reasons, the brain is designed to give primary attention to the outside world. If daydreams were as tangible as ‘ real’ experience, then we might well fail to notice things that may pose a physical threat, or we might respond physically to events in our imaginations. So, the sensory activity associated with daydreams is easily interrupted by signals coming in from outside. If you are visualizing a sunny day, for example, the image will be shattered if your eye tests a big object moving towards you. This is why daydreamg is difficult in a busy, exciting environment – but seductively easy when there are few distractions.
The Realm Of Our Senses
Our sensory system has evolved to pick up the type of information that is most useful for our survival. We can see light only in a small part of the electromagnetic spectrum. However, this part includes the wavelengths of light that certain key chemicals in our bodies and environment reflect. For example, hemoglobin and chlorophyll reflect in this range – so we see blood as bright red and plants as bright green. Similarly, the sounds we hear come from a narrow range of vibrational frequencies, so we cannot hear the shrill echolocation signals of bats, for example – but these are of no benefit or threat to us. If we could redesign our sense organs so that they pick up a different range of stimuli, the world would be very different. We would see different colors, smell many more smells, and hear things that we are usually deaf to.
A world without red
Some people’s vision is abnormal because the retinal cells are insensitive to red, green, or blue. The top picture shows what these red tulips might look like to someone without red vision. Not only are colors changed, but the relative contrasts are different – the blue flowers stand out far more than the red.
Two-Way Processing
Conscious perceptions of the outside world are produced in the brain via a combination of bottom-up and top down processing. Raw visual data from the eyes is sent to an area of the brain at the back of the opposite hemisphere, where ‘bottom-up ‘ processing begins. This continues as the perceptual information travels forward, with meaning added at each stage. Meanwhile, conceptual information (such as memories, expectations, and verbal labels) is constantly fed back from frontal brain areas. This ‘top-down’ process integrates the perception into the existing conceptual framework and brings it to consciousness. The final perceptual experience is thus unique to each individual.
The Limits Of Imagination
When you imagine an object or an event, it may at first seem just as clear and detailed as a ‘real’ experience. But if you test it out, you will usually find the imagined experience is full of gaps and indistinct: its clarity is an illusion. You can try this by summoning up a familiar image – some patterned curtains in your house, say. Close your eyes and concentrate on one particular part of the image – the pattern near the top, for example. When you have fixed the image clearly in your mind, zoom in on one part of the pattern – say, a flower. Can you see its form in detail?
Can you even state exactly what colors are in it? When you try to capture these details, the haziness of the image becomes apparent – very few people can visualize all the details. This may be because imagination depends more on top-down processing, whereas externally generated images are produced by the proportionately more bottom-up activity. Both give the subjective impression of dense sensation, so the experience is very similar. But the actual amount of sensory information contained in imagined experience is relatively sparse – our brains ‘fill in’ the missing bits.
Time to daydream
The fantasies we weave when daydreaming are most easily summoned when we have few distractions. Although they can be very vivid, these inwardly created perceptions are rarely as detailed as ones that we actually experience.
