Sensing the world around us

 It's a widely held belief that when one major sense fails, others become super-sensitive to compensate. For instance, when one goes blind, their hearing improves. But is it true? 

• Some scientists suggest that it is not so much heightened sensitivity but more a case of heightened awareness and experience. When people have to rely on their other senses, they learn to use those senses more effectively, and perhaps their perception (how sensory information is interpreted in the brain) is altered, rather than their sensation.
• This explanation matters because, if it's even partly down to attention and practice, that implies that anyone can boost their sensory experiences and expertise.

• Here's something else intriguing. We are traditionally taught that we have five senses: vision, hearing, touch, taste and smell, a classification believed to have been devised by Aristotle.
• In fact there are more, but because there is no uniform definition of what constitutes a "sense," different scientists discuss different numbers of senses. Some scientists separate vision into two or even three senses, on the basis that colour, brightness and perhaps depth are all sensed by different mechanisms.
• Similarly, both taste and smell can be subdivided according to the different receptors used to detect different smells or tastes. As well as receptors in taste buds on our tongue, we have chemical sensors in our mouth and throat that contribute to flavour by detecting heat and cool sensations, as well as the "wow" factor of spices like chili.
• In the same way, we have two types of touch sensation relying on pressure sensors in the skin, one for light touch and one for deep pressure. And we have sense receptors in our skin for temperature, itch and pain — our pain sense can distinguish between mechanical, heat and chemical threats. As these rely on different receptors, some experts argue that they should be considered as separate senses.
• In addition, while our basic five senses communicate information about the environment outside the body, most scientists include at least two other senses that rely on communications from within the body and are responsible for balance and awareness of body position. Others would say that sensations such as hunger and thirst are "senses," too.

• However many we have, this wealth of senses filters our experiences of the world. The sense itself may prompt an instant reflex reaction, as when we withdraw our hand quickly from a flame, even before our brain determines the potential for a burn. But usually, incoming sensory stimulation is processed by the brain to create our perceptions — helped along with our memory and understanding.
• Our brain stores and organizes our sensory experiences so that we can function without having to learn anew each day. It's no good just remembering previous stimuli, they have to be categorized as well; you need a broad understanding of what a door handle does, otherwise every time you encountered one that didn't look quite the same, you'd be trapped in the room while you worked it out.This is also true with our concepts of "chair" or "table," "hot" or "sharp." Throughout our lives we build on these representations to expand our understanding of the world and our ability to operate within it. Using all our senses is crucial to this.
• Our senses also keep us safe. When we experience something outside those familiar categories, something that doesn't compute, our brain and our senses go into a state of high alert, to prepare us for the unexpected. They are especially attuned to detect change, because it may spell danger.