Imagine you're in a dark room, running your fingers over a smooth surface in search of a single dot the size of this period, How high do you think the dot must be for your finger to feel it? Scientists have determined that the human finger is so sensitive it can detect a surface bump just one micron(l0-6m)"high. The human eye, by contrast, can't tell anything much smaller than100 microns.No wonder we rely on touch rather than eyesight when faced with a new roll of toilet paper. Biologically, touch is the mother of all sensory  systems.It is an ancient sense in evolution: even the simplest single-celled living things can feel when something brushes up against them and will respond by moving closer or pulling away. It is the first sense aroused during a baby's development and the last to weaken at life's peak. Patients in a deep coma  who seem otherwise lost to the world will show skin reaction when touched by a nurse. "Touch ,is so central to what we are that we almost cannot imagine ourselves without it," said Chris Dijkerman."It's 'not like eyesight, where you close your eyes and you don't see anything. _ .It's always there." Long ignored in favor of the sensory heavyweights of eyesight and hearing, the study of touch lately:: has been gaining new concern among scientists.They're exploring the effects of recently reported false touch impressions, of people being made to feel as though they had three arms, for example, with the hope of gaining the true understanding of how the mind works. Others are turning to touch for more practical purposes: to build better touch screen instruments and robot hands, a more well-rounded virtual life.. "There's a fair amount of research into new ways of offloading information onto our sense of touch," said Lynette Jones. "To have your cell phone buzzing (making a low sound) as opposed to ringing turned out to have a lot of advantages in.some situations." Touch is our most active sense, our means of seizing the world and experiencing it 'first hand. Dr.Susan Lederman pointed out that while we can become aware of something by seeing or hear,ing7;-.from a distance and without really trying, if we want to learn about something by means of touch, we must make a move.We must rub the cloth, or pet the cat. Touching is a two-way street, and that's not true for seeing or hearing. If you have a soft object and you squeeze it, you change its shape. The physical world reacts back." Our hands are smart and can do many tasks automatically - button a shirt, fit a key in a lock, play the; piano for others.Dr.Lederman and her colleagues have shown that blindfolded subjects can easily recognize a wide range of common -objects placed.in their hands.But on some feeling tasks, touch is all thumbs (very clumsy). When people are given a raised line drawing of a common object, they're puzzled."If all we've got is outline information;" Dr.Lederman said,."no weight, no texture, no temperature information, well, we're very, very bad with that." Touch also turns out to be easy to fool, Among the sensory tricks now being investigated is something called the Pinocchio illusion. Researchers have found that if they shake the band of the biceps , many people report feeling that their forearm is getting 'longer, their hand floating ever further from their elbow . And if they are told to touch the forefinger of the shaken arm to the tip of their nose, they feel as though their nose was lengthening, too. The sense that is firstly awaked during a child's development is the sense of  _  .
sight taste hearing touch