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Artificial senses can also open up a whole world of new human capa- bilities; as bionic implants, they can not only replace but even extend the natural senses.There is enormous interest in doing for the blind what cochlear implants have done for the deaf, as well as in other possibilities for bionic enhancement or replacement of human sen- sory organs.A limited experiment in direct human access to wireless communication was carried out in 1998 by Kevin Warwick, at the University of Reading in the United Kingdom, who had implanted into his arm a chip that emitted an identifying radio signal.The signal triggered functions such as turning on lights when he entered a room. However, the chip was not connected to his nervous system and did not carry out any functions of greater complexity.

Now under way are substantial efforts to restore sight to the blind through implants in the brain or retina. Most blindness is caused by a loss in the retinas sensitivity to light, although both the optic nerve, which transmits visual impulses to the visual cortex, and the visual cortex itself remain perfectly functional. This is what happens to people with the disease called retinitis pigmentosa, and to those with macular degenerationthe age-related condition that is the most common cause of blindness in the United States, responsible for loss of sight in 200,000 eyes per year. In these cases, retinal implants show promise for restoring sight.

When a nonworking retina is electrically stimulated, the brain perceives flashes of light called phosphenes.Nanoelectronic techniques have made it possible to embed a minute set of electrodes, a fraction of a centimeter across, in the eye atop the retina. In one recent ex- ample, a group led by Mark Humayun and Eugene de Juan, at the University of Southern California in Los Angeles, implanted such an array connected to a video camera worn by the blind person. The camera activates the electrodes, stimulating neurons to create phos- phenes that are related to the image registered by the camera. At the Illinois-based Optobionics Corporation,its foundersVincent and Alan Chow have eliminated the camera by implanting chips containing

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