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be tested in a human subject. Indeed, there is a long path ahead until any of the retinal or brain implants can gain FDA approval, but the path might eventually lead beyond replacement to enhancement. Im- plants that use a video camera could draw on the advantages of tele- photo, wide angle, and zoom lenses to enhance bionic vision. The camera could also be made sensitive to infrared light,giving the wearer night vision, which could also be built into implants that use light sensors in the eye rather than a camera.

Apart from implants,approaches like laser surgery combined with adaptive opticsthe technique used in ground-based astronomical telescopes to correct light distortions caused by atmospheric turbu- lencecould bring us supernormal vision. The method relies on a wave-front sensor to examine the light waves; if they are not in per- fect step, the deviations are corrected by changing the shape of a mirror as the light reflects from it, producing an undistorted image. David Williams and Junzhong Liang, of the University of Rochester, have pioneered the use of wave-front sensors to map all the optical aberrations in a persons eye.This technique provides guidance for an advanced form of laser surgery, where the surgeon sculpts the cornea with tiny compensating corrections. In principle, all vision problems including astigmatism can be fully eliminated to give the fortunate patient 20/10 or 20/8 visionthe absolute best the human eye can do, given its density of rods and cones. Clinical trials have shown the effectiveness of the technique, which has given some people 20/16 vision.

In both natural and artificial beings, the senses are bridges be- tween the physical operations of a body and the higher operations of a brain or a mind. These sensory bridges carry us into the mental make-up of a digital being: its intelligence, its rational thought, its feelings if any, andif anyits consciousness.

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