Senses

• A cochlear implant gives a deaf person hearing In wide use

  A microphone behind the ear turns sound into electrical pulses, and a thin wire threaded into the inner ear delivers them straight to the hearing nerve, skipping the damaged parts of the ear. People who were profoundly deaf hear speech again, and children born deaf learn to talk. It is the most widely used sensory implant there is, and the only upgrade on this branch at the top of the ladder.

• A gene therapy restores sight in an inherited blindness In clinical use

  Some children are born with a broken copy of a single gene the retina needs, and go blind in childhood. A working copy of the gene, carried by a harmless virus, is injected under the retina once, and the cells start making the missing protein. People who could not walk an obstacle course in dim light can do it afterwards. It was the first gene therapy for an inherited disease approved in the United States, and the first upgrade of a sense done by changing a person's genes.

• An implant gives a blind person back some sight In clinical use

  A camera on a pair of glasses sends pictures to a grid of electrodes on the retina, and a person who had lost all useful sight sees spots of light again: enough to find a doorway, follow a line on the floor or tell where a window is. It is the first upgrade of a sense to go all the way from a laboratory to a device a doctor could prescribe. The device that got it there, the Argus II, was later taken off the market by its maker, which does not lower the stage: the ladder records the furthest a technology has reached.

• A device gives a person a sense no human is born with First human

  The other upgrades on this branch give back something lost. This one adds something no one has had: a feeling for which way north is, for a magnetic field, for infrared light. The first study to do it properly put a belt on volunteers that buzzed on whichever side faced north, for weeks at a time, and found that some of them came to feel direction rather than think about it. Others have had small magnets put under the skin of a fingertip to feel electrical fields. It is a first human, done outside medicine and mostly outside the clinic.

• A gene therapy restores hearing in a child born deaf First human

  Children born without a working copy of one gene (OTOF, which makes a protein the inner ear's hair cells need to pass sound on to the nerve) are profoundly deaf from birth. A working copy, injected into the inner ear once, let most of the children in the first trial hear speech within weeks. It is the first time a sense missing from birth has been restored by changing a child's genes.

• An implant in the visual cortex gives sight with no working eyes First human

  When the eyes and the optic nerves are gone, the only way to put a picture into a person is to stimulate the part of the brain that sees, at the back of the head. Electrodes there make a blind person see spots of light, and enough spots in the right places make a shape. The first person had this done in 1968; the first with a modern camera-driven grid, in 2018. None of it has left the laboratory, and the pictures are still a few dozen spots, not sight as a sighted person has it.

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