What does the word "cyborg" bring to mind? Is it Arnold Schwarzenegger's Terminator, the RoboCop, Cyborg from the Justice League? Well, in actuality the term – and hence the technology – nowadays is much tamer, and is expanding human capacities through prostheses and implants. One self-described "cyborg" is Neil Harbisson, an artist living near Barcelona, for whom color is quite literally music to his ears, thanks to an antenna he designed to overcome colorblindness.

Well-known in Spain and with an international following that enabled him to meet the likes of Leonardo DiCaprio and Tom Cruise, Harbisson is now testing out a new device designed to enable users to physically feel the passing of time.

Born in Northern Ireland with achromatopsia, a rare condition meaning he can only see in greyscale, Harbisson moved to Barcelona as a child and grew up obsessed with color and things he couldn't sense.

It was an obsession that saw the now 39-year-old Briton eventually go under the surgeon's knife to transform his identity and his life.

While at music college in England, he developed the slim metal rod that arches over his head and vibrates according to colors it detects.

At first glance it looks like wearable technology, but it's as much a part of his body as his nose or his ears, giving him the ability to "hear" the color his eyes cannot see.

"Being a cyborg means technology is part of your identity," he tells Agence France-Presse (AFP).

"It allows me to sense colors from infrared to ultra-violet through vibrations in my head that then become sound, so I can actually hear color."

‘Eureka moment’

In 2004, he managed to persuade a surgeon – who remains anonymous – to drill it into his skull, the technology becoming part of his body as the bone grew around it.

The sensor picks up the frequency of colors and translates them into sounds that he perceives through bone conduction.

Humans normally hear using air conduction with sound waves passing through the outer and middle ears and causing the inner eardrum to vibrate.

But with bone conduction, the vibrations are transmitted through the skull or jawbone directly to the inner ear.

The color-sound association also means he senses colors when listening to music or even speeches, with every syllable having a frequency that relates to color.

"At the beginning, everything was chaotic because the antenna was not telling me: blue, yellow, pink, it was giving me vibrations and I had no idea what color I had in front of me," Harbisson said.

"But after some time, my brain got used to it and it slowly became part of my perception and became normal," he added.

Although it cannot be switched off, Harbisson's antenna falls silent in darkness. His "eureka moment" came after dreaming "in color" and realizing the colors "had been created by my brain and not by the chip."

Although he may be the first person to "hear" color frequencies as notes, bone conduction helped Beethoven as he started going deaf. The German composer realized he could still hear by resting a wooden stick on the piano while biting the other end as he played.

Some 200 years later, bone-anchored hearing aids work in the same way via a metal implant inserted into the skull.

‘Stretch time’

In the home where Harbisson grew up and where his mother still lives, a riot of colored canvases line the walls, the staircase lined with curious-looking "facial scores" of celebrities like DiCaprio and Cruise.

These Hollywood stars let Harbisson detect the "sound" of their skin tone and lip color, which are rendered in enigmatic charcoal lines.

But Harbisson is now turning his attention to a new project.

He's created a device shaped like a chunky metal collar, designed to sense the passing of time, and is kicking off a year-long trial to see how it works.

"There's a point of heat that takes 24 hours to go around my neck and allows you to feel the rotation of the planet," he told AFP.

"Once the brain gets used to it, you can use an app to make subtle changes to the speed of the point of heat (that) should alter your perception of time," he added.

"You could potentially stretch time or make it feel like time is going faster."

For now, it's a permanent wearable rather than an implant. A previous incarnation had to be scrapped because he was "getting burnt" at 6:00 pm.

"This is an art that does carry some kind of risk but it's an unknown risk because we don't have much history of bodies and technology being merged," he said.