For an artist whose work is so visually bold, Turner prize nominee Mark Titchner is a slight, nervy figure. In between drags on his roll-up, he worries about newspaper art-critics commenting on his work. "I don't want to read any of the stuff in the papers in case it affects the way I work. I have to keep on doing what I do, whatever anyone else's opinion is. My mum will collect all my cuttings and if I want to I can read them later," he says.
His dark brown hair has been ruffled by nervous hands and his astonishingly blue eyes move restlessly over the chaos of his studio on Bermondsey St in London. He apologises for the mess. It's not normally this bad, he tells me. But the building is about to close and all the artists booted out to make way for smart new flats - it's just one more thing for him to worry about, with the fact that he's barely been able to spend any time with his girlfriend, social worker Clare Ewer at their new place.
Seeing a piece by him for the first time is a slightly creepy experience. The Invisible Republic is a fibreglass banner, the height of a house, on which is painted: "We want mutual loyalty and we want to realise potential and we want to improve the human condition and we want unyielding integrity and we want to shape the world's future and we want inspiration energy and excitement and we want to make dreams a reality and we want your contribution and we want continuous improvement and we want to be open and transparent."
The words have a chilling, almost familiar, relevance. This makes sense when you realise Titchner pilfered them from the corporate manifestos of 10 leading global consumer brands. The slogan style, the "we want", comes from the Black Panther's 10-point programme, a document that called for staples like bread, housing, education and justice. The language of a US black civil rights movement, that once stood for things that mattered, now has the hollow beat of advertising speak. It's this continuous movement of ideas and values, our beliefs and faith - how formerly powerful language becomes anodyne - that fascinates the 33-year-old artist.
"There's a history of brilliant ideas disappearing off into the ether because they don't do certain things, or act in a certain way. They don't fit into the time. The quotes I choose represent things that might have happened, like an alternative past," he says.
It's the text that makes his work. He has two rules: the quote can come from anywhere and the language must be simple. The sources are chaotic and there's no way of figuring out where they're from. It might be a lyric from Black Sabbath, a religious text, a political manifesto, a scientific paper or a work of literature.
He had the idea back in 2000 when, sitting in his mum's back garden at home in Luton, he realised that the pure geometric abstraction he had developed during his time studying Fine Art at St Martin's wasn't really going anywhere for him.
"The drawings were ambient. People could walk past them without really analysing them, and I thought, 'If I just write a word over the top it changes everything'. You engage with it. We react to language in a completely different way; you can't stop yourself from reading a word. It's a real moment of power," he says.
That illumination became more literal when he started to transfer his work onto light-boxes - a ploy used by advertisers to attract a potential consumer's attention.
By using their language, he hopes to make it clear what they are doing to your head. And, like commercials, his aesthetic grabs the eye, stopping you in your tracks. A work from 2003 is a case in point. The candy-coloured psychedelic imagery intensifies the sickliness of a text that reads: "If you can dream it, you must do it". An open palm emitting rays of light, like the omnipotent hand of God in evangelical posters, adds a further touch of battiness to the quote, which was pinched from a book review of an obscure and untranslated French science book called Absolutely Inhuman. It appears that Titchner means it.
"It's about making a clear text about normal people coming into a gallery-space and potentially extending their powers. It's about us becoming greater than we think we are. I'm not mocking the idea of self-improvement."
Does he want to change our behaviour then, just like the powers he is criticising?
"I suppose I would like people to feel that, when they are absorbing this information in their daily life, they are more reflective. That they are aware of what's going on. That they realise how they are being manipulated," he says.
The idea that there are invisible forces assailing our consciousness is hardly news. What may be clearer is his brilliant wit in the juxtaposition of references, visual and textual, in his work.
His mammoth mechanical sculpture Ergo Ergot, made specifically for the Turner Prize exhibition and to be unveiled on Monday, demonstrates beautifully what he is about. Even the title has a clever twist. "Ergo" is from the foundation of rationalism argued by Descartes with cogito ergo sum ("I think therefore I am"). Ergot is a hallucinogenic wheat fungus that Albert Hofmann was working on when he discovered LSD.
This trippy idea of the nature of reality is made optical with two illusions carved into large spinning wooden "roto-reliefs" (based on a technique derived from Marcel Duchamp). They form a geometric arrangement called the Titchner Illusion, designed by an early 20th century psychologist, Edward Titchner - freakishly he and Mark share a surname. It's a trick where a circle surrounded by other circles will appear smaller if the surrounding circles are larger. Titchner uses this, and a technique that makes a two-dimensional disc appear to be a three dimensional cone, to make our minds start spinning.
A sound installation and flickering video-screens on either side of the sculpture have been designed to induce a mathematically precise trance-like state where the brain is believed to be at its most receptive. A dark blob, based on the Rorschach ink-blot used in tests by psychologists, undulates as 21 dates flash up, each for a tenth of a second - they are key dates identified as moments when legislation was passed which seriously eroded our civil liberties.
There's a lot going on. It's like an Orwellian mini-state laid bare. Titchner puts his concern with the insidious forces at work in our world down to a conventional childhood in Luton where he went to the local school and everything was how it appeared to be - until he left that safe cosy environment to enter the big wide world, in London. The shock stayed with him.
He says: "I was very aware of when I was a child that this was the right way of doing things and that was wrong. It had a lot to do with growing up in the arrogant certainty of the Thatcherite age. Those certainties that I used have, I now view with extreme doubt."
He even doubts the Turner Prize. "I don't know if I want to win or not. It's an unknowable situation," he says. "I'll have to go back to being a normal artist in a few months time when all this is over."
The Turner Prize exhibition is at Tate Britain from 3 October to 14 January ( www.tate.org.uk; 020-7887 8888)