ART / Earning her stripes: Like many abstract artists, Bridget Riley believes that her work has been misinterpreted. She talks to Andrew Graham-Dixon

Bridget Riley does not see things in black and white. 'All artists are mixtures,' she says. 'They are complicated. I don't think they are one simple thing.' The remark may conceal a certain irritation since Riley, who was 60 last year, has had to work unusually long and hard to convince people of her own complexity. She is one of those artists for whom early fame may, in retrospect, prove to have been as much a handicap as an advantage. Next week sees the opening, at the Hayward Gallery, of an exhibition devoted to Riley's paintings of the last decade. But she still remains, in many people's minds, inextricably identified with the era in which she first came to prominence - someone who, along with the likes of Mary Quant and Twiggy, helped to create one of the distinctive 'looks' of the Sixties. Riley has been remembered as a pioneer of Op Art, the creator of canvases whose weird effects - dancing dots or pulsing curves, black on white grounds, designed to induce dizziness - seemed to sum up the spirit of the times. Her disorientating paintings seemed like the visual accessories of LSD culture: psychedelia, so to speak, without the colour.

But maybe it was all a terrible mistake. People began to get her all wrong, as far as Riley is concerned, as early as 1965, when she was included in a group show called 'The Responsive Eye' at the Museum of Modern Art in New York. 'I was terribly disappointed with the American response to my work, because at that time it seemed as though the best critical minds were over there, and I wanted to know what they really thought. Well, there was no chance: the hullabaloo knocked out all serious consideration. People complained about how aggressive the paintings were. I was seen as a kind of tough, outrageous, pattern-making artist. From then on I was seen as a quasi-designer, a designer manque'. The impression was strengthened by the appearance, just as the American exhibition opened, of a line of women's clothes (the first of many) made from fabric loosely based on Riley's paintings. They were designed - an unusually direct collision of the worlds of fine art and fashion - by one of MOMA's trustees, who had bought a couple of paintings from the show. 'Half of the people at the opening were wearing them.' Riley was not amused.

The notion of Riley as 'a quasi-designer' went hand in hand with another, equally damaging (as she sees it) notion of her: as prophetess of a new, super-cool approach to the making of paintings; as a quasi-scientist, in effect, whose true interest lay in areas like optics or habits of visual perception. Riley may have inadvertently contributed to this idea, by talking about her paintings as if they were controlled experiments. In 1965, she told the American magazine ArtNews that 'The basis of my paintings is this: that in each of them a particular situation is stated. Certain elements within that situation remain constant. Others precipitate the destruction of themselves by themselves. Recurrently, as a result of the cyclic movement of repose, disturbance and repose, the original situation is restated.'

Riley's image as an essentially conceptual artist, a white-coated figure who treated the studio as a form of laboratory, was enhanced by her practice of employing assistants to fabricate the paintings themselves - a method which Riley still follows, seeing herself as in essence a 'composer' of images whose execution can be left to others. These days, she still feels the need to insist that 'this whole scientific thing is not true, it's got nothing to do with my paintings. God, I've been given so many bloody books on optics and mathematics. I'm always polite, I always thank whoever it is - but I never even open them.'

Riley's predicament, her belief that her work has been consistently misrepresented, may be the inevitable predicament of every abstract artist. Abstraction, having no overt theme or subject, is a form of art peculiarly open to (mis)interpretation, and its history is pimpled with the laments of painters who believed themselves to have been misunderstood. But during the last decade, Riley has taken matters into her own hands and gone about the business of redefining herself with considerable energy.

The new, revised Bridget Riley made her most conspicuous appearance in 1984, when she wrote an article for Vogue called 'On Swimming through a Diamond'. Instead of Riley the systems analyst, this revealed an altogether different artist. The new Riley was a figure who seemed to want to place herself squarely within the English Romantic tradition, an artist whose great concerns were the experience of nature and its expression in art. In the article, Riley lyrically recalled her childhood in Cornwall in the 1930s, amid 'changing seas and skies, a coast line ranging from the grand to the intimate, bosky woods and secretive valleys'.

She went on to list a sequence of memories, charged with significance for her art: 'Swimming through the oval, saucer-like reflections, dipping and flashing on the sea surface, one traced the colours back to the origins of those reflections. Some came directly from the sky and different coloured clouds, some from the golden greens of the vegetation growing on the cliffs . . . The entire, elusive, unstable, flickering complex subject to the changing qualities of the light itself.' Suddenly, all Riley's art - ranging from those early Op Art paintings to her subsequent work, with its pulsating bars or waves of colour - appeared, so to speak, in a new light. So that was what it was all about. Nature. Bridget Riley was a very English sort of artist, after all.

Well, perhaps not entirely. 'The idea of art as equivalents for states of being, that has always meant a lot to me,' she says. 'That's a big (she thumps the table) old part of my roots.' But those roots seem to lie more in French than English art, and specifically in the French art of the early modern period. Riley talks with great enthusiasm and admiration about late Monet, about Cezanne and Van Gogh and Seurat. Her own art might be said to express, or embody, in a yet more abstracted form, a certain late-Impressionist conception of the world: as a place of indeterminate, constantly shifting energies, a field of light and colour in which forms seem constantly threatened by their own dissolution.

Even Riley's earliest black and white paintings may be seen as distant echoes of the visions of early modern French painting, since their subject is the truancy of vision: their mobile, distorted geometries of circle and triangle, dancing and floating before the eyes, make them into metaphors of the fact that nothing seen ever stands still. They can also, however, seem like metaphors for states of psychological unease, mental disequilibrium: images of order poised precariously on the edge of destruction. Riley is drawn by what she sees as a similar sense of threatened visual order in late Cezanne - 'the way he breaks it up, turns the canvas inside out so that what should logically be furthest away seems closest, and vice- versa'. In her own art, that same process of 'inside-outing' is just as turbulent. She says she does not think of herself as a particularly anxious artist, but there may be more angst in her art than she is willing to concede.

If Riley's art could be said to have been constructed around any single idea, it may be her conviction that 'nothing that I see is ever the same twice. You know the experience of seeing something wonderful and then going back to find it again and realising that it's just not there. What you saw has gone: the object might be the same, but the light has changed, and the experience you had in the first place can never be got back.'

Riley, who says she retains ('thank God I do') an almost childish sense of wonder at the visual appearance of the world, finds it odd that people should find her work difficult or remote. 'What happens in the world - whether you're just out walking in the park, or wherever - is so visually extraordinary if you actually see it for what it is. Yet people can absolutely deal with these amazing visual events that surround them, the way the sky is and the way the light falls: they can sit in the middle of all this, yet when something just faintly, faintly as violent and amazing is on a canvas they have problems with it.'

Usually, Riley says, she sets out to evoke natural references in 'an elliptical way'. She gestures to a recently completed painting on the wall of her studio, a jigsaw of coloured diagonal forms (she calls them 'zigs' since each one is, in effect, the ascending half of a zigzag) and says, 'It's not only nature, but I need to recognise something as a sensation within parts of the painting. This (she points to a sequence of violet 'zigs', running brokenly across the canvas) might be a shadow area, and that violet might, so to speak, be playing a shadowy part. If I've got it right it will somehow echo in me, the feeling that shadows do have that kind of movement: they break and they reappear and they filter.'

Riley has followed an unusual course, for an abstract artist, in that she has tended to complicate rather than simplify her art as she has gone along. In the 1970s and 1980s, she became increasingly preoccupied with minute nuances, with the tiny, subtle energies that could be generated by alternating bands of different colour. It was an art of rhythm and interval where, in her words, 'the whole thing is really made up of edges, of how one edge meets another and what happens when it does.' The result was, too, an art that seemed to aspire to the condition of music: painting built on the principles of tonal modulation, devoted to counterpoint and harmony.

Riley evolved her current idiom of more broken, crystalline forms partly because she felt that 'for years there had been these stripes that tied the painting to the flatness of the picture plane - but I wanted to be able to create a sense of volume, of masses.' Half way through the 1980s, when the National Gallery invited her to select one of its series of 'Artist's Eye' exhibitions, Riley was suddenly struck by 'the marvellous way in which those old painters always gave the eye something to do - beyond storytelling, or narrative, it's more to do with leading the eye around the painting in an extraordinarily complex number of ways, so that you can go on looking and looking. And it seemed to me extremely sad that modern painting wasn't offering that.' Riley sees her new technique as a way of 'building spaces' in abstract art that can be as various and enriching as those of Old Master painting.

Riley's recent pictures are, as emphatically as any of her earlier work, meant to be 'equivalents to experience'. 'For instance, I've done a painting called High Sky, and although none of the shapes in it could really be related to the sky in a straightforward way there is a certain skyish feeling to the painting. You know those great cumulus clouds in a big sky - how they contain these amazing contrasts, this terrific white and blue, this gigantic happening, which is piling up. The painting is nothing to do with a piece of sky, but it's the sensation of that, and these extraordinary pockets and places in those clouds.'

Whether Riley has succeeded in her self- appointed task remains to be seen. She can try to distil an experience and put it down on the canvas, but will that experience, once abstracted, remain sufficiently intact to communicate itself? The art is the test. Will visitors to the Hayward see a high sky or merely a brightly coloured kaleidoscope of geometrical forms? Is Bridget Riley on to something, or does she have her head in the clouds?

Hayward Gallery, London (071-928 8800) 17 Sept-6 Dec

(Photograph omitted)