Op Art’s great pioneer Bridget Riley first developed her revolutionary approach to painting, not in the vivid colors that she can make surge and retreat before our eyes, but a simple, uniform black and white. As a new exhibition at Dia Beacon featuring six of her key works from the 1960s makes clear, it was by reducing her palette to essentials that she was first able to achieve the dazzling optical effects that have defined her career for over 60 years. In these early paintings the distance between lines, the tilt of an angle, even the slightest compression, can result in entirely different bodily and perceptual responses.

In the fiercely visceral Burn (1964) for instance, an intricate grid of subtly shifting, small black-and-white triangles is interrupted by a white V-shaped blurring in the bottom half of the painting. The result is an image that, while ostensibly static, seems to flicker with the intensity of flames. With Interrupted Circle (1963), which is part of Riley’s ‘disfigured circle’ series, the artist plays with the illusion of sections of the circle moving outwards, as if they’re in the process of being pulled into another dimension. She went a step further with Climax (1963), shaping the canvas itself with lyrical curves. (It’s one of only three shaped works Riley made, all between 1963 and 1964.) In Serif (1964) undulating lines shift the canvas sideways from its more familiar orientation – it points upwards, like a diamond. The effect is like peering through a porthole and glimpsing a landscape speeding by.

The works’ genesis might seem at odds with the lyricism of Riley’s early palette. On a summer’s day in 1960, the 29-year-old painter was driving through the hills of Tuscany in Italy with the artist and writer Maurice de Sausmarez. Having studied art at Goldsmiths and the Royal College of Art in the early 1950s, she had been working as a graphic designer with the advertising agency J. Walter Thompson, when she met de Sausmarez at the summer school he ran. This early mentor who opened her eyes to the significance of the Post-Impressionists, became her lover. Suddenly, thunder clouds began rolling in and the landscape shimmered in the heat. Riley, fascinated, made numerous sketches.

Back in her London studio, she painted Pink Landscape (1960), a square, violet-pink-and-blue pointillist work, which is clearly in thrall to the artist’s hero, Georges Seurat. (The previous year, she had recreated his painting Bridge at Courbevoie (1886-1887), a process that helped her understand how juxtaposing separate colors can change perception.) And yet, despite the painting’s condensed beauty, Riley was dissatisfied with her inability to capture what she had witnessed on that hot Tuscan day. When I visited her in her London studio eight years ago, she dismissed the painting as ‘a most useful failure.’ It was not necessarily a bad thing. In her 1996 essay ‘Painting Now’, Riley explained: ‘Painting without its problems can no longer be painting. It depends upon them for its existence.’

Riley is an artist who has always made clear that in order to understand the language of art, you need to first dive into its history, and her many essays give clear insight into her thinking. While her work is emblematic of 1960s visual culture, made famous by the reproduction of its ‘trippy’ effects on t-shirts or Biba dresses, its dilution in popular culture infuriated her. While being driven to the airport following her breakout inclusion in ‘The Responsive Eye’, at MoMA, New York, in 1965, she was outraged to see her paintings had been reproduced without permission on the dresses that filled Madison Avenue’s shop windows. In fact, she was first drawn to Geometric Abstraction because of its mythic familiarity: squares, triangles, and rectangles are ancient forms, whose function is at once versatile and universal. Also, like Paul Cézanne, she’s long been indebted to the lessons – both visual and conceptual – she can learn from the landscape. In 1973, in ‘Working with Nature’, she wrote that ‘I draw from nature, I work with nature, although in completely new terms.’

Back in the early 1960s, thinking about two Futurist exhibitions she had visited in Venice and Milan, and also the Lascaux cave paintings (which she described to me as ‘a kind of very vivid Cubism’), she realized that she had, until that point, been pursuing ‘the wrong goal’ in her attempts at capturing what she had seen on that summer’s day in Italy. She decided that an accurate representation of a landscape needed what she terms ‘a kind of equivalence’: to evoke sensation as well as optical reality. She also came to believe that ‘the great paintings are the clearest; they have been made by those who made the greatest effort to overcome confusion and to arrive at clarity.’

The result was Movement in Squares (1961), a painting the writer Michael Bracewell, who has worked closely with Riley for decades, describes as being ‘as shocking in its modernity as it is enchanting in its aesthetic resolution.’ It could not be more different from Pink Landscape – and yet, is its logical heir. Twelve rows of black-and-white squares pulse, fade, and swell; looking at them is as much a bodily sensation as an optical one.

Movement in Squares, though, wasn’t the first of Riley’s black-and-white pictures. That honor goes to Kiss (1961): a monumentally austere image of a rounded, weighty black shape that is almost, but not quite, touching a black, geometric base. Writing in 2008, Bracewell, noted that they were ‘made in response to the end of an unhappy relationship.’ The artist and de Sausmarez had parted ways. She produced what she thought would be a goodbye to him and her work as a painter. Instead, it was a beginning. In her essay ‘The Experience of Painting’ she wrote: ‘People at the time thought, and some people still seem to think, that they were paintings having to do with optical experiment…really they were an attempt to say something about stabilities and instabilities, certainties and uncertainties.’ In her ‘Statement’ of 1970, she declared, ‘My paintings are, of course, concerned with generating visual sensations but certainly not to the exclusion of emotion. One of my aims is that these two responses shall be experienced as one and the same.’

Riley’s experiments – a fusion of optical and emotional exploration – resulted in a visual language that, despite its hard-edged clarity, is essentially ambiguous: She has written that the act of painting is the act of translating ‘a text unknown even to yourself.’ To repeat a motif is not a sign of reduction or detachment: quite the opposite. She believes that ‘repetition, contrast, calculated reversal and counterpoint also parallel the basis of our emotional structure,’ thoughts recorded in 1965 while she was making her black-and-white work, in the essay ‘Perception is the Medium’. In many of her interviews, Riley reiterates that the act of looking involves all the senses. In 1967, the art historian David Sylvester asked her what looking at her paintings was comparable to. She replied: ‘Running…early morning…cold water…fresh things, slightly astringent…things like this…certain acid sort of smells.’ Life, for Bridget Riley, is not outside the picture frame: it inhabits it.