Her first novel was a bestseller, and was adapted into the double-Oscar-winning film Precious. Her second, The Kid, has just been published to enthusiastic reviews. But author and poet Sapphire says that, as an African-American artist, she nonetheless feels the "very real and very painful" effects of racism.

Speaking at the Edinburgh international book festival, Sapphire said that when Push – the novel that became the film Precious – was published, readers found it difficult to grasp that she, the author, was separate from its impoverished, abused, illiterate narrator.

"I remember when Push came out, there was shock when people saw me – they'd say: 'You're not 16, you're not obese. We thought this was your life story.'

"It was as though they thought this was some illiterate teenager's life story and I had spoken it into a tape recorder, and some white editor had written it."

She said: "It's as if black artists are only able to tell autobiographical horror stories and don't have an imagination. There was an idea I wouldn't have been able to conceive of [the narrator] Precious's life unless I had lived it; there's an idea I wouldn't have the ability to write about a young African-American male without somehow living as a male. But the idea that I could not read and study and use my imagination and create and craft a character has been very real and very painful to me."

Sapphire, 61, was born in California and came to literary prominence as a performance poet. She gleaned some of her material for Push (1996) as a teacher in New York. Her second novel, The Kid, imagines the life of Precious's son Abdul, who is orphaned at nine when his mother dies from an Aids-related illness. He is abused at the Catholic school he attends; becomes an abuser himself; and later achieves success as a dancer in an avant-garde, downtown New York company. She described the story as "an African-American Oliver Twist".

Academic and creative achievement are still regarded as beyond the capabilities of black people in America, she said. "That whole realm of intellectual activity and artistic activity is not seen as something that black people do. We're still the dancer not the choreographer, and still the musician, not the conductor. It's still harder for us to get into the whole realm in the arts."

She talked of her frustration that in the US, her novels end up in the "African-American literature" section of bookshops. "I just don't understand why the literature is still being categorised, why Toni Morrison and James Baldwin are in a certain section, instead of just in the 'literature' section," she said.

"That's not something that Stephen King is going to go through. Philip Roth is not going to walk into a bookstore and see his work in the 'Jewish Male' section. It's absurd. But that is what I have to go through; and I want them to sell my books so I have to be nice. I say: 'I'll sign some copies if you take the book and put in on the table: if you let my little kid out of the ghetto.'"

In the book Abdul gradually enters the liberal world of New York artists and creatives. But this is no paradise: he becomes the victim of a subtle but insidious racism. According to Sapphire, "while we see with total impunity the appropriation of our artforms by other ethnic groups, what we see here is that, as Abdul tries to enter into the white avant-garde scene of dance, they are not so quick to let him in as young white people are to play the blues or appropriate black culture. Here, when he tries to enter this this Merce Cunningham-type world they are very chary of letting him in." In this way, said Sapphire, "We have the chance to look at the racism of that downtown, avant-garde set."

She spoke of her delight at the film adaptation of Push, which, under the title of Precious, won Oscars for best screenplay and best supporting actress. But just as she held out for a decade before agreeing to the adaptation of her first book, she was in no hurry to see The Kid made into a film. "I don't write to placate publishers' economic ideas," she said.