The recording of the song you will most often hear these days is an instrumental version complete with lush strings, a backing choir and a gently soaring saxophone solo that rises up out of the brass section.
But in 1966 when Burt Bacharach penned "Nikki" for his prematurely born daughter, there were accompanying lyrics courtesy of his long-time writing partner, Hal David, that spoke of good times and bad: "Nikki, where can you be? It's you, no one but you for me. I've been so lonely since you went away. I won't spend a happy day till you're back in my arms."
Now, four decades after she was born and after that piece of music was written for her, Lea Nikki Bacharach has been swallowed up by the bad times. Having struggled all her life with the developmental disorder Asperger's syndrome (AS) - a form of autism - the young woman known as Nikki took her own life last week. Her body was found in her California home.
Officials from the Ventura County coroner's office said she had suffocated herself using a plastic bag and helium gas.
A brief statement issued by Bacharach and Nikki's mother - his former wife Angie Dickinson, an actress - said their only daughter killed herself at her apartment in the suburb of Thousand Oaks, north of Los Angeles, at about 8pm last Thursday.
"She quietly and peacefully committed suicide to escape the ravages to her brain brought on by Asperger's," it read. "She loved kitties, and earthquakes, glacial calving, meteor showers, science, blue skies and sunsets, and Tahiti. She was one of the most beautiful creatures created on this earth, and she is now in the white light, at peace."
Now 78, Bacharach is still going strong. Last year he recorded a jazz album with the Dutch singer Trijntje Oosterhuis, featuring a number of his classic songs. He played piano on several tracks. The man who for years was known for his work with Dionne Warwick was recently forced to postpone a tour of Australia and New Zealand after injuring his shoulder.
Aside from the personal tragedy this has brought for the man who has written more than 50 top 40 hits including "Walk on By" and "The Look of Love" the suicide of the 40-year-old woman has focused attention on AS, an often misunderstood condition that, like all forms of autism, leaves sufferers struggling with communication, social interaction and imagination. At the same time, people with AS can be high achievers. A number of celebrities have been diagnosed with the disorder.
"Autism is a spectrum disorder and it affects people in very different ways," a spokeswoman for the UK-based National Autism Society (NAS) said.
"You can have classic autism at one end, where people are very clearly affected and may not be able to communicate verbally.... As you move up the spectrum you have high-functioning autism or AS. People with AS usually have a normal IQ but have problems expressing themselves.
"People with AS can lead a very full life - they can be married and have a job. But the right support is needed and [there needs to be] understanding by people such as GPs or social services so that needs can be fully met. It's important that people get support when they need it."
AS was first identified by the late Austrian physician Hans Asperger in the 1940s. In a paper written in 1944 he talked of a pattern of behaviour he had identified in four young boys which he termed "autistic psychopathy". He said this behaviour featured "a lack of empathy, little ability to form friendships, one-sided conversation, intense absorption in a special interest, and clumsy movements". He referred to children with AS as "little professors" because of their ability to talk about their favourite subject in great detail.
He wrote: "Exceptional human beings must be given exceptional educational treatment, treatment which takes into account their special difficulties. Further, we can show that despite abnormality, human beings can fulfil their social role within the community, especially if they find understanding, love and guidance."
Named in recognition of Asperger's work, the condition was formally recognised in the US in 1994 when it was included in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders. In the UK, it was little-known until the work of Lorna Wing, a founder member of the NAS, and currently a consultant, who wrote about it in 1981. Her interest was sparked by the birth of a daughter who was diagnosed with the condition.
Since then there has been a fresh drive into learning more about AS. There have also been claims that a number of brilliant historical figures, including Sir Isaac Newton and Albert Einstein, may have had the condition. In 2003, New Scientist magazine reported that the Cambridge-based autism expert Simon Baron-Cohen had analysed the behaviour of the two men and concluded they may have shown typical symptoms.
It said Newton seemed to have been a classic case. "He hardly spoke, was so engrossed in his work that he often forgot to eat, and was lukewarm or bad-tempered with the few friends he had. If no one turned up to his lectures, he gave them anyway, talking to an empty room. He had a nervous breakdown at 50, brought on by depression and paranoia." Meanwhile, as a child Einstein was a loner, and repeated sentences obsessively until he was seven.
Professor Baron-Cohen concluded: "Passion, falling in love and standing up for justice are all perfectly compatible with Asperger's syndrome. What most people with AS find difficult is casual chatting - they can't do small talk." He added: "This condition can make people depressed or suicidal, so if we can find out how to make things easier for them, that's worthwhile."
What causes autism and AS is still unclear. Experts believe a number of factors may be involved, of which genetics may be just one. They also believe that if there is an "autism gene" it is more likely to involve a number of genes rather than one. The NAS says: "The difficulty of establishing gene involvement is compounded by the interaction of genes and by their interaction with environmental factors."
While there is no known cure for autism, there are therapies that doctors use. There are also an increasingly vocal number of activists who believe society should celebrate the differences of people with autism. The Autism Liberation Front, a group founded in the US but with supporters in the UK where about 530,000 people have autism, sells badges with the slogan: "I am not a puzzle, I am a person."
Another group, Aspies for Freedom, says AS and autism are "not negative and not always a disability". Elsewhere, experts say people with AS can often learn tips about improving their social interaction that most people learn largely automatically.
In 2001 the electronic pop pioneer Gary Numan claimed that his difficulty in social situations had led him to believe he had AS. He said: "Polite conversation has never been one of my strong points. Just recently I actually found out that I'd got a mild form of Asperger's syndrome which basically means I have trouble interacting with people. For years, I couldn't understand why people thought I was arrogant, but now it all makes more sense."
Does AS or autism make a person more likely to commit suicide, as in the case of Burt Bacharach's daughter? The NAS spokeswoman said it was difficult to answer because the disorder affected people in different ways. "It's not a mental disorder, it's a developmental disability. It is not a mental health issue per se," she said.
But Dr Wing and others have highlighted issues of psychiatric trauma and varying degrees of depression among young adults with AS, something that seems related to their awareness of their difference from others. One paper on the subject claims that five out of 22 young adults with AS had tried to take their lives.
Bacharach's daughter was born a year after he and Dickinson were married. In their statement, the former couple said their daughter had "lived a happy life in and around Beverly Hills". She had studied geology at California Lutheran University but poor eyesight had prevented her from pursuing a career in it.
Since Nikki's death was announced, internet forums have been filled with condolences for Bacharach. Andre B wrote on the fans' website, A House Is Not A Homepage, that he had met Nikki and her mother three years ago at a party celebrating the birthday of the science fiction writer Ray Bradbury. "She was a big fan of astronomy, and loved looking through telescopes," he wrote. "I brought a telescope to Ray's party and showed her and Angie Mars and the Andromeda galaxy. Nikki was fascinated. She had a genuine, child-like sense of wonder about the sky. Angie couldn't have been sweeter or more gracious. I'll never forget that night. This is really sad news."
Asperger's Syndrome: Famous sufferers
Asperger's was not fully recognised as a syndrome until the early Nineties. But psychologists suggest Albert Einstein, Vincent Van Gogh, Stanley Kubrick and Jane Austen may all have been affected by the syndrome.
* GARY NUMAN
Numan was diagnosed with Asperger's in 2001, 15 years after releasing the top 10 hit "Cars". "For years, I couldn't understand why people thought I was arrogant, but now it all makes a bit more sense," he said.
* SATOSHI TAJIRI
Tajiri, the creator of Pokemon, has been diagnosed with Asperger's syndrome. He has been described by Nintendo officials as incredibly creative but "reclusive" and "eccentric," characteristics consistent with Asperger's.
* DAVID BELLAMY
The naturalist and TV presenter Bellamy mentions in his autobiography that, although undiagnosed, he believes he has a form of autism which may be Asperger's.
* VERNON SMITH
The Nobel-prize winning economist has spoken out about the creative benefits of Asperger's. "I can switch out and go into a concentrated mode and the world is completely shut out," he said in a recent interview. "If I'm writing something, nothing else exists."