Sir Anthony Hopkins heard them. So did Martin Luther King, Carl Jung, Sigmund Freud, Mahatma Gandhi, Joan of Arc and Socrates.
These well-known identities have all reported hearing voices - a phenomenon which is reasonably common, with 4-10 per cent of the population admitting to it.
It is an accepted fact of life among various indigenous groups, including North American Indians and Aboriginals, and its prevalence worldwide prompted the establishment late last century of a Hearing Voices Network.
People who experience it are called voice hearers by the hearing voices movement, although many may also have visual, smelling, feeling and other sensations.
In psychiatry, people who are disturbed by voices are described as having auditory hallucinations and those who have visions as having visual hallucinations. They may be diagnosed with schizophrenia.
The Hearing Voices Network was introduced in Australia in 2005 by the Richmond Fellowship of WA (RFWA).
According to Hearing Voices Network Australia (HVNA), taking into account all voice-hearing experiences, only a small number of voice hearers experience distressing, debilitating voices, with others describing it as a positive spiritual, cultural, psychic or everyday experience. Voices can be male, female, familiar, unfamiliar, friendly, helpful, angry, cruel, commanding, highly critical or undermining. They can be sounds, music, chanting or shuffling. They can stop for years and then return.
Joe Calleja, chief executive of the RFWA, said research shows that a lot of distressing voice hearing results from early childhood trauma, including sexual and physical abuse, or emotional trauma such as bullying, neglect, abandonment or the sudden death of a loved one. In one well-documented case, a man used to hear the voice of a priest who had sexually abused him.
RFWA and the HVNA offer training to professionals as well as voice hearers and their family and friends. The voice hearers can be helped to learn how to cope with the problem.
"People feel for the first time as though they can have discussions about their voices without the fear of being judged 'mad'," Mr Calleja said.
"When people learn skills to control their voices, their quality of life and mental health is improved, often hospitalisations are reduced or even eliminated, levels of depression are reduced and suicidal ideation diminishes. Then people can get control over their lives, get jobs, establish relationships."
For some people labelled "treatment resistant", medication does not necessarily help and in some instances contributes to other voices emerging.
In an Irish study reported in the British Journal of Psychiatry in April, more than one in five children aged 11 to 13 reported hearing voices. While just over half of these were found to have a non-psychotic psychiatric disorder such as depression, the other half did not have any underlying problem.
Mr Calleja said the way children were dealt with if they heard voices often completely missed their needs and compounded their distress.
HVNA manager Lyn Mahboub said children often explained their voices as those of "imaginary friends", which could be quite a normal experience and did not necessarily lead to distressing voice hearing.
"It is not scientific and there isn't a blood test to find out (what is going on) and so what people go on are self or other reports," she said.
In studies by Dutch researcher Sandra Escher, it was shown that children distressed by their voices could be helped, largely when parents and others supported them to deal with any current life problems they might be experiencing.
The three phases of voice-hearing recovery are described as startling, organisational and stabilisation - the stage at which the person has learnt to understand, organise and cope with their voices.
RFWA has received funding from Lotterywest to start up Voices@Work, which helps people who hear voices to get or stay in a job.
"A lot of people are not going anywhere near employment because of the stigma associated with their problem and the distress associated with their voices," Mr Calleja said.
RFWA has worked with about 25 people who are voice hearers and supported them to the point where they are significantly more prepared to seek work because their confidence has built up.
"Here is a group in our community that is completely invisible or, if they are visible, they are seen as really crazy, very sick people who are written off," Mr Calleja said.
"In fact, many of them can be given the opportunity to live a productive life in the community."
Voices@Work project worker Amanda Olsen said that by sharing her own voice- hearing experience, she was able to assist others and give them hope that they could one day gain the employment they wanted.
RFWA/HVNA run a two-day training course every month on the hearing-voices recovery approach as well as three-hour Snapshots on the Hearing Voices Approach. They have been attended by mental health workers, psychiatrists, nurses and others. RFWA/HVNA also offer free family information evenings.
The website for RFWA is rfwa.org.au and for HVNA is hvna.net.au. The phone number for both is 9350 8800. If you or someone you know is thinking about suicide, phone Lifeline on 13 11 14.