Editor's Note: Tanya Marie (“T.M.”) Luhrmann is a psychological anthropologist and the Watkins University professor in the department of anthropology at Stanford University in Stanford, California. She is the author of "When God Talks Back: Understanding the American Evangelical Relationship with God."

By T.M. Luhrmann, Special to CNN

(CNN)—In the Bible, God spoke directly to Abraham. He spoke directly to Moses. He spoke directly to Job. But to your neighbor down the street?

Most people reading the ancient scriptures understand these accounts of hearing God’s voice as miracles that really did happen but no longer take place today, or maybe as folkloric flourishes to ancient stories. Even Christians who believe that miracles can be an everyday affair can hesitate when someone tells them they heard God speak audibly. There’s an old joke: When you talk to God, we call it prayer, but when God talks to you, we call it schizophrenia.

Except that usually it’s not.

Hearing a voice when alone, or seeing something no one else can see, is pretty common. At least one in 10 people will say they’ve had such an experience if you ask them bluntly. About four in 10 say they have unusual perceptual experiences between sleep and awareness if you interview them about their sleeping habits.

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And if you ask them in a way that allows them to admit they made a mistake, the rate climbs even higher. By contrast, schizophrenia, the most debilitating of all mental disorders, is pretty rare. Only about one in 100 people can be diagnosed with the disorder.

Moreover, the patterns are quite distinct. People with schizophrenia who hear voices hear them frequently. They often hear them throughout the day, sometimes like a rain of sound, or a relentless hammer. They hear not only sentences, but paragraphs: words upon words upon words. What the voices say is horrid—insults, sneers and contemptuous jibes. “Dirty. You’re dirty.” “Stupid slut.” “You should’ve gone under the bus, not into it.”

That was not what Abraham, Moses and Job experienced, even when God was at his most fierce.

For the last 10 years, I have been doing anthropological and psychological research among experientially oriented evangelicals, the sort of people who seek a personal relationship with God and who expect that God will talk back. For most of them, most of the time, God talks back in a quiet voice they hear inside their minds, or through images that come to mind during prayer. But many of them also reported sensory experiences of God. They say God touched their shoulder, or that he spoke up from the back seat and said, in a way they heard with their ears, that he loved them. Indeed, in 1999, Gallup reported that 23% of all Americans had heard a voice or seen a vision in response to prayer.

These experiences were brief: at the most, a few words or short sentences. They were rare. Those who reported them reported no more than a few of them, if that. These experiences were not distressing, although they were often disconcerting and always startling. On the contrary, these experiences often made people feel more intimate with God, and more deeply loved.

In fact, my research has found that these unusual sensory experiences are more common among those who pray in a way that uses the imagination—for example, when prayer involves talking to God in your mind. The unusual sensory experiences were not, in general, associated with mental illness (we checked).

They were more common among those who felt comfortable getting caught up in their imaginations. They were also more common among those who prayed for longer periods. Prayer involves paying attention to words and images in the mind, and giving them significance. There is something about the skilled practice of paying attention to the mind in this way that shifts—just a little bit—the way we judge what is real.

Yet even many of these Christians, who wanted so badly to have a back-and-forth relationship with God, were a little hesitant to talk about hearing God speak with their ears. For all the biblical examples of hearing God speak audibly, they doubt. Augustine reports that when he was in extremis, sobbing at the foot of that fig tree, he heard a voice say, “Take it and read.” He picked up the scripture and converted. When the Christians I know heard God speak audibly, it often flitted across their minds that they were crazy.

In his new book, "Hallucinations," the noted neurologist Oliver Sacks tells his own story about a hallucinatory experience that changed his life. He took a hearty dose of methamphetamines as a young doctor, and settled down with a 19th century book on migraines. He loved the book, with its detailed observation and its humanity. He wanted more. As he was casting around in his mind for someone who could write more that he could read, a loud internal voice told him “You silly bugger” that it was he. So he began to write. He never took drugs again.

Now, Sacks does not recommend that anyone take drugs like that. He thinks that what he did was dangerous and he thinks he was lucky to have survived.

What interests me, however, is that he allowed himself to trust the voice because the voice was good. There’s a distinction between voices associated with psychiatric illness (often bad) and those (often good) that are found in the so-called normal population. There’s another distinction between those who choose to listen to a voice, if the advice it gives is good, and those who do not. When people like Sacks hear a voice that gives them good advice, the experience can transform them.

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This is important, because often, when voices are discussed in the media or around the kitchen table, the voices are treated unequivocally as symptoms of madness. And of course, voice-hearing is associated with psychiatric illness.

But not all the time. In fact, not most of the time.

About a third of the people I interviewed carefully at the church where I did research reported an unusual sensory experience they associated with God. While they found these experiences startling, they also found them deeply reassuring.

Science cannot tell us whether God generated the voice that Abraham or Augustine heard. But it can tell us that many of these events are normal, part of the fabric of human perception. History tells us that those experiences enable people to choose paths they should choose, but for various reasons they hesitate to choose.

When the Rev. Martin Luther King Jr. sat at his kitchen table, in the winter of 1956, terrified by the fear of what might happen to him and his family during the Montgomery bus boycott, he said he heard the voice of Jesus promising, “I will be with you.” He went forward.

Voices may form part of human suffering. They also may inspire human greatness.

The opinions expressed in this commentary are solely those of TM Luhrmann.