I became aware of my guide, who was shrouded in a black monk's cowl, an hour or so after I lost my bearings and realized I was lost. He — I'm sure it was a "he," although I never saw his face — walked about 20 feet to my right and just slightly ahead of me, subtly indicating the way I should take. He arrived from nowhere, and disappeared into nowhere at dusk, about the time I saw a road (and safety) at the edge of the forest I'd been walking through all day. Half a century later, I can still clearly see my spirit guide in my mind's eye.

As a 19-year-old student wandering alone and lost through remote woods in northern Finland in 1962 (it's a long story), I wonder now about my lack of wonderment! Why didn't I speak to him? How was it possible that I just accepted this benign apparition and unquestioningly trusted his sense of direction? I didn't tell many people about this episode for fear they'd think me crazy.

I needn't have worried. Turns out most of us have experienced something of the kind at one time or another. For instance, a 1983 study by researchers at Murray State University in Kentucky found that 57 percent of healthy volunteers had heard their name spoken by an invisible presence, while the sort of visual illusion that I'd experienced is so common among isolated sailors, mountain climbers, polar explorers, Iditarod competitors and cross-country cyclists that it's been given a name: the third-man factor.

Tales of auditory and visual hallucinations go back a long way, from Athena placating Achilles' wrath in the Iliad, to God staying Abraham's hand as he was about to sacrifice his son Isaac, and from Joan of Arc taking the counsel of Saint Michael to my beloved Aunt Dorothy, whose life changed the day she heard a divinity say her name in an otherwise empty house.

For better or for worse, science has tried to explain our voices and apparitions. Perhaps they result from a competition between the "controlled" brain processes in the prefrontal cortex and the automatic processes in the occipital (rear) cortex, especially when we're under stress. Or maybe our normal body schema, our physical sense of self, sometimes gets confused into thinking that another self, a doppelganger, is present, so our brain creates a more plausible explanation — another person — to maintain its sanity.

Or my favorite proposal: At times of stress (and regularly in the case of many schizophrenic and epileptic patients) our brains revert to their ancient split state, or bicamerality. In his only book, The Origin of Consciousness in the Breakdown of the Bicameral Mind, the late Julian Jaynes, professor of psychology at Princeton, claimed that we were all once "floridly hallucinatory." Citing evidence from the 3,000-year-old Iliad and other old works, Jaynes asserted that everyone heard voices back then, as the right hemisphere of the brain "spoke" to the left hemisphere, before cultural changes caused the brain to "mend" (Field Notes, March 4, 2010).

Heard any voices lately? Don't worry, you're not crazy. More likely, your brain is doing just what it needs to do to convince itself that it's perfectly sane. Well, as sane as any of us are, anyway.

Barry Evans ([email protected]) regrets not taking a photograph of his spirit guide, to prove his story to skeptics.