Here is an interesting excerpt from the feature by Alasdair McGregor in the Sept 20 Australian Geographic:

Since the syndrome was first clinically documented in the 1940s, psychologists have postulated various triggers and explanations ranging from sensory deprivation, extreme fatigue and boredom, to an evolutionary adaptation. If one person can summon up a benevolent presence while others are incapable of such a thing, then the psychological comfort may give a boost in the survival stakes.

Sydney-based clinical psychologist Dr Lissa Johnson has successfully encouraged trauma victims to "cultivate inner characters", lending imagined support and comfort through internal dialogue in times of need. She says she finds it "very powerful in therapy", but also sees a parallel with the third man syndrome, where the "psyche could rise to the occasion and fulfil a need for external assistance". Instead of talking to oneself, Dr Johnson believes, "imagery is emotionally more powerful than language".    

For the full article click HERE

Or cut and paste this:

http://www.australiangeographic.com.au/journal/an-adventurers-guardian-angel-the-voice-within.htm