|In the 1922 poem The Waste Land, T. S. Eliot writes, cryptically:
- Who is the third who always walks beside you? /
- When I count, there are only you and I together /
- But when I look ahead up the white road /
- There is always another one walking beside you.
In his footnotes to this verse, Eliot explained that the lines “were stimulated by the account of one of the Antarctic expeditions [Ernest Shackleton’s] …that the party of explorers, at the extremity of their strength, had the constant delusion that there was one more member than could actually be counted.”
Whatever the immediate cause of the sensed-presence effect, the deeper cause is to be found in the brain. Michael Shermer then proposes 4 possible explanations for this effect – excerpted below from his Scientific American column
- The hallucination may be an extension of the normal sensed presence we experience of real people around us, perhaps triggered by isolation.
- During oxygen deprivation, sleep deprivation or exhaustion, the rational cortical control over emotions shuts down, as in the fight-or-flight response, enabling inner voices and imaginary companions to arise.
- The body schema, or our physical sense of self – believed to be located primarily in the temporal lobe of the left hemisphere – is the image of the body that the brain has constructed. If for any reason your brain is tricked into thinking that there is another you, it constructs a plausible explanation that this other you is actually another person – a sensed presence – nearby.
- The mind schema, or our psychological sense of self, coordinates the many independent neural networks that simultaneously work away at problems in daily living so that we feel like a single mind.