That's part is from the "Believing Brain" by Michael Shermer
Quote:
1. An extension of our normal sense of presence of ourselves and others in our physical and social environments.
This process of sensing a presence is probably just an extension of our normal expectations of others around us because we are such a social species. We have all lived with others, particularly in our formative childhood and teenage years, and we develop a sense of their presence whether they are there or not. Under normal conditions, you come home from school or work expecting your fellow family members to either be home or to arrive soon. You scan for telltale cues of cars or keys or coats. You listen for their familiar sounds of welcome.
Their presence is either sensed or anticipated. For years after my mother died, whenever I visited my father at the home where I grew up I had this overwhelming feeling that she would come around the corner at any moment, even though my rational brain kept correcting my emotional expectations. For eight years after my mother’s passing my stepfather kept close company with his demonstrative black Lab Hudson, and whenever I stopped by the house Hud would always come running to greet me; even after he was gone I still felt like he’d come running to the door. So ingrained are these sensed-presence expectations that even years later, whenever I was in my ancestral home, I had the eerie feeling that my stepdad and I were not alone.
This was the first point explaining why people feel presences....