How can pain impact our tolerance?

Sensation and perception:

What is the difference between sensation and perception?  Oliver Sacks is a well known author and doctor who has published books involving case studies from his practice.  One such book, An Anthropologist on Mars, depicts the story of a client who lost his vision shortly after birth, and then regained it through surgery at a much later time in life.  There was a movie later made, At First Sight, that depicted this story.  Virgil who regained his sight after surgery, had a difficult time identifying objects that he was seeing, how to navigate and use his depth perception and overall how to function.  He had to spend a great deal of time learning what he was seeing as he transposed his original way of seeing via his senses through a connection with his visual interpretation.  Why did this happen?  What is sight?  Why was he having issues with perception of motion, depth perception, motion parallax, perceptual constancies?

Physiological Pain

Research into the experience of pain is a rapidly expanding field. Why can some people tolerate great amounts of pain while others can tolerate no pain at all? What causes pain and how can it be adaptive? How does our perception and emotional interpretation of pain impact our tolerance?