… whilst part of what we perceive comes through our senses from the object before us, another part (and it may be the larger part) always comes out of our head.
(William James, 1890)
In 1959 a Canadian psychologist, Robert Sommer, described an incident leading to a trial at which he was a juror. Here is Sommer's account of the incident:
A hunting party went out one afternoon looking for deer. While driving through a field, their car became stuck in the snow and eventually the transmission broke. Of the five men in the party, two volunteered to go to a nearby farmhouse for help. Of the remaining three, one remained in the rear seat while the other two stood at the front of the car. Meanwhile, one of the two men on the way to the farmhouse decided that there was no reason for both of them to go, and he thought he might be able to scare up a deer. Unknown to the men in the car, he circled around down a hill in front of them. At that point, one of the men standing outside the car said to the other, 'That's a deer, isn't it?', to which the other replied in the affirmative. The first then took a shot at the deer. The deer pitched forward and uttered a cry, which both men heard as the cry of a wounded deer. When the deer started running again, the second man implored, 'Don't let him get away, please get him for me'. The first man fired again and the deer went down but continued its forward movement. A third shot brought the deer to the ground and both men started running towards it. By this time the third man in the car, who had been trying to find and focus his field glasses, suddenly called out, 'It's a man'.
The ideas in this chapter attempt to explain what happened on that tragic afternoon.
After that real-life story, consider two simple demonstrations. Look first