between the leash and the dog's collar is stronger than the child's
grip on the leash, and the man is knocked aside because both he
and the dog are solid objects that collide when their trajectories
cross. This kind of phenomenon is automatically represented in
our minds by a set of mechanisms that do what psychologists call
"intuitive physics," in analogy with scientific physics.
- Understanding physical causation: In the scene you witnessed, you
saw the dog hit the man on its way and you then saw the man
stumble and fall down. But that is not the way you would describe
it. What seems to have happened is that the man tripped becausehe
had been hit by the charging dog. Physical events around us are [97]
not just one damn thing after another; there often appear to be
causes and effects. But you cannot seea cause, at least literally.
What you see are events and your brain interpretstheir succession
as cause plus effect.
- Detecting goal-directed motion: The dog charged across the street in
a particular direction that happened to point toward the cat's
location. To put things in a more natural way, the dog's goalwas to
get closer to the cat. If all you saw was physical motion, you would
think that some invisible force was driving the dog toward the cat.
But an inference system in your mind suggests that this invisible
force is inside the dog's head, in his desire to get closer to
something that looks like prey.
- Keeping track of who's who: The scene makes sense to you as an
eyewitness only if you can track the different characters and keep a
particular "file" on each of them with an account of what just
happened to them or what they just did. This seems of course
trivially easy, if some system in your brain takes a snapshot of every
character's face, and then manages to reidentify the different
characters, even though faces and bodies change orientation, they
are partly occluded, the lighting is different, etc.
- Linking structure to function: The screwdriver hurt the man as he
fell down. This is not too surprising as this instrument was
probably hard, pointed and the blade at the end was probably
sharp. We intuitively guess all this, not just because screwdrivers in
general are like that but also because there is a reason for these
features: they help in performing particular functions. That we
expect tools to have such functional features is manifest in the
surprise that would be created if the crowbar or screwdriver
happened to be soft as rubber.
THEKIND OF MINDITTAKES
