Motion Blindness

Now here is a medical case that illustrates just how 'strange' the human visual system is:

The patient had great difficulty pouring coffee into a cup. She could clearly see the cup's shape, color, and position on the table, she told her doctor. She was able to pour the coffee from the pot.

But the column of fluid flowing from the spout appeared frozen, like a waterfall turned to ice. She could not see its motion. So the coffee would rise in the cup and spill over the sides.

More dangerous problems arose when she went outdoors. She could not cross a street, for instance, because the motion of cars was invisible to her: a car was up the street and then upon her, without ever seeming to occupy the intervening space.

Even people milling through a room made her feel very uneasy, she complained to Josef Zihl, a neuropsychologist who saw her at the Max Planck Institute for Psychiatry in Munich, Germany, in 1980, because "the people were suddenly here or there but I did not see them moving."

The woman's rare motion blindness resulted from a stroke that damaged selected areas of her brain.

I came across this on the Howard Hughes Medical Institute site. The article goes on to talk about how the visual systems of other species are different. For instance, humans detect motion with their brains while simple vertibrates, such as frogs, do it with their retinas instead (I didn't know that).

Pretty cool stuff. I recommend reading the whole article. By the way, the site also has several more interesting pages on sight and hearing.