Watch someone lift a box and you can tell whether the box is heavy or light. Watching the way someone moves you can often tell whether they're a man or a woman. But what kind of information does the brain needand what processes does it go throughto convert a view of something into knowledge about that thing?
Psychologist Gunner Johansen
A number of decades ago, psychologists worked with photographs or drawings of people doing various activities. By showing people a variety of these pictures and asking them to describe what they saw, psychologists believed they could learn how the brain interpreted visual images.
In a doctoral thesis in 1950, Swedish psychologist Gunner Johansen argued that to understand how the brain interprets motion, scientists needed to focus on the motion itself. To do that, he taped twelve Christmas-tree lights to a volunteerone at each major jointthen filmed the volunteer walking in the dark so that only the lights showed up on the film.
When the lights were still, people watching the film had no idea what they were looking at. But as soon as the lights moved it became obvious that the lights represented a person. Most of the time they could even tell the person's sex.
Since then researchers have done similar experiments in which people wearing lights lift objects. Volunteers watching the film have been able to guess the weight of the objects with surprising accuracy.
Johansen's experiments with Christmas-tree lights showed that we interpret the world around us more by the way it moves than by the way it would look if it all stood still.