Cats love laser pointers. That little moving dot of light is about as much fun as a dangling string. Although it is funny to watch a cat chase a laser pointer around the room, humans are no better than cats when it comes to moving dots. Just like cats, we see some forms of movements by little dots as signs of life. Sometimes we see human motion, motivation, and emotion in the movements of inanimate shapes. The single leaf fluttering down on a breeze can confuse us - is it a butterfly, a bird? (There are, by the way, great YouTube videos of cats chasing laser pointers, including: Cat and Laser light.)
In the last decade, several researchers have clarified what about motion leads to claims of animacy, claims that the movement is life-like. For example, Tremoulet and Feldman (2000; 2006) found that movement change is a critical component - the more the dot changes direction and speed, the more people attribute animacy to it. Cats chase the laser pointer's dot of light because it changes direction and speed. Cats see the moving dot as alive and worth catching. Maybe they think it would taste good if they could just catch it.
Last fall, Pratt, Radulescu, Guo, and Abrams (2010) found that these biological motions grab your attention, even if you don't realize what's happening. In a very clever experiment, they had people watch a display of moving dots and report when one of the dots disappeared. For the most part, the dots followed simple laws of physics and displayed no signs of life - just bouncing of the walls and each other. But in rare instances one of the dots would change motion and speed without running into anything - evidence of the dot being alive! If that dot disappeared, people noticed it more quickly than other dots disappearing. Something about the life-like motion captured their attention. The really cool part is that the observers never became aware that there were occasional life-like motions. Moving dots can be perceived as being alive and animate motion grabs your attention.
Of course, researchers haven't only been concerned with animate motion by single dots. Using motion, Gao, McCarthy, and Scholl (2010) created a wolf pack of triangles chasing a single circle. They started with a display of moving triangles and a single moving circle. Then they varied whether the triangles stayed pointed toward the circle or not. When the wolf triangles stayed pointed at the sheep circle, people perceived animacy, thought the triangles were a pack, and were distracted by the wolf pack (you can see an example of the triangles behaving like a wolf pack at this link to the Wolfpack Effect).
People will also quickly group sets of moving dots into single biological entities, into something alive. Gunnar Johansson, back in the early 1970s, created movies of people with points of light at their joints as the people walked, ran, and performed other activities (the points of light were at ankles, knees, hips, wrists, elbows, and shoulders, with one for the head). With the contrast set correctly, all you see is the points of light. When naïve individuals see a single frame from the movie, they can't identify what the dots represent - maybe a Christmas tree. As soon as the motion starts, everyone sees human motion (check out the cool point light walker at the BioMotion Lab Site).
The bias is to see life and attention is quickly captured by biological motion. We share these biases with other animals as well. But this shouldn't be surprising. Natural selection must have placed a value on being able to detect movement - particularly movement by something alive. Biological movement indicates potential prey or predator - would it taste good to me or would I taste good to it.
People not only see certain forms of motion as indicative of life, but they also attribute intention and emotion based on the motion of dots. We see the wolf pack working together if all the triangles stay oriented toward the single circle. If you play with the BioMotion Lab point light walker, you can make those walking dots look happy or sad. In a classic study by Heider and Simmel (1944), interactions of triangles and a circle led people to infer motivations and emotions (you can see the classic motion picture in the Heider and Simmel you-tube video).
All of these studies with moving dots highlight the deep biases in the human cognitive systems. We are prepared to see life. Animate motion grabs our attention. We attribute motivations and emotions quickly and easily. We are cats chasing a laser pointer.