How the visual system constructs moving objects

August 15, 2011

Although our eyes record the word as pixels, the visual system is fantastic at giving us a world that looks like objects, not pixels, psychologists atĀ Northwestern University haveĀ found.

It does this by grouping areas of the world with similar characteristics, such as color, shape, or motion, the researchers said.

The process is so seamless that we feel we’re taking it all in simultaneously. The psychologists said this is actually an illusion. For some types of grouping, the visual system is limited by its ability to perceive only one group at a time.

How does this grouping work? Say you’re looking at a crowded street, with cars going every which way. Your view of each individual car is partially blocked, so that you actually see multiple “pieces” of each. Yet because those pieces move with the same direction of motion, grouping by “common fate” helps you perceive whole cars.

To demonstrate this point, the researchers performed two experiments, simplifying the “car pieces” into pairs of moving dots. In the first experiment, participants had to find the pairs that were vertically arranged among pairs that were horizontally arranged. In the second, instead of finding a group with a specific shape, they were asked to find a group among non-groups — like whole cars among scattered pieces.

In both tasks, people were surprisingly slow, the researchers said. As participants were asked to make decisions involving more groups, they took more and more time. They were limited by their one-at-a-time visual systems that needed to flip through the groups, at a rate of about 10 per second.

The research, says Franconeri, offers practical information for people creating effective complex graphic systems such as charts and graphs, and even more complex visualizations, such as genomic sequences.

Ref.: Brian R. Levinthal and Steven L. Franconeri, Common-Fate Grouping as Feature Selection, Psychological Science, published online 9 August 2011; [DOI: 10.1177/0956797611418346]