How does color tell us about motion?

The human brain is incredibly specialized. There are individual neurons for recognizing faces, edges of objects, and specific sounds. One fruitful area of research recently has been to determine precisely how specialized the brain really is. Here's one example. The image below links to an animated movie. Click on it and see how quickly you can determine which direction the rectangles are moving:

If you're like most adults, you're able to determine the correct direction very quickly.

Now, take a look at this animation and try it again:

This one should have taken somewhat longer, even though it was moving the same direction as the first one. What's the difference? In the second animation, only the changing colors cue us to the direction of motion; in the first, we get an additional cue because the yellow rectangles only move a half-step between each frame. This and other research has led psychologists to believe that color and motion are processed separately in adults. The reason it takes longer to process the second animation is because the color information is processed first, then other parts of the brain must interpret that color change as motion.

Karen Dobkins and Christina Anderson wondered whether we're born with brains that process color separately from motion, or if this is a later development. To answer their question, they showed adults and babies animations similar to the ones above, but with a twist. When they showed the sharply contrasting black and yellow animation, they presented this animation with several different levels of contrast, gradually decreasing the contrast until it was just as difficult to determine the direction of the yellow rectangles as it was for the colored ones. Here's a summary of their results:

The vertical axis is the percentage of contrast compared to the original, 100 percent yellow-and-black animation in order for participants to have the same difficulty seeing motion as they did in the color animation (a rate of 75 percent correct). For adults, it was just a tiny fraction of the original level of contrast, but for the youngest babies, equivalence was reached at 10 percent of the original contrast level (I don't have Dobkins and Anderson's graphics, but here's a guess at what that might have looked like).

Dobkins and Anderson argue that this means that babies have not yet separated the processes of color detection and motion detection. If the colored animation gives adults so much difficulty that an extremely low-contrast black and yellow animation—more than 100 times lower than for babies—is its equivalent, then it must be because babies are processing the information differently from adult. Babies are better than adults at perceiving motion from color differences.

(A side note: How do you tell if a baby perceives motion? Watch their eyes. An independent observer, unaware of the particular animation the baby was watching, observed the baby's eyes to see which direction they were moving. When the eyes moved in the same direction as the animated motion, the researchers determined that the baby perceived the motion. The same method was used with the adults in this experiment.)

Dobkins, K.R., & Anderson, C.M. (2002). Color-based motion processing is stronger in infants than in adults. Psychological Science, 13(1), 76-80.