When the lights go down, the world may appear to slow, new research suggests. Movement perceived by rods, the cells in the retina that register dim lights, looks slower than the same motion detected by the color-sensitive cones.
Most people see the world through four types of visual-receptor cells.
Rods sense brightness alone, while the three types of cones register red, green, and blue wavelengths of light. For example, Gegenfurtner knew of a color-blind man lacking all three types of cone cells who complained of trouble catching a Frisbee. About 2 percent of white men can't distinguish green and red because they are missing the cone cells tuned to green light. The rod cells may see the world differently because of the way the retina is wired, says Banks. In very low light, only the rod cells are sensitive enough to see the dimmest objects.