Princeton's WordNet(0.00 / 0 votes)Rate this definition: 1  shimmer, play(verb) a weak and tremulous light. 2  shimmer(verb) shine with a weak or fitful light. 3  shimmer(verb) give off a shimmering reflection, as of silk.
Cats, like humans, have both rods and cones in the retina. Rods are the receptors that the eye uses for night time viewing and sudden movement. Cones are used during the daytime, and process color information. Cats have more rods than cones, as compared with humans, making cat night vision superior to humans.
Rods and cones are photoreceptors that are located in the retina of the eye. Rods are responsible for vision at low light levels while cones are responsible for vision at higher light levels. Therefore, rods are very sensitive to light. Rods work well at night when light is low. Cones, however, are responsible for color vision and high visual spatial acuity. Therefore, rods cannot distinguish colors. With these differences, the correct answer is: A. Rods are very sensitive to light but do not distinguish colors.