Twilight conditions are mediated by which photoreceptors?

• A. Rods
• B. Cones
• C. Rods and cones
• D. Ganglion cells

Answer: (C)

Twilight vision relies on both rods and cones. In dim, twilight conditions the rods are highly sensitive and can respond to low light, driving vision, but they don’t convey color and have less spatial detail. At the same time, some cone activity persists, supplying color information and better visual detail than rods alone. The combination of signals from both photoreceptor types—the rod and cone pathways—produces the usable vision you have at dusk or dawn, known as mesopic vision. Ganglion cells are the output neurons that receive input from photoreceptors, so they aren’t the photoreceptors themselves.