Which photoreceptors have directional sensitivity?

• A. Rods
• B. Both
• C. Cones
• D. Neither

Answer: (C)

Directionality in vision comes from how finely the retina samples the image. Cones provide high-acuity sampling because they have small, tightly packed receptive fields, especially in the fovea. This means a light source or edge will activate a distinct pattern of neighboring cones, letting the brain infer where the light is coming from and which direction a stimulus is moving. The precise spatial information from many cones allows better discrimination of direction than if the signal were averaged over a large area.

Rods, by contrast, are highly sensitive in low light but tend to pool signals over large receptive fields as they converge to downstream neurons. That pooling smooths out spatial details, so they carry less information about the exact location or direction of a light source. In bright light, this reduced spatial specificity further limits direction perception.

So, cones support directional sensitivity because their high spatial resolution provides the detailed positional information the brain uses to judge where light is coming from.