As cones move away from the fovea, what happens to the degree of spatial summation?

• A. Decreases
• B. Stays the same
• C. Increases
• D. Disappears

Answer: (C)

Spatial summation depends on how much neighboring photoreceptors’ signals are pooled by downstream neurons. In the fovea, cone receptors have very small receptive fields and there is minimal pooling, which preserves fine spatial detail. As you move away from the fovea, more cones share a single downstream neuron, and receptive fields become larger. This increased convergence means light from a larger area is summed together, raising the degree of spatial summation. So, cones farther from the fovea integrate information over a bigger region, making the tuning more about detecting overall light levels than about resolving fine detail.