Which visual system has better spatial summation?

The scotopic visual system, which operates primarily under low light conditions, has better spatial summation due to the convergence of multiple rod photoreceptors onto a single bipolar cell. This convergence allows the scotopic system to pool signals from a larger receptive field, improving sensitivity to light and enabling better detection of visual stimuli in dim lighting.

In contrast, the photopic system, which functions well in brighter light conditions and is responsible for color perception and fine detail, relies on the activity of cone photoreceptors. Each cone is typically connected to its own bipolar cell, leading to less convergence and, thus, a smaller receptive field. This results in greater visual acuity but reduced spatial summation compared to the scotopic system.

Understanding this difference highlights why the scotopic system is more effective in situations requiring sensitivity to light patterns over fine detail, especially in low-light environments.