The 10 minute arc stimulus was used to investigate which phenomenon?

• A. Temporal summation
• B. Color vision
• C. Lateral inhibition
• D. Spatial summation

Answer: (D)

Spatial summation describes how the visual system pools light across neighboring photoreceptors to detect a stimulus. A stimulus spanning ten minutes of arc is small enough to target the retina’s receptive field but large enough to recruit signals from multiple photoreceptors within that field, so detection thresholds reflect how signals are combined across space. This is precisely what spatial summation measures: how increasing the stimulus area changes the sensitivity of vision due to spatial pooling. Lateral inhibition focuses on edge contrast from center–surround antagonism, not the simple detection of a uniform patch across space. Color vision involves chromatic processing rather than the spatial pooling of light in the retina. Temporal summation would involve integrating light over time, not over space.