For vision, at least. Spacing, Not Size, Matters in Visual Recognition, NYU Researchers Find

New York University neuroscientists have concluded that it’s the spacing between letters, not their size, that matters. In general, objects, such as letters, can be recognized only if they are separated by enough space, the “critical spacing.” Objects closer than that spacing are “crowded” and cannot be identified. A broad review of this crowding phenomenon, appearing in the latest issue of the journal Nature Neuroscience, shows that this critical spacing is the same for all objects, including letters, animals, and furniture.

No mention if the Rayleigh criterion is responsible for this.