Crowding

Yet, while it is indeed particularly prominent there, it is present in the whole of the visual field, with only its spatial extent varying (governed by Bouma's law; see below).

Newer research suggests that the factor in Bouma's rule (originally ½) can vary quite a bit, and might often be a little smaller (e.g., 0.4).

[21][10] Crowding, as we know today, is – except in a few special circumstances – the essential bottleneck[4] for human pattern recognition and can be demonstrated in the easiest of ways.

[22] In the 19th century, the ophthalmologists Hermann Aubert and Richard Förster in Breslau/Poland described the percept of two neighboring points in indirect vision as “quite strangely undefined ["ganz eigenthümlich unbestimmt"] as something black, the form of which cannot be further specified”.

[5] Probably around that time, crowding has become an issue in optometry and ophthalmology when testing amblyopic subjects with eye charts, as is apparent from a remark of the Danish ophthalmologist Holger Ehlers in 1936.

[13] James A. Stuart und Hermann M. Burian in Iowa were, in 1962, the first to study crowding systematically, for amblyopic subjects.

[14] In foveal vision, the related phenomenon of contour interaction was described (Merton Flom, Frank Weymouth & Daniel Kahneman, 1963).