Visual crowding

A limit on peripheral vision: a target that is easily identified in isolation becomes hard to recognize when flanked by nearby similar items, even though it remains visible. Crowding is a failure of object recognition, not of detection — the observer sees that something is there but cannot identify it — and it is indexed by discrimination accuracy in a forced-choice task (e.g. “which way does the target letter point?”).

Why the wiki holds it

Its value here is as a converging, artefact-free test. Breaking-CFS uses reaction-time-like time-to-emergence and depends on interocular competition, both of which have been criticized as confounds. Crowding shares neither: it is an accuracy measure with no rivalry component. So when Salomon et al. (2016) found that visual targets flashed synchronously with the viewer’s own heartbeat were discriminated less accurately under crowding (56% vs 69%), reproducing the cardio-visual suppression they had found with CFS, it ruled out an explanation specific to the breaking-CFS paradigm — the suppression is a general property of cardiac-synchronous vision, not an artefact of one task.