Conservation of cortical crowding distance across individuals in human V4.

Crowding is the failure to recognize an object due to insufficient spacing, which slows daily tasks such as reading and search. Across 49 observers, we found large variations in psychophysical crowding distance and retinotopic map size. These measures covary, conserving a 1.4-mm cortical crowding distance (threshold object spacing on the cortical surface) in the human V4 map, but not V1-V3. This links the spacing limit of visual recognition to overall V4 size.