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A demonstration of the crowding effect. Fixate on the "x" and attempt to identify the central (or single) letter appearing to the right. The presence of flankers should make the task more difficult.

Crowding is a perceptual phenomenon where the recognition of objects presented away from the fovea is impaired by the presence of other neighbouring objects (sometimes called "flankers").[1] It has been suggested that crowding occurs due to mandatory integration of the crowded objects by a texture-processing neural mechanism.[2] It is considered a kind of grouping since it is "a form of integration over space as target features are spuriously combined with flanker features."[3]

Crowding deficits have been specifically found in neuropsychiatric disorders such as schizophrenia and autism and may have clinical implications in these disorders.[4] It also suggested that head injuries can cause a crowding effect.[5]


  1. ^ Levi D (February 2008). "Crowding - an essential bottleneck for object recognition: a mini-review". Vision Research. 48 (5): 635–654. doi:10.1016/j.visres.2007.12.009. PMC 2268888. PMID 18226828.
  2. ^ Parkes L; Lund J; Angelucci A; Solomon JA; Morgan M (2001). "Compulsory averaging of crowded orientation signals in human vision". Nature Neuroscience. 4 (7): 739–744. doi:10.1038/89532.
  3. ^ Wixted, John (2018). Stevens' Handbook of Experimental Psychology and Cognitive Neuroscience, Sensation, Perception, and Attention, Fourth Edition Volume 2. Hoboken, NJ: John Wiley & Sons. p. 833. ISBN 9781119170044.
  4. ^ Kraehenmann, Rainer; Vollenweider FX; Seifritz E; Kometer M (2012). "Crowding deficits in the visual periphery of schizophrenia patients". PLOS ONE. 7 (9): e45884. doi:10.1371/journal.pone.0045884. PMC 3458825. PMID 23049884.
  5. ^ Millichap, Gordon (2009). Attention Deficit Hyperactivity Disorder Handbook: A Physician's Guide to ADHD, Second Edition. New York: Springer Science+Business Media. p. 17. ISBN 9781441913968.