Visual crowding

Crowding makes a target that is easily recognizable in isolation, unrecognizable in clutter. When looking directly at the ‘+’ the letter ‘N’ presented in the right is more easily recognized than the N in the clutter ‘KND’

Visual crowding is the inability to view a target stimulus distinctly when presented in a clutter. Crowding impairs the ability to discriminate object features and contours among flankers, which in turn impairs people's ability to respond appropriately to the target stimulus.[1]

An operational definition of crowding explains what crowding is and how it is different from similar effects such as masking, lateral interaction and surround suppression; effects that make the target more challenging to see as well. There are different criteria that are used to differentiate crowding from these other effects. Firstly, crowding makes it difficult to identify an object but not detecting it among the clutter.[2][3][4] Crowded objects are collectively perceived to have high contrast, but they remain indistinct. The eccentricity of the target and the distance between the target and flankers influence crowding. As the distance between the target and the flankers' increases at a given eccentricity the ability to detect the target also improves as the eccentricity of a target is increased the more it pops out from the flankers and the more easily it is identified.[5]

Crowding is anisotropic, which means it has different values when measured in different directions. Radially positioned flankers make it harder to identify the target than tangentially positioned ones.[6] Crowding is stronger in the upper field of the four quadrants than the lower ones.[7] A recent study tells us that crowding is intense where the distractor and the target are in the same visual field than when they are in separate visual fields despite equal retinal distance.[8] Crowding is also asymmetrical meaning that a single flanker at an eccentric locus higher than the target makes it harder to identify the target than the single flanker at an eccentric locus closer to the fovea.[5] Crowding is not just a spatial phenomenon it happens over time as well, when a target is moving it is found to be more crowded when the flankers are leading than when they follow the target.[9]

  1. ^ Whitney D, Levi DM (April 2011). "Visual crowding: a fundamental limit on conscious perception and object recognition". Trends in Cognitive Sciences. 15 (4): 160–8. doi:10.1016/j.tics.2011.02.005. PMC 3070834. PMID 21420894.
  2. ^ Levi DM, Hariharan S, Klein SA (2002). "Suppressive and facilitatory spatial interactions in peripheral vision: peripheral crowding is neither size invariant nor simple contrast masking". Journal of Vision. 2 (2): 167–77. doi:10.1167/2.2.3. PMID 12678590.
  3. ^ Levi DM, Hariharan S, Klein SA (May 2002). "Suppressive and facilitatory spatial interactions in amblyopic vision". Vision Research. 42 (11): 1379–94. doi:10.1016/S0042-6989(02)00061-5. PMID 12044744.
  4. ^ Pelli DG, Palomares M, Majaj NJ (December 2004). "Crowding is unlike ordinary masking: distinguishing feature integration from detection". Journal of Vision. 4 (12): 1136–69. doi:10.1167/4.12.12. PMID 15669917.
  5. ^ a b Bouma H (April 1970). "Interaction effects in parafoveal letter recognition". Nature. 226 (5241): 177–8. Bibcode:1970Natur.226..177B. doi:10.1038/226177a0. PMID 5437004. S2CID 29459715.
  6. ^ Toet A, Levi DM (July 1992). "The two-dimensional shape of spatial interaction zones in the parafovea". Vision Research. 32 (7): 1349–57. doi:10.1016/0042-6989(92)90227-A. PMID 1455707. S2CID 8123408.
  7. ^ He S, Cavanagh P, Intriligator J (September 1996). "Attentional resolution and the locus of visual awareness". Nature. 383 (6598): 334–7. Bibcode:1996Natur.383..334H. doi:10.1038/383334a0. PMID 8848045. S2CID 4354509.
  8. ^ Liu T, Jiang Y, Sun X, He S (January 2009). "Reduction of the crowding effect in spatially adjacent but cortically remote visual stimuli". Current Biology. 19 (2): 127–32. Bibcode:2009CBio...19..127L. doi:10.1016/j.cub.2008.11.065. PMC 3175242. PMID 19135367.
  9. ^ Bex PJ, Dakin SC, Simmers AJ (December 2003). "The shape and size of crowding for moving targets". Vision Research. 43 (27): 2895–904. doi:10.1016/S0042-6989(03)00460-7. PMID 14568377.