visual crowding

There is much information that gets through to peoples conscious even under the circumstances of crowding these include the appearance of a feature, people can easily perceive the appearance of a feature but cannot identify or discriminate the changes in this feature.{{cite journal | vauthors = Levi DM, Carney T | title = Crowding in peripheral vision: why bigger is better | journal = Current Biology | volume = 19 | issue = 23 | pages = 1988–93 | date = December 2009 | pmid = 19853450 | pmc = 3045113 | doi = 10.1016/j.cub.2009.09.056 | bibcode = 2009CBio...19.1988L }} Secondly, After effects from adaptation survive crowding, adapting to a target in a crowded stimulus can help people form an orientation[8] and track the motion of the target.{{cite journal | vauthors = Aghdaee SM | title = Adaptation to spiral motion in crowding condition | journal = Perception | volume = 34 | issue = 2 | pages = 155–62 | date = 2005 | pmid = 15832566 | doi = 10.1068/p5298 | s2cid = 25291055 }}{{cite journal | vauthors = Whitney D | title = Motion distorts perceived position without awareness of motion | journal = Current Biology | volume = 15 | issue = 9 | pages = R324-6 | date = May 2005 | pmid = 15886084 | pmc = 3890254 | doi = 10.1016/j.cub.2005.04.043 | bibcode = 2005CBio...15.R324W }} Next is combined orientation, even though people are not able to tell the individual orientation of a target stimulus in a crowded setting, they can reliably report an average combined orientation of the stimulus, which means that the orientation signals from the target stimulus are combined than lost.{{cite journal | vauthors = Gheri C, Morgan MJ, Solomon JA | title = The relationship between search efficiency and crowding | journal = Perception | volume = 36 | issue = 12 | pages = 1779–87 | date = 2007 | pmid = 18283928 | pmc = 2590853 | doi = 10.1068/p5595 }}

Some target identity information survives crowding, people can identify more correct targets from a crowded setting when they are asked to report information on both the target and the flanker. Sometimes certain information such as the target information is lost, but the people are able to make better "target “ responses in this condition. Some information on the target is preserved, but most of the times the location information is lost.{{cite journal | vauthors = Popple AV, Levi DM | title = The perception of spatial order at a glance | journal = Vision Research | volume = 45 | issue = 9 | pages = 1085–90 | date = April 2005 | pmid = 15707915 | doi = 10.1016/j.visres.2004.11.008 | doi-access = free }}{{cite journal | vauthors = Strasburger H | title = Unfocused spatial attention underlies the crowding effect in indirect form vision | journal = Journal of Vision | volume = 5 | issue = 11 | pages = 1024–37 | date = December 2005 | pmid = 16441200 | doi = 10.1167/5.11.8 | doi-access = free }}{{cite journal | vauthors = Huckauf A, Knops A, Nuerk HC, Willmes K | title = Semantic processing of crowded stimuli? | journal = Psychological Research | volume = 72 | issue = 6 | pages = 648–56 | date = November 2008 | pmid = 18841386 | doi = 10.1007/s00426-008-0171-5 | s2cid = 10760582 }}

Crowding is broken when the target and stimulus are different than when they are similar. The difference of target group from the flanker group of stimulus in shape, size,{{cite journal | vauthors = Kooi FL, Toet A, Tripathy SP, Levi DM | title = The effect of similarity and duration on spatial interaction in peripheral vision | journal = Spatial Vision | volume = 8 | issue = 2 | pages = 255–79 | date = 1994 | pmid = 7993878 | doi = 10.1163/156856894X00350 }}{{cite journal | vauthors = van den Berg R, Roerdink JB, Cornelissen FW | title = A neurophysiologically plausible population code model for feature integration explains visual crowding | journal = PLOS Computational Biology | volume = 6 | issue = 1 | pages = e1000646 | date = January 2010 | pmid = 20098499 | pmc = 2799670 | doi = 10.1371/journal.pcbi.1000646 | bibcode = 2010PLSCB...6E0646V | doi-access = free }} orientation,{{cite journal | vauthors = Andriessen JJ, Bouma H | title = Eccentric vision: adverse interactions between line segments | journal = Vision Research | volume = 16 | issue = 1 | pages = 71–8 | date = January 1976 | pmid = 1258390 | doi = 10.1016/0042-6989(76)90078-X | s2cid = 23025320 | url = https://research.tue.nl/nl/publications/eccentric-vision--adverse-interactions-between-line-segments(11535f6f-e2ba-4efe-9535-d3463f99dd56).html }}{{cite journal | vauthors = Danilova MV, Bondarko VM | title = Foveal contour interactions and crowding effects at the resolution limit of the visual system | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 25.1–18 | date = November 2007 | pmid = 18217840 | pmc = 2652120 | doi = 10.1167/7.2.25 }} polarity,{{cite journal | vauthors = Chakravarthi R, Cavanagh P | title = Temporal properties of the polarity advantage effect in crowding | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 11.1–13 | date = March 2007 | pmid = 18217826 | doi = 10.1167/7.2.11 | doi-access = free }} spatial frequency,{{cite journal | vauthors = Chung ST, Levi DM, Legge GE | title = Spatial-frequency and contrast properties of crowding | journal = Vision Research | volume = 41 | issue = 14 | pages = 1833–50 | date = June 2001 | pmid = 11369047 | doi = 10.1016/S0042-6989(01)00071-2 | doi-access = free }} depth, color,{{cite journal | vauthors = Põder E, Wagemans J | title = Crowding with conjunctions of simple features | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 23.1–12 | date = November 2007 | pmid = 18217838 | doi = 10.1167/7.2.23 | doi-access = free }} motion and order,{{cite journal | vauthors = Chung ST, Li RW, Levi DM | title = Crowding between first- and second-order letter stimuli in normal foveal and peripheral vision | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 10.1–13 | date = March 2007 | pmid = 18217825 | pmc = 2747649 | doi = 10.1167/7.2.10 }} breaks crowding.  Crowding happens among faces(holistic crowding) having an inverted face flanker when searching for an upright face breaks crowding. Which makes upright faces more effective flankers.{{cite journal | vauthors = Farzin F, Rivera SM, Whitney D | title = Holistic crowding of Mooney faces | journal = Journal of Vision | volume = 9 | issue = 6 | pages = 18.1–15 | date = June 2009 | pmid = 19761309 | pmc = 2857385 | doi = 10.1167/9.6.18 }}{{cite journal | vauthors = Louie EG, Bressler DW, Whitney D | title = Holistic crowding: selective interference between configural representations of faces in crowded scenes | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 24.1–11 | date = November 2007 | pmid = 18217839 | pmc = 3849395 | doi = 10.1167/7.2.24 }} Providing cue about the target location tends to reduce crowding.{{cite journal | vauthors = Yeshurun Y, Rashal E | title = Precueing attention to the target location diminishes crowding and reduces the critical distance | journal = Journal of Vision | volume = 10 | issue = 10 | pages = 16 | date = August 2010 | pmid = 20884481 | doi = 10.1167/10.10.16 | doi-access = free }}{{cite journal | vauthors = Chakravarthi R, Cavanagh P | title = Bilateral field advantage in visual crowding | journal = Vision Research | volume = 49 | issue = 13 | pages = 1638–46 | date = June 2009 | pmid = 19362572 | pmc = 2760476 | doi = 10.1016/j.visres.2009.03.026 }}{{cite journal | vauthors = Freeman J, Pelli DG | title = An escape from crowding | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 22.1–14 | date = October 2007 | pmid = 18217837 | doi = 10.1167/7.2.22 | doi-access = free }} Crowding is broken when the flankers are collectively masked, but this happens only when the flankers are masked with noise or using metacontrast masks but not with substitution masks.{{cite journal | vauthors = Chakravarthi R, Cavanagh P | title = Recovery of a crowded object by masking the flankers: determining the locus of feature integration | journal = Journal of Vision | volume = 9 | issue = 10 | pages = 4.1–9 | date = September 2009 | pmid = 19810785 | pmc = 2766569 | doi = 10.1167/9.10.4 }} When people are adapted to look for a target stimulus in a certain spatial position, it renders the flankers perceptually invisible (adaptation induced blindness), thus releasing the effect of crowding.{{cite journal | vauthors = Wallis TS, Bex PJ | title = Visual crowding is correlated with awareness | journal = Current Biology | volume = 21 | issue = 3 | pages = 254–8 | date = February 2011 | pmid = 21277208 | pmc = 3051843 | doi = 10.1016/j.cub.2011.01.011 | bibcode = 2011CBio...21..254W }}

Neurophysiological studies have not made much progress in narrowing down the locus of the brain at which crowding occurs. Previous researches have demonstrated that crowding is “dichoptical” meaning that the target is perceived by one eye and the distractor by the other.{{cite journal | vauthors = Flom MC, Heath GG, Takahashi E | title = Contour Interaction and Visual Resolution: Contralateral Effects | journal = Science | volume = 142 | issue = 3594 | pages = 979–80 | date = November 1963 | pmid = 14069233 | doi = 10.1126/science.142.3594.979 | bibcode = 1963Sci...142..979F | s2cid = 33685647 }}{{cite journal | vauthors = Tripathy SP, Levi DM | title = Long-range dichoptic interactions in the human visual cortex in the region corresponding to the blind spot | journal = Vision Research | volume = 34 | issue = 9 | pages = 1127–38 | date = May 1994 | pmid = 8184557 | doi = 10.1016/0042-6989(94)90295-X | s2cid = 15338292 }} Which should mean that the effect of crowding occurs in the cortex. Different researchers have claimed different sites to be the processing center for crowding e.g. (V1,{{cite journal | vauthors = Pelli DG | title = Crowding: a cortical constraint on object recognition | journal = Current Opinion in Neurobiology | volume = 18 | issue = 4 | pages = 445–51 | date = August 2008 | pmid = 18835355 | pmc = 3624758 | doi = 10.1016/j.conb.2008.09.008 }} V2, V3,{{cite journal | vauthors = Tyler CW, Likova LT | title = Crowding: a neuroanalytic approach | journal = Journal of Vision | volume = 7 | issue = 2 | pages = 16.1–9 | date = July 2007 | pmid = 18217831 | doi = 10.1167/7.2.16 | doi-access = free }}{{cite journal | vauthors = Bi T, Cai P, Zhou T, Fang F | title = The effect of crowding on orientation-selective adaptation in human early visual cortex | journal = Journal of Vision | volume = 9 | issue = 11 | pages = 13.1–10 | date = October 2009 | pmid = 20053076 | doi = 10.1167/9.11.13 | doi-access = free }} V4{{cite journal | vauthors = Motter BC | title = Modulation of transient and sustained response components of V4 neurons by temporal crowding in flashed stimulus sequences | journal = The Journal of Neuroscience | volume = 26 | issue = 38 | pages = 9683–94 | date = September 2006 | pmid = 16988039 | pmc = 6674438 | doi = 10.1523/JNEUROSCI.5495-05.2006 }}{{cite journal | vauthors = Merigan WH | title = Cortical area V4 is critical for certain texture discriminations, but this effect is not dependent on attention | journal = Visual Neuroscience | volume = 17 | issue = 6 | pages = 949–58 | date = November 2000 | pmid = 11193111 | doi = 10.1017/S095252380017614X | s2cid = 13095796 }} some researchers claim crowding happens at a later stage of visual processing). So, the locus of the brain at which crowding occurs is still not clearly defined.

From the many models that try and explain the process of crowding, there is still a lack of an actual model that helps predict the entirety of how crowding works. All models have three major division that remains as its essence: masking, pooling and substitution. The pooling can be of the low-level features or the pooling of attention. One of the model that nicely predicts is the model by Wilkinson where he boils down the process of crowding to the interaction between complex cells and simple cells, where the simple cells suppress weak complex cell responses and the complex cells respond actively resulted from spatial pooling and then they suppress simple cell activity in their receptive cell area[41].

Another model that best predicts crowding process proposes a quantitative model for a spatial integration of orientation signals, As per the principles of population coding, this model satisfactorily predicts properties like critical spacing, compulsory averaging and the inner and outer asymmetry.

Different studies implicitly assume that crowding is a unitary effect due to a single stage of processing.{{cite journal | vauthors = Levi DM | title = Crowding--an essential bottleneck for object recognition: a mini-review | journal = Vision Research | volume = 48 | issue = 5 | pages = 635–54 | date = February 2008 | pmid = 18226828 | pmc = 2268888 | doi = 10.1016/j.visres.2007.12.009 }} The other notion states that crowding happens independently at several stages of visual processing. This notion supports the view that crowding is influenced by the similarity and configuration of flankers and the target. By this notion, the effect is selectively observed between whole objects, object parts,{{cite journal | vauthors = Martelli M, Majaj NJ, Pelli DG | title = Are faces processed like words? A diagnostic test for recognition by parts | journal = Journal of Vision | volume = 5 | issue = 1 | pages = 58–70 | date = February 2005 | pmid = 15831067 | doi = 10.1167/5.1.6 | doi-access = free }} and features. This view is also consistent with Bouma's law. This view has gained much support. Crowding in a natural setting may also occur in layers depending on the location, content and attention dependence.

Herman Bouma, a Dutch vision researcher and gerontologist stated, “For complete visual isolation of a letter presented at an eccentricity of φ deg, … no other letters should be present within (roughly) 0.5 φ distance." At a later stage, he reduced the proportionality constant from 0.5 to 0.4. This gave rise to the notion of “critical spacing” which is proportional to the eccentricity. Critical spacing is the sufficient distance needed for the identification of an object among its flankers in the retinotopically organized cortex. Bouma explains how the effect of crowding is dependent on the eccentricity of a subject and the distance between the flankers and the object. Many studies support the claim that critical space needed for crowding depends on the eccentricity of the subject.{{cite journal | vauthors = Tripathy SP, Cavanagh P | title = The extent of crowding in peripheral vision does not scale with target size | journal = Vision Research | volume = 42 | issue = 20 | pages = 2357–69 | date = September 2002 | pmid = 12350424 | doi = 10.1016/S0042-6989(02)00197-9 | doi-access = free }} The proportionality constant named b, after Bouma, is dependent on how similar the flankers are to the target, the number of possible targets, and the arbitrary threshold criterion.{{cite journal | vauthors = Pelli DG, Tillman KA | title = The uncrowded window of object recognition | journal = Nature Neuroscience | volume = 11 | issue = 10 | pages = 1129–35 | date = October 2008 | pmid = 18828191 | pmc = 2772078 | doi = 10.1038/nn.2187 }} The value of Boumas proportionality constant ‘b’ is different among studies, but most of the times it is reported to be ≈0.4 - 0.5. This rule is sometimes raised to the status of a 'law' but this remains controversial.

{{Reflist|32em}}

Category:Vision