Strong Crowding Research Articles

Reduction of the Crowding Effect in Spatially Adjacent but Cortically Remote Visual Stimuli

When embedded in adjacent distractors, a target becomes more difficult to perceive. The neural mechanism for this ubiquitous visual crowding effect remains unresolved. Stimuli presented on opposite sides of the vertical meridian initially project to different hemispheres, whereas stimuli with the same spatial distance but presented to one side of the vertical meridian project to the same hemisphere. Dissociation between visual spatial distance and cortical distance can also be found in V2 and V3 (quadrant representations of the visual hemifield) along the horizontal meridian. In the current study, we observed a strong crowding effect from spatially adjacent distractors with either Gabor or letter targets presented near the vertical or horizontal meridian. Interestingly, for a target presented near the vertical meridian, a distractor from the same side of the meridian (cortically near) had a significantly stronger crowding effect compared with an equidistant distractor presented on the opposite side (cortically remote). No such meridian modulation was observed across the horizontal meridian. These results constrain the cortical locus of the crowding effect to a stage in which left and right visual spaces are represented discontinuously but the upper and lower visual fields are represented continuously, likely beyond the early retinotopic areas.

Crowding Out Informal Care? Evidence from a Social Experiment in Germany

This paper evaluates the effects of a professionally assisted consumer-directed program (Personal Budgets) compared to the standard home care programs of the German long-term care insurance. The evaluation makes use of a long-run social experiment at seven different sites with a random assignment into a treatment group receiving personal budgets and a control group in standard home care programs, i.e. an in-kind benefit (agency care) and cash payments. Compared to agency care personal budgets yield better care outcomes with regard to the overall support of formal and informal caregivers. In contrast, personal budgets do not improve care outcomes compared to the much less generous cash payments due to a strong crowding out of informal by formal care.

Image segregation in strabismic amblyopia

Humans with naturally occurring amblyopia show deficits thought to involve mechanisms downstream of V1. These include excessive crowding, abnormal global image processing, spatial sampling and symmetry detection and undercounting. Several recent studies suggest that humans with naturally occurring amblyopia show deficits in global image segregation. The current experiments were designed to study figure–ground segregation in amblyopic observers with documented deficits in crowding, symmetry detection, spatial sampling and counting, using similar stimuli. Observers had to discriminate the orientation of a figure (an “E”-like pattern made up of 17 horizontal Gabor patches), embedded in a 7 × 7 array of Gabor patches. When the 32 “background” patches are vertical, the “E” pops-out, due to segregation by orientation and performance is perfect; however, if the background patches are all, or mostly horizontal, the “E” is camouflaged, and performance is random. Using a method of constant stimuli, we varied the number of “background” patches that were vertical and measured the probability of correct discrimination of the global orientation of the E (up/down/left/right). Surprisingly, amblyopes who showed strong crowding and deficits in symmetry detection and counting, perform normally or very nearly so in this segregation task. I therefore conclude that these deficits are not a consequence of abnormal segregation of figure from background.

Crowding is directed to the fovea and preserves only feature contrast

The abundant literature on crowding offers fairly simple explanations for the phenomenon, such as position uncertainty or feature pooling, but convincing evidence to support these explanations is lacking. In part, this is because the stimuli used for crowding studies are usually letters or other complex shapes, which makes it hard to determine exactly what kind of information is lost. In our experiment, we asked observers to identify simultaneously the slants (left or right) of three horizontally aligned Gabor targets. The targets were presented at 6 degrees in the periphery, and their size and separation were chosen to incur strong crowding. The loss of information about the position or orientation of individual members of the Gabor triads does not explain our results. Instead, crowding appears to be a particular form of collective information loss. Firstly, the outmost target was crowded much less than the other targets, which rules out explanations based on simple pooling and shows that crowding has a pronounced foveal directionality. Secondly, the specific pattern of confusion shown by all the observers indicates that the only reliable information available to them was orientation contrast, that is, the number (and, to a lesser degree, the location) of sites where slant changed. Thus, crowding appears to spare only the most salient peripheral information, which supports the hypothesis that crowding is caused by limitations of attentional resolution.

A role for macromolecular crowding effects in the assembly and function of compartments in the nucleus

The mechanisms which cause macromolecules to form discrete compartments within the nucleus are not understood. Here, two ubiquitous compartments, nucleoli, and PML bodies, are shown to disassemble when K562 cell nuclei expand in medium of low monovalent cation concentration; their major proteins dispersed as seen by immunofluorescence and immunoelectron microscopy, and nucleolar transcript elongation fell by ∼85%. These compartments reassembled and nucleolar transcription recovered in the same medium after adding inert, penetrating macromolecules (8 kDa polyethylene glycol (PEG), or 10.5 kDa dextran) to 12% w/v, showing that disassembly was not caused by the low cation concentration. These responses satisfy the criteria for crowding or volume exclusion effects which occur in concentrated mixtures of macromolecules; upon expansion the macromolecular concentration within the nucleus falls, and can be restored by PEG or dextran. These observations, together with evidence of a high concentration of macromolecules in the nucleus (in the range of 100 mg/ml) which must cause strong crowding forces, suggest strongly that these forces play an essential role in driving the formation, and maintaining the function of nuclear compartments. This view is consistent with their dynamic and mobile nature and can provide interpretations of several unexplained observations in nuclear biology.

Do Incentive Contracts Crowd Out Voluntary Cooperation?

In this paper we provide experimental evidence indicating that incentive contracts may cause a strong crowding out of reciprocity-driven voluntary cooperation. This crowding out effect constitutes costs of incentive provision that have been largely neglected by economists. In our experiments the crowding out effect is so strong that the incentive contracts are less efficient than contracts without any incentives. Principals, nonetheless, prefer the incentive contracts because they allow them to appropriate a much larger share of the (smaller) total surplus and are, hence, more profitable for them.

Brief communication: possible third molar impactions in the hominid fossil record.

Impacted third molars affect 15%-20% of modern Americans and Western Europeans. In contrast, third molar impactions have not been reported in the early hominid fossil record. It is uncertain whether the lack of reports reflects an absence of impactions or a failure to recognize them. This communication is intended to raise awareness of the possibility of impactions by describing the appearance of impacted teeth and by noting two possible instances of impaction in early hominids. Specifically, the mandibular third molars of the Sterkfontein specimen, STS52b (Australopithecus africanus), and the left maxillary third molar of the Lake Turkana specimen, KNM-WT 17400 (Australopithecus boisei), are positioned in a manner which suggests that they would not have erupted normally. Both specimens also exhibit strong crowding of the anterior dentition, providing further support for the view that these individuals lacked sufficient space for normal eruption of the third molars. Other published reports of dental crowding in the hominid fossil record are noted, and it is suggested that more attention be paid to dental impaction and dental crowding in hominid evolution.