Strong Crowding Research Articles

Assessing Crowding Perceptions and Satisfaction Among Diverse Visitors at El Yunque National Forest, Puerto Rico

Increased visitation is a concern for many parks and forests due to associated impacts on the environment and the recreation experience. Crowding continues to be one of public land managers’ most challenging problems. El Yunque National Forest (EYNF) is the only tropical national forest in the National Forest System and, at the time of this study, received over one million visits per year. This study aimed to assess crowding perceptions and satisfaction with the recreation experience and the facilities and services available at EYNF among local and non-local visitors. This study has not identified a strong crowding sensitivity among visitors. However, local visitors expressed a higher level of tolerance for recreation encounters as compared with non-locals. Satisfaction with various facilities and services captured an indirect impact of crowding on the experience. This study expands the current understanding of crowding and satisfaction among visitors of diverse cultural backgrounds.

Conformal Mapping of a Z-Shaped Domain

For the problem of conformal mapping of a half-plane onto a Z-shaped domain with arbitrary geometry, an efficient method is developed for finding parameters of the Schwarz–Christoffel integral, i.e., the preimages of the vertices (prevertices) and the pre-integral multiplier. Special attention is given to the situation of crowding prevertices, in which case conventional integration methods face significant difficulties. For this purpose, the concept of a cluster is introduced, its center is determined, and all integrand binomials with prevertices from this cluster are expanded into a fast-convergent series by applying a unified scheme. Next, the arising integrals are reduced to single or double series in terms of Gauss hypergeometric functions F(a, b, c, q). The fast convergence of the resulting expansions is ensured by applying formulas for analytic continuation of F(a, b, c, q) to a neighborhood of the point q = 1 and using numerically stable recurrence relations. The constructed expansions are also fairly efficient for choosing initial approximations for prevertices in Newton’s iteration method. By using the leading terms of these expansions, the approximations for the prevertices are expressed in explicit form in terms of elementary functions, and the subsequent iterations ensure the fast convergence of the algorithm. After finding the parameters in the integral, the desired mapping is constructed as a combination of power series expansions at prevertices, regular expansions at the preimage of the center of symmetry, a Laurent series in a semi-annulus, and special series near the preimages of the vertical segments. Numerical results demonstrate the high efficiency of the developed method, especially in the case of strong crowding of prevertices.

Context-dependent attentional spotlight in pulvinar-V1 interaction

Spatial attention is often described as a mental spotlight that enhances information processing at the attended location. Using fMRI, we investigated background connectivity between the pulvinar and V1 in relation to focused versus diffused attention allocation, in weak and strong crowding contexts. Our findings revealed that focused attention led to enhanced correlations between the pulvinar and V1. Notably, this modulation was initiated by the pulvinar, and the strength of the modulation was dependent on the saliency of the target. These findings suggest that the pulvinar initiates information reweighting to V1, which underlies attentional selection in cluttered scenes.

Unlocking crowding by ensemble statistics

In crowding,1,2,3,4,5,6,7 objects that can be easily recognized in isolation appear jumbled when surrounded by other elements.8 Traditionally, crowding is explained by local pooling mechanisms,3,6,9,10,11,12,13,14,15 but many findings have shown that the global configuration of the entire stimulus display, rather than local aspects, determines crowding.8,16,17,18,19,20,21,22,23,24,25,26,27,28 However, understanding global configurations is challenging because even slight changes can lead from crowding to uncrowding and vice versa.23,25,28,29 Unfortunately, the number of configurations to explore is virtually infinite. Here, we show that one does not need to know the specific configuration of flankers to determine crowding strength but only their ensemble statistics, which allow for the rapid computation of groups within the stimulus display.30,31,32,33,34,35,36,37 To investigate the role of ensemble statistics in (un)crowding, we used a classic vernier offset discrimination task in which the vernier was flanked by multiple squares. We manipulated the orientation statistics of the squares based on the following rationale: a central square with an orientation different from the mean orientation of the other squares stands out from the rest and groups with the vernier, causing strong crowding. If, on the other hand, all squares group together, the vernier is the only element that stands out, and crowding is weak. These effects should depend exclusively on the perceived ensemble statistics, i.e., on the mean orientation of the squares and not on their individual orientations. In two experiments, we confirmed these predictions.

Functional Field of View Determined by Crowding, Aging, or Glaucoma Under Divided Attention.

PurposeParafoveal or peripheral vision is important for various everyday activities. This is particularly relevant to those who suffer from visual field defects. Here we quantified the effect of visual crowding, normal aging, and glaucoma on the spatial extent of the functional field of view (FFV) under divided attention.MethodsUnlike visual acuity measured by single-letter recognition or visual perimetry measured by light spot detection, we measured the FFV using a target letter presented either alone or in letter triplets appearing across the visual field. A subject's task was to report whether the target letter was the same as the letter displayed concurrently at the central fixation region (i.e., divided attention task). Over the trials, a plot of the proportion correct for letter recognition versus target location was constructed, resulting in a visual field map.ResultsThe results obtained from three subject groups—normal young adults, normal older adults, and patients with glaucoma—showed that on average the central 20° visual field was relatively robust to uncrowded target recognition under divided attention. However, the FFV shrunk down to the central 10° visual field when the target appeared in clutter, suggesting a strong crowding effect on FFV. An additional shrinkage of the FFV occurred in the presence of aging and glaucoma.ConclusionsUsing a quantitative method, we demonstrate that crowding, aging, and glaucoma independently decrease the spatial extent of FFV under divided attention and that crowding seems to be the major contributor limiting FFV.Translational RelevanceOur FFV test may complement standard clinical measurements by providing functionally relevant visual field information.

Non-Gaussian, transiently anomalous, and ergodic self-diffusion of flexible dumbbells in crowded two-dimensional environments: Coupled translational and rotational motions.

We employ Langevin-dynamics simulations to unveil non-Brownian and non-Gaussian center-of-mass self-diffusion of massive flexible dumbbell-shaped particles in crowded two-dimensional solutions. We study the intradumbbell dynamics of the relative motion of the two constituent elastically coupled disks. Our main focus is on effects of the crowding fraction ϕ and of the particle structure on the diffusion characteristics. We evaluate the time-averaged mean-squared displacement (TAMSD), the displacement probability-density function (PDF), and the displacement autocorrelation function (ACF) of the dimers. For the TAMSD at highly crowded conditions of dumbbells, e.g., we observe a transition from the short-time ballistic behavior, via an intermediate subdiffusive regime, to long-time Brownian-like spreading dynamics. The crowded system of dimers exhibits two distinct diffusion regimes distinguished by the scaling exponent of the TAMSD, the dependence of the diffusivity on ϕ, and the features of the displacement-ACF. We attribute these regimes to a crowding-induced transition from viscous to viscoelastic diffusion upon growing ϕ. We also analyze the relative motion in the dimers, finding that larger ϕ suppress their vibrations and yield strongly non-Gaussian PDFs of rotational displacements. For the diffusion coefficients D(ϕ) of translational and rotational motion of the dumbbells an exponential decay with ϕ for weak and a power-law variation D(ϕ)∝(ϕ-ϕ^{★})^{2.4} for strong crowding is found. A comparison of simulation results with theoretical predictions for D(ϕ) is discussed and some relevant experimental systems are overviewed.

Object-based biased competition during covert spatial orienting.

Biased-competition models assert that spatial attention facilitates visual perception by biasing competitive interactions in favor of relevant input. In line with this view, past work has shown that the benefits of covert spatial attention are greatest when targets must compete with interfering stimuli. Here we propose a boundary condition for the resolution of interference via exogenous attention: Attention resolves visual interference between targets and distractors, but only when they can be individuated into distinct representations. Thus, we propose that biased competition may be object-based. We replicated previous observations of larger attention effects when targets were flanked by irrelevant distractors (interference-present displays) than when targets were presented alone (interference-absent displays). Critically, we then showed that this amplification of cueing effects in the presence of interference is eliminated when strong crowding hampers individuation of the targets and distractors. Likewise, when targets were embedded within a noise mask that did not evoke the percept of an individuated distractor, the attention effects were equivalent across noise and lone-target displays. Thus, we conclude that exogenous spatial attention resolves interference in an object-based fashion that depends on the perception of individuated targets and distractors.

Contextual-Dependent Attention Effect on Crowded Orientation Signals in Human Visual Cortex.

A target becomes hard to identify with nearby visual stimuli. This phenomenon, known as crowding, places a fundamental limit on conscious perception and object recognition. To understand the neural representation of crowded stimuli, we used fMRI and a forward encoding model to reconstruct the target-specific feature from multivoxel activation patterns evoked by orientation patches. Orientation-selective response profiles were constructed in V1-V4 for a target embedded in different contexts. Subjects of both sexes either directed their attention over all the orientation patches or selectively to the target. In the context with a weak crowding effect, attending to the target enhanced the orientation selectivity of the response profile; such effect increased along the visual pathway. In the context with a strong crowding effect, attending to the target enhanced the orientation selectivity of the response profile in the earlier visual area, but not in V4. The increase and decrease of orientation selectivity along the visual hierarchy demonstrate a contextual-dependent attention effect on crowded orientation signals: in the context with a weak crowding effect, selective attention gradually resolves the target from nearby distractors along the hierarchy; in the context with a strong crowding effect, while selective attention maintains the target feature in the earlier visual area, its effect decreases in the downstream area. Our findings reveal how the human visual system represents the target-specific feature at multiple stages under the limit of attention selection in a cluttered scene.SIGNIFICANCE STATEMENT Using fMRI and a forward encoding model, we reconstructed orientation-selective response profiles for a target embedded in crowded contexts. In the context with a weak crowding effect, attention gradually resolves the target from nearby distractors along the visual hierarchy. In the context with a strong crowding effect, while the feature of the target is preserved in the early visual cortex, it degrades in the later visual processing stage. The increase and decrease of orientation selectivity along the visual hierarchy reveal how the human visual system strikes to present the target-specific feature under the limit of attention selection in a cluttered scene.

Awareness in the crowd: Beta power and alpha phase of prestimulus oscillations predict object discrimination in visual crowding.

Visual crowding is among the factors that most hamper conscious object perception. However, we currently ignore the neural states that predispose to an accurate perception within different crowding regimes. Here, we performed single-trial analyses of the electroencephalographical (EEG) oscillations, evaluating the prestimulus power and phase differences between correct and incorrect discrimination during a letter-crowding task, where irrelevant letters were placed nearby (strong crowding) or far (mid crowding) relative to the target. Results show that prestimulus alpha (8-12Hz) power was related to target discrimination in the mid, but not in the strong, crowding condition. Importantly, accurate discrimination in the strong crowding condition was predicted by the phase of alpha and by the power of beta (13-20Hz) oscillations. These evidence suggest that both periodic visual sampling mechanisms, reflected in the alpha phase, and network predisposition to extract local information, reflected in the beta power, predispose to object discrimination in a crowded scene.

Typical magnitude and spatial extent of crowding in autism.

Enhanced spatial processing of local visual details has been reported in individuals with autism spectrum conditions (ASC), and crowding is postulated to be a mechanism that may produce this ability. However, evidence for atypical crowding in ASC is mixed, with some studies reporting a complete lack of crowding in autism and others reporting a typical magnitude of crowding between individuals with and without ASC. Here, we aim to disambiguate these conflicting results by testing both the magnitude and the spatial extent of crowding in individuals with ASC (N = 25) and age- and IQ-matched controls (N = 23) during an orientation discrimination task. We find a strong crowding effect in individuals with and without ASC, which falls off as the distance between target and flanker is increased. Both the magnitude and the spatial range of this effect were comparable between individuals with and without ASC. We also find typical (uncrowded) orientation discrimination thresholds in individuals with ASC. These findings suggest that the spatial extent of crowding is unremarkable in ASC, and is therefore unlikely to account for the visual symptoms reported in individuals with the diagnosis.

ACO-AFSA Algorithm in Function Optimization and Its Application

ACO and AFSA as two kinds of new intelligent bionic algorithm, has better robustness, and the design method is simple and easy to understand. At present, in many engineering fields, they have been a pivotal position, but there are some defects in solving function optimization problems. Because of the lack of pheromone in the initial stage of ACO, the speed of the solution is relatively slow, and AFSA has the advantages of strong global convergence ability and fast speed. In this paper, based on the advantages and disadvantages of ACO and AFSA, two kinds of algorithms are integrated, and the advantage is enhanced, a better optimization algorithm is put forward: ACO-AFSA. The initial solution and improved state transition probabilities are obtained by AFSA, and the basic ACO is improved, the congestion degree of AFSA is introduced in the algorithm, makes most of ants’ initial optimization will not be randomly selected at a strong crowding restrictions. Experimental results show that the new algorithm can get the optimal solution with less number of iterations, which greatly saves computation time, and has higher accuracy and better convergence performance. Engineering, computing the shortest distance between the surface and plane of the problem has also been good results, the experimental results are satisfactory.

Effects of a Native Ant, Pristomyrmex pungens (Hymenoptera: Formicidae) on the Population Dynamics and Spatial Distribution of the Invasive Mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

The mealybug Phenacoccus solenopsis has been recently reported as a serious invasive insect pest in China. Earlier investigations suggest that some species of native ants may tend P solenopsis in the field, and affect the population number and spatial distribution of P solenopsis. To confirm this, we studied the relationship between P solenopsis and the native ant Pristomyrmex pungens on Dendranthema morifolium plants in a garden spot. We found there was a significant positive correlation between population numbers of P solenopsis and P pungens, and the less the distance from nest, the greater the quantity of P solenopsis. Additionally, the mean number of P solenopsis increased significantly in the presence of P pungens. P solenopsis and P pungens had strong crowding tendencies and these individuals were attracted to each other on all investigated dates except on August 6. Our results suggest the presence of P pungens has effects on the population numbers and spatial distribution of P solenopsis on D. morifolium plants, and this relationship between them may have an important effect on the population explosion and dispersal of the invasive mealybug.

Crowding by a repeating pattern

Theinability to recognize a peripheral target among flankers is called crowding. For a foveal target, crowding can be distinguished from overlap masking by its sparing of detection, linear scaling with eccentricity, and invariance with target size.Crowding depends on the proximity and similarity of the flankers to the target. Flankers that are far from or dissimilar to the target do not crowd it. On a gray page, text whose neighboring letters have different colors, alternately black and white, has enough dissimilarity that it might escape crowding. Since reading speed is normally limited by crowding, escape from crowding should allow faster reading. Yet reading speed is unchanged (Chung & Mansfield, 2009). Why? A recent vernier study found that using alternating-color flankers produces strong crowding (Manassi, Sayim, & Herzog, 2012). Might that effect occur with letters and reading? Critical spacing is the minimum center-to-center target-flanker spacing needed to correctly identify the target. We measure it for a target letter surrounded by several equidistant flanker letters of the same polarity, opposite polarity, or mixed polarity: alternately white and black. We find strong crowding in the alternating condition, even though each flanker letter is beyond its own critical spacing (as measured in a separate condition). Thus a periodic repeating pattern can produce crowding even when the individual elements do not. Further, in all conditions we find that, once a periodic pattern repeats (two cycles), further repetition does not affect critical spacing of the innermost flanker.

Crowding, grouping, timing

In crowding, target perception is deteriorated by flanking elements. For example, when a vernier is flanked by two lines of the same length, vernier offset discrimination strongly deteriorates. Interestingly, changing the color of the flankers can reduce crowding (uncrowding). Similarly, when the flanking lines are part of a cube, i.e., a good Gestalt, crowding is weak. Conversely, however, scrambling the lines of the cubes, i.e., a “bad” Gestalt, leads to strong crowding. We proposed that crowding is strong when target and flankers group (two-lines, scrambled cubes). Crowding is weak when the target ungroups from the flankers (two flanking lines with different color, cubes). Here, we show, first, that when target and flankers group (strong crowding), crowding is unaffected by stimulus duration. Two same-length flankers presented for 20 ms lead to similar performance as when presented for 150 ms. Second, in uncrowding with flankers of different color (and other basic feature differences), performance is again unaffected by stimulus duration. Third, in uncrowding with cubes, duration matters. For short durations (20 ms), crowding is strong and only for longer stimulus durations (from 120 ms on) does crowding decrease. We suggest that, for short durations, the brain cannot process the good Gestalt of the cubes. The representation of the cube’s lines is “unstructured”, as in the scrambled cubes, and hence crowding is strong. Interestingly, a short preview (20 ms duration) of only the cubes strongly reduces crowding, even when the preview is presented one second before the “crowded” stimulus. Our results suggest that uncrowding emerges in a slow, recurrent manner, with iconic memory playing an important role.

Bionic Intelligent Optimization Algorithm Based on MMAS and Fish-Swarm Algorithm

With large number of ants, the ant colony algorithm would always take a long time or is rather difficult to find the optimal path from complex chapter path, further more, there exists a contradiction between stagnation, accelerated convergence and precocity. In this paper, we propose a new bionic optimization algorithm. The main idea of the algorithm is to introduce the horizons concept in the MMAS fish swarm algorithm, so it would take shorter time to find the optimal path with numerous ants, and the introduction of the concept of fish swarm algorithm congestion level would enable the ant colony find the path of global optimization with a strong crowding limit which avoids the emergence of local extreme and improves the accuracy and efficiency of the algorithm. DOI: http://dx.doi.org/10.11591/telkomnika.v11i9.2952

Grouping and crowding affect target appearance over different spatial scales.

Crowding is the impairment of peripheral target perception by nearby flankers. A number of recent studies have shown that crowding shares many features with grouping. Here, we investigate whether effects of crowding and grouping on target perception are related by asking whether they operate over the same spatial scale. A target letter T had two sets of flanking Ts of varying orientations. The first set was presented close to the target, yielding strong crowding. The second set was either close enough to cause crowding on their own or too far to cause crowding on their own. The Ts of the second set had the same orientation that either matched the target’s orientation (Grouped condition) or not (Ungrouped condition). In Experiment 1, the Grouped flankers reduced crowding independently of their distance from the target, suggesting that grouping operated over larger distances than crowding. In Experiments 2 and 3 we found that grouping did not affect sensitivity but produced a strong bias to report that the grouped orientation was present at the target location whether or not it was. Finally, we investigated whether this bias was a response or perceptual bias, rejecting the former in favor of a perceptual grouping explanation. We suggest that the effect of grouping is to assimilate the target to the identity of surrounding flankers when they are all the same, and that this shape assimilation effect differs in its spatial scale from the integration effect of crowding.

Interletter spacing and dyslexia

Zorzi et al. (1) reported in PNAS that enlarging interletter spacing increases reading speed and accuracy in dyslexic readers. They attributed this to an abnormally strong crowding effect. An important question here is whether or not these effects are, in fact, specific to dyslexia. Zorzi et al. (1) sought to examine this by including a control group. Based on the results from this group, they concluded “... that increased crowding is most likely a fundamental deficit in dyslexia....” We make two observations.

Improved electrode performance in gallium nitride LEDs

Light-emitting diodes based on III-nitride semiconductors have made their way into applications such as backlighting for displays, and solid-state white lighting. High-power LEDs with efficacies larger than conventional fluorescent lamps are now commercially available, bringing the world closer toward the realization of energy-efficient solid-state lighting.1, 2 However, despite significant breakthroughs in light extraction and internal quantum efficiencies, the formation of low resistance, transparent ohmic contact to the highly resistive p-GaN (gallium nitride) layer continues to be a challenge.3 Modern commercial LEDs employ either translucent nickel-gold or indium tin oxide (ITO) as a transparent conductive electrode. Nevertheless, the low transparency of a nickel-gold stack—as well as increasing concerns over the soaring prices and future demand for indium—have initiated a search for an alternative material.4 In addition, next-generation LEDs require transparent conductive electrodes to be flexible (unlike ITO, which is brittle), cheap, and compatible with large-scale manufacturing methods. Graphene, the most recently discovered form of carbon, offers exceptional characteristics such as high transparency, mechanical flexibility, and superior thermal and electrical conductivities.5, 6 Despite its comparatively high sheet resistance (Rs/, recent work has shown that graphene can be applied to the p-GaN layer in GaN-based LEDs as a transparent conductive electrode in place of ITO.7 However, because of the large difference in work function (ˆ), integrating pristine graphene directly with p-GaN forms a Schottky barrier height (SBH, q®B ) at the interface. A large SBH is undesirable because it can create low contact resistance, which leads to strong current crowding and a high operating voltage. Figure 1.Ultraviolet photoelectron spectra of pristine and doped—with 10 and 20mM solutions of gold (III) chloride (AuCl3)—multilayer graphene (MLG) films. The inset bar diagram shows the variation in work function versus AuCl3 concentration. a.u.: Arbitrary units.

Saccadic selection and crowding in visual search: stronger lateral masking leads to shorter search times

We investigated the role of crowding in saccadic selection during visual search. To guide eye movements, often information from the visual periphery is used. Crowding is known to deteriorate the quality of peripheral information. In four search experiments, we studied the role of crowding, by accompanying individual search elements by flankers. Varying the difference between target and flankers allowed us to manipulate crowding strength throughout the stimulus. We found that eye movements are biased toward areas with little crowding for conditions where a target could be discriminated peripherally. Interestingly, for conditions in which the target could not be discriminated peripherally, this bias reversed to areas with strong crowding. This led to shorter search times for a target presented in areas with stronger crowding, compared to a target presented in areas with less crowding. These findings suggest a dual role for crowding in visual search. The presence of flankers similar to the target deteriorates the quality of the peripheral target signal but can also attract eye movements, as more potential targets are present over the area.

Crowding Out Informal Care? Evidence from a Field 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.