Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 6.265
Filtrar
1.
Invest Ophthalmol Vis Sci ; 60(13): 4109-4119, 2019 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-31574139

RESUMO

Purpose: We measure neural responses associated with form and motion processing in children with anisometropia before and after treatment with spectacles and occlusion. Methods: In this prospective, case-control treatment study, 10 children with anisometropia and amblyopia and 16 age-matched visually normal children participated. Steady-state visual evoked potentials (VEP) were recorded from electrodes over the occipital cortex. The visual stimulus comprised a horizontal bar grating into which Vernier offsets were introduced and withdrawn periodically at 3.75 Hz. The VEP amplitude at 3.75 Hz (first harmonic [1F]) and 7.5 Hz (second harmonic [2F]) were recorded to index the sensitivity of form/position-sensitive versus motion/transient-sensitive neural populations, respectively. Response amplitude at 1F and 2F were recorded over a series of 10 logarithmically spaced offset sizes before and after treatment. Main outcome measures are VEP amplitude versus displacement functions, interocular response amplitude differences. Results: After relaxing into spectacles (minimally-treated state), form/position-sensitive responses in the dominant/less ametropic eye of the children with anisometropia were larger and responses in the more ametropic eye were smaller than those of controls. Motion-transient responses were equal to those of controls in the less ametropic eye, but were smaller than controls in the more ametropic eye. After treatment, responses did not differ from those of controls. Conclusions: Form and motion responses are differentially susceptible to neural deprivation via optical blur. Form responses are more plastic than motion responses in minimally-treated children with anisometropic amblyopia. Most treatment effects occurred above threshold range, suggesting some treatment effects are not detected clinically.


Assuntos
Ambliopia/fisiopatologia , Anisometropia/fisiopatologia , Óculos , Percepção de Forma/fisiologia , Percepção de Movimento/fisiologia , Ambliopia/reabilitação , Anisometropia/reabilitação , Estudos de Casos e Controles , Criança , Pré-Escolar , Potenciais Evocados Visuais , Feminino , Humanos , Masculino , Estudos Prospectivos , Acuidade Visual , Córtex Visual/fisiologia
2.
PLoS Comput Biol ; 15(10): e1007398, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31626643

RESUMO

Despite the complexity of the visual world, humans rarely confuse variations in illumination, for example shadows, from variations in material properties, such as paint or stain. This ability to distinguish illumination from material edges is crucial for determining the spatial layout of objects and surfaces in natural scenes. In this study, we explore the role that color (chromatic) cues play in edge classification. We conducted a psychophysical experiment that required subjects to classify edges into illumination and material, in patches taken from images of natural scenes that either contained or did not contain color information. The edge images were of various sizes and were pre-classified into illumination and material, based on inspection of the edge in the context of the whole image from which the edge was extracted. Edge classification performance was found to be superior for the color compared to grayscale images, in keeping with color acting as a cue for edge classification. We defined machine observers sensitive to simple image properties and found that they too classified the edges better with color information, although they failed to capture the effect of image size observed in the psychophysical experiment. Our findings are consistent with previous work suggesting that color information facilitates the identification of material properties, transparency, shadows and the perception of shape-from-shading.


Assuntos
Percepção de Cores/fisiologia , Percepção Visual/fisiologia , Adulto , Cor , Sensibilidades de Contraste/fisiologia , Sinais (Psicologia) , Feminino , Percepção de Forma/fisiologia , Humanos , Iluminação , Masculino , Reconhecimento Visual de Modelos/fisiologia , Estimulação Luminosa/métodos , Psicofísica
3.
J Vis ; 19(11): 6, 2019 09 03.
Artigo em Inglês | MEDLINE | ID: mdl-31509602

RESUMO

Considerable uncertainty remains regarding the types of features human vision uses for shape representation. Visual-search experiments are reported which assessed the hypothesis of a surface-based (i.e., edge-bounded polygons) code for shape representation in human vision. The results indicate slower search rates and/or longer response times when the target shape shares its constituent surfaces with distractors (conjunction condition) than when the target surfaces are unique in the display (nonconjunction condition). This demonstration is made using test conditions that strictly control any potential artifact pertaining to target-distractor similarity. The surface-based code suggested by this surface-conjunction effect is strictly 2-D, since the effect occurs even when the surfaces are shared between the target and distractors in the 2-D image but not in their 3-D instantiation. Congruently, this latter finding is unaltered by manipulations of the richness of the depth information offered by the stimuli. It is proposed that human vision uses a 2-D surface-based code for shape representation which, considering other key findings in the field, probably coexists with an alternative representation mode based on a type of structural description that can integrate information pertaining to the 3-D aspect of shapes.


Assuntos
Percepção de Forma/fisiologia , Percepção Visual/fisiologia , Adolescente , Adulto , Feminino , Humanos , Masculino , Mascaramento Perceptivo/fisiologia , Estimulação Luminosa , Tempo de Reação/fisiologia , Adulto Jovem
4.
Psychon Bull Rev ; 26(5): 1641-1649, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31485909

RESUMO

One way to better understand how animals visually perceive their environment is to assess the way in which visual information is interpreted and adapted based on preconceptions. Domestic dogs represent a unique species in which to evaluate visual perception as recent findings suggest they may differ from humans and other animal species in terms of their susceptibility to geometric visual illusions. Dogs have demonstrated human-like, reversed, and null susceptibility depending on the type of illusion. To further evaluate how dogs perceive their environment, it is necessary to perform additional assessments of visual perception. One such assessment is the perceptual filling-in of figures, which may be invoked when presented with illusory contours. Six dogs were assessed on their perception of the Ehrenstein illusory contour illusion in a two-choice size-discrimination task. Dogs, as a group, demonstrated equivocal perception of illusory contours. Some individual dogs, however, demonstrated human-like perception of the subjective contours, providing preliminary evidence that this species is capable of perceiving illusory contour illusions, thereby improving the current understanding of canine visual perception capabilities. Additional assessments using alternative illusory contour illusions are needed to clarify these results and identify features that underpin the individual differences observed.


Assuntos
Cães/fisiologia , Percepção de Forma/fisiologia , Ilusões/fisiologia , Ilusões Ópticas/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Animais , Animais Domésticos
5.
J Vis ; 19(9): 3, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31390466

RESUMO

The visual system can represent multiple objects in a compressed form of ensemble summary statistics (such as object numerosity, mean, and feature variance/range). Yet the relationships between the different types of visual statistics remain relatively unclear. Here, we tested whether two summaries (mean and numerosity, or mean and range) are calculated independently from each other and in parallel. Our participants performed dual tasks requiring a report about two summaries in each trial, and single tasks requiring a report about one of the summaries. We estimated trial-by-trial correlations between the precision of reports as well as correlations across observers. Both analyses showed the absence of correlations between different types of ensemble statistics, suggesting their independence. We also found no decrement (except that related to the order of report explained by memory retrieval) in performance in dual compared to single tasks, which suggests that two statistics of one ensemble can be processed in parallel.


Assuntos
Percepção de Forma/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Vias Visuais/fisiologia , Adulto , Algoritmos , Análise de Variância , Biometria , Feminino , Humanos , Masculino , Adulto Jovem
6.
Invest Ophthalmol Vis Sci ; 60(10): 3374-3380, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31387113

RESUMO

Purpose: Binocular discordance due to strabismus, anisometropia, or both may result in not only monocular visual acuity deficits, but also in motion perception deficits. We determined the prevalence of fellow-eye deficits in motion-defined form (MDF) perception, the ability to identify a two-dimensional (2D) shape defined by motion rather than luminance contrast. We also examined the following: the causative role of reduced visual acuity and binocularity, associations with clinical and sensory factors, and effectiveness of binocular amblyopia treatment in alleviating deficits. Methods: Participants included 91 children with residual amblyopia (strabismic, anisometropic, or both; age, 9.0 ± 1.7 years), 79 nonamblyopic children with treated strabismus or anisometropia (age, 8.5 ± 2.1 years), and 20 controls (age, 8.6 ± 1.5 years). MDF coherence thresholds, visual acuity, stereoacuity, and interocular suppression were measured. Results: MDF deficits, relative to controls, were present in the fellow eye of 23% of children with residual amblyopia and 20% of nonamblyopic children. Stereoacuity and age first patched were correlated with MDF threshold (r = 0.29, 95% CI: 0.09-0.47; r = -0.33, 95% CI: -0.13 to -0.50, respectively). MDF deficits were more common in children treated with patching alone than in those receiving contrast-rebalanced binocular treatment with games or movies (t89 = 3.46; P = 0.0008). The latter was associated with a reduction in mean fellow eye MDF threshold (t26 = 6.32, P < 0.0001). Conclusions: Fellow eye MDF deficits are common and likely reflect abnormalities in binocular cortical mechanisms that result from early discordant visual experience. Binocular amblyopia treatment, which is effective in improving amblyopic eye visual acuity, appears to provide a benefit for the fellow eye.


Assuntos
Ambliopia/fisiopatologia , Percepção de Movimento/fisiologia , Transtornos da Percepção/fisiopatologia , Visão Binocular/fisiologia , Ambliopia/terapia , Anisometropia/fisiopatologia , Bandagens , Criança , Feminino , Percepção de Forma/fisiologia , Humanos , Masculino , Estrabismo/fisiopatologia , Jogos de Vídeo , Acuidade Visual
7.
Psychol Aging ; 34(6): 805-820, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31414857

RESUMO

In hybrid foraging tasks, observers search visual displays, so called patches, for multiple instances of any of several types of targets with the goal of collecting targets as quickly as possible. Here, targets were photorealistic objects. Younger and older adults collected targets by mouse clicks. They could move to the next patch whenever they decided to do so. The number of targets held in memory varied between 8 and 64 objects, and the number of items (targets and distractors) in the patches varied between 60 and 105 objects. Older adults foraged somewhat less efficiently than younger adults due to a more exploitative search strategy. When target items became depleted in a patch and search slowed down, younger adults acted according to the optimal foraging theory and moved on to the next patch when the instantaneous rate of collection was close to their average rate of collection. Older adults, by contrast, were more likely to stay longer and spend time searching for the last few targets. Within a patch, both younger and older adults tended to collect the same type of target in "runs." This behavior is more efficient than continual switching between target types. Furthermore, after correction for general age-related slowing, RT × set size functions revealed largely preserved attention and memory functions in older age. Hybrid foraging tasks share features with important real-world search tasks. Differences between younger and older observers on this task may therefore help to explain age differences in many complex search tasks of daily life. (PsycINFO Database Record (c) 2019 APA, all rights reserved).


Assuntos
Envelhecimento , Atenção/fisiologia , Envelhecimento Cognitivo , Percepção de Forma/fisiologia , Memória de Curto Prazo/fisiologia , Memória , Reconhecimento Visual de Modelos/fisiologia , Percepção Visual/fisiologia , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Vida , Masculino , Pessoa de Meia-Idade , Motivação , Estimulação Luminosa/métodos , Tempo de Reação , Adulto Jovem
8.
Neural Netw ; 119: 113-138, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31404805

RESUMO

Behavioral and neural data suggest that visual attention spreads along contour segments to bind them into a unified object representation. Such attentional labeling segregates the target contour from distractors in a process known as mental contour tracing. A recurrent competitive map is developed to simulate the dynamics of mental contour tracing. In the model, local excitation opposes global inhibition and enables enhanced activity to propagate on the path offered by the contour. The extent of local excitatory interactions is modulated by the output of the multi-scale contour detection network, which constrains the speed of activity spreading in a scale-dependent manner. Furthermore, an L-junction detection network enables tracing to switch direction at the L-junctions, but not at the X- or T-junctions, thereby preventing spillover to a distractor contour. Computer simulations reveal that the model exhibits a monotonic increase in tracing time as a function of the distance to be traced. Also, the speed of tracing increases with decreasing proximity to the distractor contour and with the reduced curvature of the contours. The proposed model demonstrated how an elaborated version of the winner-takes-all network can implement a complex cognitive operation such as contour tracing.


Assuntos
Atenção , Percepção de Forma , Estimulação Luminosa/métodos , Pensamento , Atenção/fisiologia , Simulação por Computador , Percepção de Forma/fisiologia , Humanos , Pensamento/fisiologia
9.
J Vis ; 19(9): 1, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31369042

RESUMO

Behavioral studies in humans indicate that peripheral vision can do object recognition to some extent. Moreover, recent studies have shown that some information from brain regions retinotopic to visual periphery is somehow fed back to regions retinotopic to the fovea and disrupting this feedback impairs object recognition in human. However, it is unclear to what extent the information in visual periphery contributes to human object categorization. Here, we designed two series of rapid object categorization tasks to first investigate the performance of human peripheral vision in categorizing natural object images at different eccentricities and abstraction levels (superordinate, basic, and subordinate). Then, using a delayed foveal noise mask, we studied how modulating the foveal representation impacts peripheral object categorization at any of the abstraction levels. We found that peripheral vision can quickly and accurately accomplish superordinate categorization, while its performance in finer categorization levels dramatically drops as the object presents further in the periphery. Also, we found that a 300-ms delayed foveal noise mask can significantly disturb categorization performance in basic and subordinate levels, while it has no effect on the superordinate level. Our results suggest that human peripheral vision can easily process objects at high abstraction levels, and the information is fed back to foveal vision to prime foveal cortex for finer categorizations when a saccade is made toward the target object.


Assuntos
Percepção de Forma/fisiologia , Fóvea Central/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Campos Visuais/fisiologia , Adulto , Feminino , Humanos , Masculino
10.
J Vis ; 19(9): 2, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31369043

RESUMO

Objects have a variety of different features that can be represented as probability distributions. Recent findings show that in addition to mean and variance, the visual system can also encode the shape of feature distributions for features like color or orientation. In an odd-one-out search task we investigated observers' ability to encode two feature distributions simultaneously. Our stimuli were defined by two distinct features (color and orientation) while only one was relevant to the search task. We investigated whether the irrelevant feature distribution influences learning of the task-relevant distribution and whether observers also encode the irrelevant distribution. Although considerable learning of feature distributions occurred, especially for color, our results also suggest that adding a second irrelevant feature distribution negatively affected the encoding of the relevant one and that little learning of the irrelevant distribution occurred. There was also an asymmetry between the two different features: Searching for the oddly oriented target was more difficult than searching for the oddly colored target, which was reflected in worse learning of the color distribution. Overall, the results demonstrate that it is possible to encode information about two feature distributions simultaneously but also reveal considerable limits to this encoding.


Assuntos
Percepção de Cores/fisiologia , Percepção de Forma/fisiologia , Aprendizagem/fisiologia , Orientação Espacial/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Adulto , Análise de Variância , Atenção/fisiologia , Feminino , Humanos , Masculino , Adulto Jovem
11.
Elife ; 82019 07 12.
Artigo em Inglês | MEDLINE | ID: mdl-31298655

RESUMO

The human visual system is tasked with recovering the different physical sources of optical structure that generate our retinal images. Separate research has focused on understanding how the visual system estimates (a) environmental sources of image structure and (b) blur induced by the eye's limited focal range, but little is known about how the visual system distinguishes environmental sources from optical defocus. Here, we present evidence that this is a fundamental perceptual problem and provide insights into how and when the visual system succeeds and fails in solving it. We show that fully focused surface shading can be misperceived as defocused and that optical blur can be misattributed to the material properties and shape of surfaces. We further reveal how these misperceptions depend on the relationship between shading gradients and sharp contours, and conclude that computations of blur are inherently linked to computations of surface shape, material, and illumination.


Assuntos
Percepção de Forma/fisiologia , Percepção Visual/fisiologia , Humanos , Fenômenos Ópticos , Estimulação Luminosa
12.
J Vis ; 19(7): 5, 2019 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-31287859

RESUMO

The visual system must organize dynamic input into useful percepts across time, balancing between stability and sensitivity to change. The temporal integration window (TIW) has been hypothesized to underlie this balance: If two or more stimuli fall within the same TIW, they are integrated into a single percept; those that fall in different windows are segmented (Arnett & Di Lollo, 1979; Wutz, Muschter, van Koningsbruggen, Weisz, & Melcher, 2016). Visual TIWs have been studied in adults, showing average windows of 65 ms (Wutz et al., 2016); however, it is unclear how windows develop through early childhood. Here we measured TIWs in 5- to 7-year-old children and adults, using a variant of the missing dot task (Di Lollo, 1980; Wutz et al. 2016), in which integration and segmentation thresholds were measured within the same participant, using the same stimuli. Participants saw a sequence of two displays separated by an interstimulus interval (ISI) that determined the visibility of a visual search target. Longer ISIs increased the likelihood of detecting a segmentation target (but decreased detection for the integration target) although shorter ISIs increased the likelihood of detecting the integration target (but decreased detection of the segmentation target). We could then estimate the TIW by measuring the point at which these two functions intersect. Children's TIWs (M = 68 ms) were comparable to adults' (M = 73 ms) with no appreciable age trend within our sample, indicating that TIWs reach adult levels by approximately 5 years of age.


Assuntos
Percepção do Tempo/fisiologia , Percepção Visual/fisiologia , Adulto , Estudos de Casos e Controles , Criança , Pré-Escolar , Feminino , Percepção de Forma/fisiologia , Humanos , Masculino , Percepção de Movimento/fisiologia , Estimulação Luminosa , Tempo de Reação/fisiologia , Fatores de Tempo , Adulto Jovem
13.
J Exp Psychol Hum Percept Perform ; 45(10): 1304-1318, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31282695

RESUMO

Curvature along a contour is important for shape perception, and a special role may be played by points of maxima (extrema) along the contour. Angles are discontinuities in curvature, a special case at one extreme of the curvature continuum. We report 4 studies using abstract shapes and comparing polygons (curvature discontinuities at the vertices) and a smoothed version of polygons (no vertices). Polygons are simpler and are defined by a small set of vertices, whereas smoothed shapes have a continuous curvature change along the contour. Angles have also been discussed as an early signal of threat and danger, and on that basis, one may predict faster responses to polygons. However, curved shapes are more typical of the natural environment in which the visual system has evolved. For a detection task, we found faster responses to smooth shapes, not mediated by complexity (Experiment 1). We then tested 3 orthogonal shape tasks: comparison between shapes (detection of repetition; Experiment 2a), comparison after a rotation (Experiment 2b), and detection of bilateral symmetry (Experiment 3). In all tasks, responses for smoothed stimuli were faster; there was also an interaction with type of response: Trials with smooth shapes were faster when a positive response was produced. Overall, there was evidence that smooth shapes with continuous change in curvature along the contour are processed more efficiently, and they tend to be classified as targets. We discuss this in relation to shape analysis and to the preference for smoothed over angular shapes. (PsycINFO Database Record (c) 2019 APA, all rights reserved).


Assuntos
Comportamento de Escolha/fisiologia , Percepção de Forma/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Tempo de Reação/fisiologia , Adulto , Percepção de Cores/fisiologia , Feminino , Humanos , Masculino , Desempenho Psicomotor/fisiologia , Adulto Jovem
14.
J Vis ; 19(7): 1, 2019 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-31260515

RESUMO

We make a rich variety of judgments on faces, but the underlying features are poorly understood. Here we describe a challenging geographical-origin classification problem that elucidates feature representations in both humans and machine algorithms. In Experiment 1, we collected a diverse set of 1,647 faces from India labeled with their fine-grained geographical origin (North vs. South India), characterized the categorization performance of 129 human subjects on these faces, and compared this with the performance of machine vision algorithms. Our main finding is that while many machine algorithms achieved an overall performance comparable to that of humans (64%), their error patterns across faces were qualitatively different despite training. To elucidate the face parts used by humans for classification, we trained linear classifiers on overcomplete sets of features derived from each face part. This revealed mouth shape to be the most discriminative part compared to eyes, nose, or external contour. In Experiment 2, we confirmed that humans relied the most on mouth shape for classification using an additional experiment in which subjects classified faces with occluded parts. In Experiment 3, we compared human performance for briefly viewed faces and for inverted faces. Interestingly, human performance on inverted faces was predicted better by computational models compared to upright faces, suggesting that humans use relatively more generic features on inverted faces. Taken together, our results show that studying hard classification tasks can lead to useful insights into both machine and human vision.


Assuntos
Face , Adolescente , Adulto , Algoritmos , Simulação por Computador , Reconhecimento Facial/fisiologia , Feminino , Percepção de Forma/fisiologia , Humanos , Índia/etnologia , Masculino , Pessoa de Meia-Idade , Adulto Jovem
15.
Acta Psychol (Amst) ; 198: 102870, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31301573

RESUMO

The standard visual search task is integral to the study of selective attention and in search tasks target present slopes are the primary index of attentional demand. However, there are times when similarities in slopes may obscure important differences between conditions. To demonstrate this point, we used the case of line-ending illusory contours, building on a study by Li, Cave, and Wolfe (2008) where orientation-based search for figures defined by line-ending illusory contours was compared to that for the corresponding real-contour controls. Consistent with Li et al. (2008), we found search to be efficient for both illusory contour figures and the corresponding real-contour controls, with no significant differences between them. However, major differences between illusory contours and the real-contour controls emerged in selective enumeration, a task where participants enumerated targets in a display of distractors, with the number of targets and distractors manipulated. When looking at the distractor slopes, the increase in RT to enumerate a single target as a function of the number of distractors (a direct analogue to target present trials, with identical displays), we found distractor costs for illusory contour figures to be over 100 ms/distractor higher than for the corresponding real-contour controls. Furthermore, the discrepancies in RT slope between 1-3 and 6-8 targets associated with subitizing were only seen in the real-contour controls. These results show that similarities in RT slopes in search may mask important differences between conditions that emerge in other tasks.


Assuntos
Percepção de Forma/fisiologia , Ilusões/psicologia , Reconhecimento Visual de Modelos/fisiologia , Desempenho Psicomotor/fisiologia , Adolescente , Atenção/fisiologia , Feminino , Previsões , Humanos , Ilusões/fisiologia , Masculino , Orientação/fisiologia , Estimulação Luminosa/métodos , Distribuição Aleatória , Adulto Jovem
16.
J Exp Psychol Hum Percept Perform ; 45(9): 1248-1264, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31219282

RESUMO

Visual search is the task of finding things with uncertain locations. Despite decades of research, the features that guide visual search remain poorly specified, especially in realistic contexts. This study tested the role of two features-shape and orientation-both in the presence and absence of hue information. We conducted five experiments to describe preview-target mismatch effects, decreases in performance caused by differences between the image of the target as it appears in the preview and as it appears in the actual search display. These mismatch effects provide direct measures of feature importance, with larger performance decrements expected for more important features. Contrary to previous conclusions, our data suggest that shape and orientation only guide visual search when color is not available. By varying the probability of mismatch in each feature dimension, we also show that these patterns of feature guidance do not change with the probability that the previewed feature will be invalid. We conclude that the target representations used to guide visual search are much less precise than previously believed, with participants encoding and using color and little else. (PsycINFO Database Record (c) 2019 APA, all rights reserved).


Assuntos
Percepção de Cores/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Percepção Espacial/fisiologia , Adulto , Feminino , Percepção de Forma/fisiologia , Humanos , Masculino , Adulto Jovem
17.
J Vis ; 19(6): 14, 2019 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-31194220

RESUMO

Humans can estimate and encode numerosity over a large range, from very few items to several hundreds. Two distinct mechanisms have been proposed: subitizing, for numbers up to four and estimation for larger numerosities. We have recently extended this idea by suggesting that for very densely packed arrays, when items are less segregable, a third "texture" mechanism comes into play. In this study, we provide further evidence for the existence of a third regime for numerosity. Reaction times were very low in the subitizing range, rising rapidly for numerosities greater than four. However, for tightly packed displays of very high numerosities, reaction times became faster. These results reinforce the idea of three regimes in the processing of numerosity, subitizing, estimation, and texture.


Assuntos
Percepção de Forma/fisiologia , Percepção de Movimento/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Tempo de Reação/fisiologia , Adulto , Feminino , Humanos , Masculino
18.
J Vis ; 19(6): 5, 2019 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-31173630

RESUMO

Scene viewing is used to study attentional selection in complex but still controlled environments. One of the main observations on eye movements during scene viewing is the inhomogeneous distribution of fixation locations: While some parts of an image are fixated by almost all observers and are inspected repeatedly by the same observer, other image parts remain unfixated by observers even after long exploration intervals. Here, we apply spatial point process methods to investigate the relationship between pairs of fixations. More precisely, we use the pair correlation function, a powerful statistical tool, to evaluate dependencies between fixation locations along individual scanpaths. We demonstrate that aggregation of fixation locations within 4° is stronger than expected from chance. Furthermore, the pair correlation function reveals stronger aggregation of fixations when the same image is presented a second time. We use simulations of a dynamical model to show that a narrower spatial attentional span may explain differences in pair correlations between the first and the second inspection of the same image.


Assuntos
Movimentos Oculares/fisiologia , Fixação Ocular/fisiologia , Modelos Estatísticos , Adolescente , Adulto , Atenção , Feminino , Percepção de Forma/fisiologia , Humanos , Masculino , Memória de Longo Prazo/fisiologia , Probabilidade , Adulto Jovem
19.
J Vis ; 19(6): 6, 2019 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-31173631

RESUMO

A representation of shape that is low dimensional and stable across minor disruptions is critical for object recognition. Computer vision research suggests that such a representation can be supported by the medial axis-a computational model for extracting a shape's internal skeleton. However, few studies have shown evidence of medial axis processing in humans, and even fewer have examined how the medial axis is extracted in the presence of disruptive contours. Here, we tested whether human skeletal representations of shape reflect the medial axis transform (MAT), a computation sensitive to all available contours, or a pruned medial axis, which ignores contours that may be considered "noise." Across three experiments, participants (N = 2062) were shown complete, perturbed, or illusory two-dimensional shapes on a tablet computer and were asked to tap the shapes anywhere once. When directly compared with another viable model of shape perception (based on principal axes), participants' collective responses were better fit by the medial axis, and a direct test of boundary avoidance suggested that this result was not likely because of a task-specific cognitive strategy (Experiment 1). Moreover, participants' responses reflected a pruned computation in shapes with small or large internal or external perturbations (Experiment 2) and under conditions of illusory contours (Experiment 3). These findings extend previous work by suggesting that humans extract a relatively stable medial axis of shapes. A relatively stable skeletal representation, reflected by a pruned model, may be well equipped to support real-world shape perception and object recognition.


Assuntos
Simulação por Computador , Percepção de Forma/fisiologia , Visão Ocular/fisiologia , Humanos
20.
J Vis ; 19(6): 2, 2019 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-31166580

RESUMO

People are able to perceive the 3D shape of illuminated surfaces using image shading cues. Theories about how we accomplish this often assume that the human visual system estimates a single lighting direction and interprets shading cues in accord with that estimate. In natural scenes, however, lighting can be much more complex than this, with multiple nearby light sources. Here we show that the human visual system can successfully judge 3D surface shape even when the lighting direction varies from place to place over a surface, provided the scale at which these lighting changes occur is similar to, or larger than, the size of the shape features being judged. Furthermore, we show that despite being able to accommodate rapid changes in lighting direction when judging shape, observers are generally unable to detect these changes. We conclude that, rather than relying on a single estimated illumination direction, the human visual system can accommodate illumination that varies substantially and rapidly across a surface.


Assuntos
Percepção de Forma/fisiologia , Iluminação , Feminino , Humanos , Imagem Tridimensional , Masculino , Estimulação Luminosa/métodos , Adulto Jovem
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA