Naturalistic Images Research Articles

Computational luminance constancy from naturalistic images.

The human visual system supports stable percepts of object color even though the light that reflects from object surfaces varies significantly with the scene illumination. To understand the computations that support stable color perception, we study how estimating a target object's luminous reflectance factor (LRF; a measure of the light reflected from the object under a standard illuminant) depends on variation in key properties of naturalistic scenes. Specifically, we study how variation in target object reflectance, illumination spectra, and the reflectance of background objects in a scene impact estimation of a target object's LRF. To do this, we applied supervised statistical learning methods to the simulated excitations of human cone photoreceptors, obtained from labeled naturalistic images. The naturalistic images were rendered with computer graphics. The illumination spectra of the light sources and the reflectance spectra of the surfaces in the scene were generated using statistical models of natural spectral variation. Optimally decoding target object LRF from the responses of a small learned set of task-specific linear receptive fields that operate on a contrast representation of the cone excitations yields estimates that are within 13% of the correct LRF. Our work provides a framework for evaluating how different sources of scene variability limit performance on luminance constancy.

The reliability of attentional biases for emotional images measured using a free-viewing eye-tracking paradigm.

Cognitive theories of anxiety disorders and depression posit that attentional biases play a role in the development, maintenance, and recurrence of these disorders. Several paradigms have been used to examine attentional biases in anxiety and depression, but information on the reliability of different attentional bias indices is limited. In this study we examined the internal consistency and 6-month test-retest reliability of attentional bias indices derived from a free-viewing eye-tracking paradigm. Participants completed two versions of an eye-tracking task-one that used naturalistic images as stimuli, and one that used face images. In both tasks, participants viewed displays of four images, each display consisting of one threat image, one sad image, one positive/happy image, and one neutral image. The internal consistency of the fixation indices (dwell time and number of fixations) for threat, sad, and positive images over the full 8-s display was moderate to excellent. When the 8-s display was divided into 2-s intervals, the dwell times for the 0- to 2-s and 2- to 4-s intervals showed lower reliability, particularly for the face images. The attentional bias indices for the naturalistic images showed adequate to good stability over the test-retest period, whereas the test-retest reliability estimates for the face images were in the low to moderate range. The implications of these results for attentional bias research are discussed.

Adaptation Aftereffects in the Perception of Crabs and Lobsters as Examples of Complex Natural Objects.

To recognize a familiar object, incoming perceptual information is matched against object representations in memory. Mounting evidence suggests that these representations are not stable, but adapt flexibly to recently encountered perceptual information. This is evident in the form of aftereffects, where prolonged exposure to one object (adaptor) influences perception of the next (test stimulus). So far, adaptation aftereffects have been mainly shown for human faces and simple geometric shapes, and it has been concluded that face aftereffects partially derive from shape adaptation. However, it is largely unknown whether adaptation aftereffects generalize to other categories of complex, naturalistic biological objects, and if so, whether these effects can be explained by shape adaptation. To answer these questions, we conducted three experiments in which images of crabs and lobsters were presented in two versions: as complex, naturalistic images, or reduced to their simplified geometric shapes. In Experiment 1, we found robust adaptation aftereffects for the complex versions of the images, indicating that adaptation aftereffects generalize to animate objects other than faces. Experiment 2 showed adaptation aftereffects for the simplified stimuli, replicating previous findings on geometric shapes. Experiment 3 demonstrated that adaptation to the simplified animal shapes results in aftereffects on the complex naturalistic stimuli. Comparisons between experiments revealed that aftereffects were largest in the first experiment, in which complex stimuli served as adaptor and test stimuli. Together, these experiments show that the magnitude of adaptation aftereffects depends on the complexity of the adaptor, but not on that of the test stimuli, and that shape adaptation plays a role in – but cannot entirely account for – the object aftereffects.

Contextual modulation of sensitivity to naturalistic image structure in macaque V2.

The stimulus selectivity of neurons in V1 is well known, as is the finding that their responses can be affected by visual input to areas outside of the classical receptive field. Less well understood are the ways selectivity is modified as signals propagate to visual areas beyond V1, such as V2. We recently proposed a role for V2 neurons in representing the higher order statistical dependencies found in images of naturally occurring visual texture. V2 neurons, but not V1 neurons, respond more vigorously to “naturalistic” images that contain these dependencies than to “noise” images that lack them. In this work, we examine the dependency of these effects on stimulus size. For most V2 neurons, the preference for naturalistic over noise stimuli was modest when presented in small patches and gradually strengthened with increasing size, suggesting that the mechanisms responsible for this enhanced sensitivity operate over regions of the visual field that are larger than the classical receptive field. Indeed, we found that surround suppression was stronger for noise than for naturalistic stimuli and that the preference for large naturalistic stimuli developed over a delayed time course consistent with lateral or feedback connections. These findings are compatible with a spatially broad facilitatory mechanism that is absent in V1 and suggest that a distinct role for the receptive field surround emerges in V2 along with sensitivity for more complex image structure.NEW & NOTEWORTHY The responses of neurons in visual cortex are often affected by visual input delivered to regions of the visual field outside of the conventionally defined receptive field, but the significance of such contextual modulations are not well understood outside of area V1. We studied the importance of regions beyond the receptive field in establishing a novel form of selectivity for the statistical dependencies contained in natural visual textures that first emerges in area V2.

The brain's representations may be compatible with convolution-based memory models.

Convolution is a mathematical operation used in vector-models of memory that have been successful in explaining a broad range of behaviour, including memory for associations between pairs of items, an important primitive of memory upon which a broad range of everyday memory behaviour depends. However, convolution models have trouble with naturalistic item representations, which are highly auto-correlated (as one finds, e.g., with photographs), and this has cast doubt on their neural plausibility. Consequently, modellers working with convolution have used item representations composed of randomly drawn values, but introducing so-called noise-like representation raises the question how those random-like values might relate to actual item properties. We propose that a compromise solution to this problem may already exist. It has also long been known that the brain tends to reduce auto-correlations in its inputs. For example, centre-surround cells in the retina approximate a Difference-of-Gaussians (DoG) transform. This enhances edges, but also turns natural images into images that are closer to being statistically like white noise. We show the DoG-transformed images, although not optimal compared to noise-like representations, survive the convolution model better than naturalistic images. This is a proof-of-principle that the pervasive tendency of the brain to reduce auto-correlations may result in representations of information that are already adequately compatible with convolution, supporting the neural plausibility of convolution-based association-memory. (PsycINFO Database Record

Vergence driven accommodation with simulated disparity in myopia and emmetropia

The formation of focused and corresponding foveal images requires a close synergy between the accommodation and vergence systems. This linkage is usually decoupled in virtual reality systems and may be dysfunctional in people who are at risk of developing myopia. We study how refractive error affects vergence-accommodation interactions in stereoscopic displays. Vergence and accommodative responses were measured in 21 young healthy adults (n=9 myopes, 22–31 years) while subjects viewed naturalistic stimuli on a 3D display. In Step 1, vergence was driven behind the monitor using a blurred, non-accommodative, uncrossed disparity target. In Step 2, vergence and accommodation were driven back to the monitor plane using naturalistic images that contained structured depth and focus information from size, blur and/or disparity. In Step 1, both refractive groups converged towards the stereoscopic target depth plane, but the vergence-driven accommodative change was smaller in emmetropes than in myopes (F1,19=5.13, p=0.036). In Step 2, there was little effect of peripheral depth cues on accommodation or vergence in either refractive group. However, vergence responses were significantly slower (F1,19=4.55, p=0.046) and accommodation variability was higher (F1,19=12.9, p=0.0019) in myopes. Vergence and accommodation responses are disrupted in virtual reality displays in both refractive groups. Accommodation responses are less stable in myopes, perhaps due to a lower sensitivity to dioptric blur. Such inaccuracies of accommodation may cause long-term blur on the retina, which has been associated with a failure of emmetropization.

Facial First Impressions of Partner Preference Traits: Trustworthiness, Status, and Attractiveness

This research used the minimal exposure paradigm to examine facial first impressions of traits of trustworthiness, status, and attractiveness, considered important in verbal models of partner preferences. Heterosexual participants rated opposite-sex faces comprising either naturalistic images or youthful-looking averaged faces on trustworthiness, status, and attractiveness following 33, 100, and 500 ms masked presentation. The pattern masks were phase scrambled to provide the same overall color composition, brightness, and spatial frequency content as the presented faces. Trustworthiness, status, and attractiveness judgments were all reliable at above-chance levels even at 33 ms presentation, and extra time (100 or 500 ms) only led to modest improvement in the correspondence with an independent set of time-unconstrained judgments. The increasing prevalence of online images and internet-based relationships make these findings timely and important.

The other-race effect in face learning: Using naturalistic images to investigate face ethnicity effects in a learning paradigm.

The other-race effect in face identification has been reported in many situations and by many different ethnicities, yet it remains poorly understood. One reason for this lack of clarity may be a limitation in the methodologies that have been used to test it. Experiments typically use an old-new recognition task to demonstrate the existence of the other-race effect, but such tasks are susceptible to different social and perceptual influences, particularly in terms of the extent to which all faces are equally individuated at study. In this paper we report an experiment in which we used a face learning methodology to measure the other-race effect. We obtained naturalistic photographs of Chinese and Caucasian individuals, which allowed us to test the ability of participants to generalize their learning to new ecologically valid exemplars of a face identity. We show a strong own-race advantage in face learning, such that participants required many fewer trials to learn names of own-race individuals than those of other-race individuals and were better able to identify learned own-race individuals in novel naturalistic stimuli. Since our methodology requires individuation of all faces, and generalization over large image changes, our finding of an other-race effect can be attributed to a specific deficit in the sensitivity of perceptual and memory processes to other-race faces.

FMRI with Central Vision Loss: Effects of Fixation Locus and Stimulus Type.

In patients with central visual field scotomata, a large part of visual cortex is not adequately stimulated. Patients often use a new eccentric fixation area on intact peripheral retina ("preferred retinal locus"-PRL) that functions as a pseudo-fovea. We used functional magnetic resonance imaging (fMRI) to examine whether stimulating this pseudo-fovea leads to increased activation or altered activation patterns in visual cortex in comparison to stimulating a comparable peripheral area in the opposite hemifield (OppPRL). Nineteen patients with binocular central scotomata caused by hereditary retinal dystrophies and an age-matched control group were tested. The center of the visual field, PRL, and OppPRL were stimulated with flickering checkerboard stimuli and object pictures during fMRI measurement. Results show that stimulation with pictures of everyday objects led to overall larger BOLD (blood oxygen level dependent) responses in visual cortex compared to that evoked by stimulation with flickering checkerboards. Patients showed this enhancement as early as in V1. When the PRL was directly stimulated with object pictures, the central representation area in early visual cortex was coactivated in the patients but not in the controls. In higher visual areas beyond retinotopic cortex, BOLD responses to stimulation of the PRL with object pictures were significantly enhanced in comparison to stimulation of the OppPRL area. Highly stable eccentric fixation with the PRL was associated with a higher BOLD signal in visual cortex in patients, and this effect was most pronounced in the conditions with object picture stimulation. The observed results suggest that naturalistic images are more likely to trigger top-down processes that regulate activation in early visual cortex in patients with central vision loss.

Perceptual and neural deficits in processing naturalistic image structure in amblyopia

Perceptual and neural deficits in processing naturalistic image structure in amblyopia

Objective Measurement of Fusional Vergence Ranges and Heterophoria in Infants and Preschool Children

PurposeBinocular alignment typically includes motor fusion compensating for heterophoria. This study evaluated heterophoria and then accommodation and vergence responses during measurement of fusional ranges in infants and preschoolers.MethodsPurkinje image eye tracking and eccentric photorefraction (MCS PowerRefractor) were used to record the eye alignment and accommodation of uncorrected infants (n = 17; 3–5 months old), preschoolers (n = 19; 2.5–5 years), and naïve functionally emmetropic adults (n = 14; 20–32 years; spherical equivalent [SE], +1 to −1 diopters [D]). Heterophoria was derived from the difference between monocular and binocular alignments while participants viewed naturalistic images at 80 cm. The presence or absence of fusion was then assessed after base-in (BI) and base-out (BO) prisms (2–40 prism diopters [pd]) were introduced.ResultsMean (±SD) SE refractions were hyperopic in infants (+2.4 ± 1.2 D) and preschoolers (+1.1 ± 0.6 D). The average exophoria was similar (P = 0.11) across groups (Infants, −0.79 ± 2.5 pd; Preschool, −2.43 ± 2.0 pd; Adults, −1.0 ± 2.7 pd). Mean fusional vergence range also was similar (P = 0.1) for BI (Infants, 11.2 ± 2.5 pd; Preschool, 8.8 ± 2.8 pd; Adults, 11.8 ± 5.2 pd) and BO (Infants, 14 ± 6.6 pd; Preschool, 15.3 ± 8.3 pd; Adults, 20 ± 9.2 pd). Maximum change in accommodation to the highest fusible prism was positive (increased accommodation) for BO (Infants, 1.69 ± 1.4 D; Preschool, 1.35 ± 1.6 D; Adults, 1.22 ± 1.0 D) and negative for BI (Infants, −0.96 ± 1.0 D; Preschool, −0.78 ± 0.6 D; Adults, −0.62 ± 0.3 D), with a similar magnitude across groups (BO, P = 0.6; BI, P = 0.4).ConclusionsDespite typical uncorrected hyperopia, infants and preschoolers exhibited small exophorias at 80 cm, similar to adults. All participants demonstrated substantial fusional ranges, providing evidence that even 3- to 5-month-old infants can respond to a large range of image disparities.

A Dialogue with Abraham Uyovbisere's Semi-Nude Figures

A Dialogue with Abraham Uyovbisere's Semi-Nude Figures Kenechi Uzoamaka ANASO Abstract Abraham Uyovbisere has been labelled a feminist for making numerous naturalistic images of females (Akintunde-Johnson 1989, Njoagwu, 1993). A good number of his paintings are semi nude representations of the female and are therefore covered from the waist downwards leaving the upper body completely bare. This raises questions about why an artist who has been publicly regarded as a feminist makes such images. Furthermore, it is necessary to ascertain whether the paintings in question validate or reinforce feministic ideals. Given that Freud established that the natural human is prone to distortions and censorship of original intentions (Richards, 1973), Shank and Tilley's (1987) proposed method of "decent ring" the artist from the analysis of his work was used in the critical and contextual analyses of randomly selected semi nude paintings. Feminist positions on female imagery formed the interpretive context. The results of the analyses revealed that Abraham Uyovbisere employs the wrap to serve euphemistic purposes in his semi-nude female representations. It was also observed that when viewed from the feministic standpoint, the semi-nude paintings are objectified images of the female gender and are therefore an affront to feminism. Full Text: PDF DOI: 10.15640/ijaah.v4n1a5

A shifting sense of human scale: Tracing ‘deep time’ aspects of modern depiction

The affective status of the material world as it pertains to the historical development of human cognition and activity lies at the centre of the current discourse of cognitive archaeology. Through applications of ‘enactive’ conceptions of mind the notion of a human mind that imposes its will upon an inert material world is being challenged by recognising how the mind emerges through the material engagement of an embodied subject that is always coupled to an affective material world. The active role played by materials in the development of cognition reveals a dynamic entwining of mind and matter across past spatiotemporal trajectories that positions human artefacts as a trace of such an entwining. There are two central point's drawn from this context that are important for the discussion within this paper: firstly, the significance of the development of human perceptual experience and cognition that is relational to the material world; secondly how a more focussed study of human perception reveals how the material world itself (its status and meaning) emerges as relational to human experience. The emergence of the concept of ‘deep geological time’ during the nineteenth century will be used as an object of study in which the idea of geological deep time (its theory and its continued development) emerges alongside, and shapes, an historically contingent perceptual experience that itself plays an active role in the very shaping of the idea of geological deep time. This emergent relationship will be made more tangible through an art historical iconological study of a range of visual artefacts — artistic and naturalistic images of deep time — during this period readable through the changes and transformations of certain stylistic and compositional strategies used to depict human figures within the works.

The (In)Effectiveness of Simulated Blur for Depth Perception in Naturalistic Images.

We examine depth perception in images of real scenes with naturalistic variation in pictorial depth cues, simulated dioptric blur and binocular disparity. Light field photographs of natural scenes were taken with a Lytro plenoptic camera that simultaneously captures images at up to 12 focal planes. When accommodation at any given plane was simulated, the corresponding defocus blur at other depth planes was extracted from the stack of focal plane images. Depth information from pictorial cues, relative blur and stereoscopic disparity was separately introduced into the images. In 2AFC tasks, observers were required to indicate which of two patches extracted from these images was farther. Depth discrimination sensitivity was highest when geometric and stereoscopic disparity cues were both present. Blur cues impaired sensitivity by reducing the contrast of geometric information at high spatial frequencies. While simulated generic blur may not assist depth perception, it remains possible that dioptric blur from the optics of an observer’s own eyes may be used to recover depth information on an individual basis. The implications of our findings for virtual reality rendering technology are discussed.

A higher order visual neuron tuned to the spatial amplitude spectra of natural scenes.

Animal sensory systems are optimally adapted to those features typically encountered in natural surrounds, thus allowing neurons with limited bandwidth to encode challengingly large input ranges. Natural scenes are not random, and peripheral visual systems in vertebrates and insects have evolved to respond efficiently to their typical spatial statistics. The mammalian visual cortex is also tuned to natural spatial statistics, but less is known about coding in higher order neurons in insects. To redress this we here record intracellularly from a higher order visual neuron in the hoverfly. We show that the cSIFE neuron, which is inhibited by stationary images, is maximally inhibited when the slope constant of the amplitude spectrum is close to the mean in natural scenes. The behavioural optomotor response is also strongest to images with naturalistic image statistics. Our results thus reveal a close coupling between the inherent statistics of natural scenes and higher order visual processing in insects.

What is a clear picture? Human sensitivity to noise in naturalistic images.

What is a clear picture? Human sensitivity to noise in naturalistic images.

Stereoscopic Offset Makes Objects Easier to Recognize.

Binocular vision is obviously useful for depth perception, but it might also enhance other components of visual processing, such as image segmentation. We used naturalistic images to determine whether giving an object a stereoscopic offset of 15-120 arcmin of crossed disparity relative to its background would make the object easier to recognize in briefly presented (33-133 ms), temporally masked displays. Disparity had a beneficial effect across a wide range of disparities and display durations. Most of this benefit occurred whether or not the stereoscopic contour agreed with the object’s luminance contour. We attribute this benefit to an orienting of spatial attention that selected the object and its local background for enhanced 2D pattern processing. At longer display durations, contour agreement provided an additional benefit, and a separate experiment using random-dot stimuli confirmed that stereoscopic contours plausibly contributed to recognition at the longer display durations in our experiment. We conclude that in real-world situations binocular vision confers an advantage not only for depth perception, but also for recognizing objects from their luminance patterns and bounding contours.

Learning Slowness in a Sparse Model of Invariant Feature Detection.

Primary visual cortical complex cells are thought to serve as invariant feature detectors and to provide input to higher cortical areas. We propose a single model for learning the connectivity required by complex cells that integrates two factors that have been hypothesized to play a role in the development of invariant feature detectors: temporal slowness and sparsity. This model, the generative adaptive subspace self-organizing map (GASSOM), extends Kohonen's adaptive subspace self-organizing map (ASSOM) with a generative model of the input. Each observation is assumed to be generated by one among many nodes in the network, each being associated with a different subspace in the space of all observations. The generating nodes evolve according to a first-order Markov chain and generate inputs that lie close to the associated subspace. This model differs from prior approaches in that temporal slowness is not an externally imposed criterion to be maximized during learning but, rather, an emergent property of the model structure as it seeks a good model of the input statistics. Unlike the ASSOM, the GASSOM does not require an explicit segmentation of the input training vectors into separate episodes. This enables us to apply this model to an unlabeled naturalistic image sequence generated by a realistic eye movement model. We show that the emergence of temporal slowness within the model improves the invariance of feature detectors trained on this input.

On the number of perceivable blur levels in naturalistic images

Blur is a useful cue for depth. Natural images contain objects at a range of depths whose depth can be signaled by their perceived blur. Here, to evaluate the usefulness of blur as a depth cue, we estimate the number blur levels that observers can perceive simultaneously. To estimate this value, observers discriminated and classified dead leaves patterns that contained a controlled distribution of blur levels but are more complex or naturalistic than stimuli typically used in blur research. We used a 2-IFC discrimination task, in which observers reported the interval that contained more blur levels and a classification task, in which observers reported the number of perceived blur levels. In both tasks, observers could not discriminate or classify more than four levels of blur in the stimulus reliably. In isolation from other cues, blur may provide only a coarse cue to depth and add limited depth information when present in natural scenes with complex distributions of blur and multiple depth cues.

A Procedure for Selecting Naturalistic Images Based on Appleton’s Theory

A Procedure for Selecting Naturalistic Images Based on Appleton’s Theory