Contrast and depth perception: effects of texture contrast and area contrast

Difficult at dusk? Illuminating the debate on cricket ball visibility

OBJECTIVES

Investigate the visibility of new and old red, white and pink cricket balls under lighting and background conditions experienced during a day-night cricket match.

DESIGN

We modelled the luminance contrast signals available for a typical observer for a ball against backgrounds in a professional cricket ground, at different times of day.

METHODS

Spectral reflectance (light reflected as a function of wavelength) was derived from laboratory measurements of new and old red, white and pink balls. We also gathered spectral measurements from backgrounds (pitch, grass, sightscreens, crowd, sky) and spectral illuminance during a day-night match (natural afternoon light, through dusk to night under floodlights) from Lord's Cricket Ground (London, UK). The luminance contrast of the ball relative to the background was calculated for each combination of ball, time of day, and background surface.

RESULTS

Old red and old pink balls may offer little or no contrast against the grass, pitch and crowd. New pink balls can also be of low contrast against the crowd at dusk, as can pink and white balls (of any age) against the sky at dusk.

CONCLUSIONS

Reports of difficulties with visibility of the pink ball are supported by our data. However, our modelling also shows that difficulties with visibility may also be expected under certain circumstances for red and white balls. The variable conditions in a cricket ground and the changing colour of an ageing ball make maintaining good visibility of the ball a challenge when playing day-night matches.

Depth Correction of 3D NanoSIMS Images Shows Intracellular Lipid and Cholesterol Distributions while Capturing the Effects of Differential Sputter Rate

Knowledge of the distributions of drugs, metabolites, and drug carriers within cells is a prerequisite for the development of effective disease treatments. Intracellular component distribution may be imaged with high sensitivity and spatial resolution by using a NanoSIMS in the depth profiling mode. Depth correction strategies that capture the effects of differential sputtering without requiring additional measurements could enable producing accurate 3D NanoSIMS depth profiling images of intracellular component distributions. Here we describe an approach for depth correcting 3D NanoSIMS depth profiling images of cells that accounts for differential sputter rates. Our approach uses the secondary ion and secondary electron depth profiling images to reconstruct the cell's morphology at every raster plane. These cell morphology reconstructions are used to adjust the z-positions and heights of the voxels in the component-specific 3D NanoSIMS images. We validated this strategy using AFM topography data and reconstructions created from depth profiling images acquired with focused ion beam-secondary electron microscopy. Good agreement was found for the shapes and relative heights of the reconstructed morphologies. Application of this depth correction strategy to 3D NanoSIMS depth profiling images of a metabolically labeled cell better resolved the transport vesicles, organelles, and organellar membranes containing ¹⁸O-cholesterol and ¹⁵N-sphingolipids. Accurate 3D NanoSIMS images of intracellular component distributions may now be produced without requiring correlated analyses with separate instruments or the assumption of a constant sputter rate. This will allow visualization of the subcellular distributions of lipids, metabolites, drugs, and nanoparticles in 3D, information pivotal to understanding and treating disease.

Depth correction of 3D NanoSIMS images using secondary electron pixel intensities

Strategies that do not require additional characterization to be performed on the sample or the collection of additional secondary ion signals are needed to depth correct 3D SIMS images of cells. Here, we develop a depth correction strategy that uses the pixel intensities in the secondary electron images acquired during negative-ion NanoSIMS depth profiling to reconstruct the sample morphology. This morphology reconstruction was then used to depth correct the 3D SIMS images that show the components of interest in the sample. As a proof of concept, we applied this approach to NanoSIMS depth profiling data that show the 15N-enrichment and 18O-enrichment from 15N-sphingolipids and 18O-cholesterol, respectively, within a metabolically labeled Madin-Darby canine kidney cell. Comparison of the cell morphology reconstruction to the secondary electron images collected with the NanoSIMS revealed that the assumption of a constant sputter rate produced small inaccuracies in sample morphology after approximately 0.66 μm of material was sputtered from the cell. Nonetheless, the resulting 3D renderings of the lipid-specific isotope enrichments better matched the shapes and positions of the subcellular compartments that contained 15N-sphingolipids and 18O-cholesterol than the uncorrected 3D SIMS images. This depth correction of the 3D SIMS images also facilitated the detection of spherical cholesterol-rich compartments that were surrounded by membranes containing cholesterol and sphingolipids. Thus, we expect this approach will facilitate identifying the subcellular structures that are enriched with biomolecules of interest in 3D SIMS images while eliminating the need for correlated analyses or additional secondary ion signals for the depth correction of 3D NanoSIMS images.

Pedestrians Accept Shorter Distances to Light Vehicles Than Dark Ones When Crossing the Street

Does the brightness of an approaching vehicle affect a pedestrian's crossing decision? Thirty participants indicated their street-crossing intentions when facing approaching light or dark vehicles. The experiment was conducted in a real daylight environment and, additionally, in a corresponding virtual one. A real road with actual cars provides high face validity, while a virtual environment ensures the scenario's precise reproducibility and repeatability for each participant. In both settings, participants judged dark vehicles to be a more imminent threat-either closer or moving faster-when compared with light ones. Secondary results showed that participants accepted a significantly shorter time-to-contact when crossing the street in the virtual setting than on the real road.

Visual Behavior Impairments as an Aberrant Sensory Processing in the Mouse Model of Fragile X Syndrome

Fragile X Syndrome (FXS), the most common inherited form of human intellectual disability (ID) associated with autistic-like behaviors, is characterized by dys-sensitivity to sensory stimuli, especially vision. In the absence of Fragile Mental Retardation Protein (FMRP), both retinal and cerebral structures of the visual pathway are impaired, suggesting that perception and integration of visual stimuli are altered. However, behavioral consequences of these defects remain unknown. In this study, we used male Fmr1^−/y mice to further define visual disturbances from a behavioral perspective by focusing on three traits characterizing visual modality: perception of depth, contrasts and movements. We performed specific tests (Optomotor Drum, Visual Cliff) to evaluate these visual modalities, their evolution from youth to adulthood, and to assess their involvement in a cognitive task. We show that Fmr1^−/y mice exhibit alteration in their visual skills, displaying impaired perspective perception, a drop in their ability to understand a moving contrasted pattern, and a defect in contrasts discrimination. Interestingly, Fmr1^−/y phenotypes remain stable over time from adolescence to late adulthood. Besides, we report that color and shape are meaningful for the achievement of a cognitive test involving object recognition. Altogether, these results underline the significance of visual behavior alterations in FXS conditions and relevance of assessing visual skills in neuropsychiatric models before performing behavioral tasks, such as cognitive assessments, that involve visual discrimination.

Which Attribute of Ceiling Color Influences Perceived Room Height?

OBJECTIVE

We investigate effects of the hue, saturation, and luminance of ceiling color on the perceived height of interior spaces.

BACKGROUND

Previous studies have reported that the perceived height of an interior space is influenced by the luminance of the ceiling, but not by the luminance contrast between ceiling and walls: brighter ceilings appeared higher than darker ceilings, irrespective of wall and floor luminance. However, these studies used solely achromatic colors. We report an experiment in which we extend these findings to effects of chromatic ceiling colors.

METHODS

We presented stereoscopic room simulations on a head-mounted display (Oculus Rift DK2) and varied hue (red, green, blue), saturation (low, high), and luminance (bright, dark) of the ceiling independently of each other.

RESULTS

We found the previously reported ceiling luminance effect to apply also to chromatic colors: subjects judged brighter ceilings to be higher than darker ceilings. The remaining color dimensions merely had a very small (hue) or virtually no effect (saturation) on perceived height.

CONCLUSION

In order to maximize the perceived height of an interior space, we suggest painting the ceiling in the brightest possible color. The hue and saturation of the paint are only of minor importance.

APPLICATION

The present study improves the empirical basis for interior design guidelines regarding effects of surface color on the perceived layout of interior spaces.

Optical illusions and life-threatening traffic crashes: A perspective on aerial perspective

Aerial perspective illusion is a feature of visual perception where landscapes appear relatively close in clear light and distant in dim light. We hypothesized that bright sunlight might cause drivers to perceive distant terrain as relatively close and misinterpret the approach speed of surrounding landscape as unduly slow. This hypothesis would mean, in turn, that drivers in bright sunlight may underestimate their progress on the road, compensate by traveling at a faster baseline speed, and ultimately increase the prevailing risk of a life-threatening traffic crash. We conducted three pilot studies to illustrate how the illusion might contribute to a life- threatening traffic crash. The first illustration used a questionnaire to demonstrate that most respondents were mistaken when judging the distance between simple balls in different positions. The second illustration involved an experimental manipulation to assess whether aerial perspective influenced judgments about the relative positions of vehicles in traffic. The third illustration analyzed a segment of high-volume fast-speed traffic and found an increased frequency of speeding under bright sunlight. Together with past work based on the visual arts, these examples illustrate how an aerial perspective illusion can affect distance perception, may appear in realistic traffic situations, and could potentially contribute to the risk of a life-threatening traffic crash. An awareness of this hypothesis might lead to applications on how optical illusions could extend to everyday traffic and might potentially inform safety warnings to prevent life- threatening crashes.

Life-threatening motor vehicle crashes in bright sunlight

Bright sunlight may create visual illusions that lead to driver error, including fallible distance judgment from aerial perspective. We tested whether the risk of a life-threatening motor vehicle crash was increased when driving in bright sunlight.This longitudinal, case-only, paired-comparison analysis evaluated patients hospitalized because of a motor vehicle crash between January 1, 1995 and December 31, 2014. The relative risk of a crash associated with bright sunlight was estimated by evaluating the prevailing weather at the time and place of the crash compared with the weather at the same hour and location on control days a week earlier and a week later.The majority of patients (n = 6962) were injured during daylight hours and bright sunlight was the most common weather condition at the time and place of the crash. The risk of a life-threatening crash was 16% higher during bright sunlight than normal weather (95% confidence interval: 9-24, P < 0.001). The increased risk was accentuated in the early afternoon, disappeared at night, extended to patients with different characteristics, involved crashes with diverse features, not apparent with cloudy weather, and contributed to about 5000 additional patient-days in hospital. The increased risk extended to patients with high crash severity as indicated by ambulance involvement, surgical procedures, length of hospital stay, intensive care unit admission, and patient mortality. The increased risk was not easily attributed to differences in alcohol consumption, driving distances, or anomalies of adverse weather.Bright sunlight is associated with an increased risk of a life-threatening motor vehicle crash. An awareness of this risk might inform driver education, trauma staffing, and safety warnings to prevent a life-threatening motor vehicle crash.

LEVEL OF EVIDENCE

Epidemiologic Study, level III.

Temporal evolution of pattern disparity processing in humans

Stereo matching, i.e., the matching by the visual system of corresponding parts of the images seen by the two eyes, is inherently a 2D problem. To gain insights into how this operation is carried out by the visual system, we measured, in human subjects, the reflexive vergence eye movements elicited by the sudden presentation of stereo plaids. We found compelling evidence that the 2D pattern disparity is computed by combining disparities first extracted within orientation selective channels. This neural computation takes 10-15 ms, and is carried out even when subjects perceive not a single plaid but rather two gratings in different depth planes (transparency). However, we found that 1D disparities are not always effectively combined: when spatial frequency and contrast of the gratings are sufficiently different pattern disparity is not computed, a result that cannot be simply attributed to the transparency of such stimuli. Based on our results, we propose that a narrow-band implementation of the IOC (Intersection of Constraints) rule (Fennema and Thompson, 1979; Adelson and Movshon, 1982), preceded by cross-orientation suppression, underlies the extraction of pattern disparity.

Fashion versus perception: the impact of surface lightness on the perceived dimensions of interior space

OBJECTIVES

We compare expert opinion with perceptual judgment regarding the influence of color on the perceived height and width of interior rooms.

BACKGROUND

We hypothesize that contrary to popular belief, ceiling and wall lightness have additive effects on perceived height, whereas the lightness contrast between these surfaces is less important. We assessed the intuitions of architectural experts as to which surface colors maximize apparent height and compared these intuitions with psychophysical height and width estimates for rooms differing in ceiling, floor, and wall lightness.

METHOD

Experiment 1 was a survey of architectural experts and nonexperts. Experiments 2 and 3 presented virtual rooms varying in physical height, physical width, and surface lightness.

RESULTS

In Experiment 1, both experts and nonexperts erroneously assumed that the lightness contrast between ceiling and walls influences perceived height Experiment 2 showed that the lightness contrast does not determine apparent height but that ceiling and wall lightness have additive effects. Experiment 3 demonstrated a decrease in perceived width with physical height, whereas the perceived height was not related to physical width. Apparent width was unaffected by ceiling lightness.

CONCLUSION

Light ceiling and light walls make a room appear higher, whereas floor color has a weaker effect. We also found evidence for an asymmetric interaction between height and width.

APPLICATION

The question of how to color walls and ceiling to maximize the apparent size of a room can be answered empirically. Aesthetic considerations may interfere with the correct assessment of the effects of color in experts.

Organização espacial na percepção visual de luminosidade

Este estudo analisou a influência de variações físicas dos estímulos, com base na organização espacial de figura-fundo criada pela associação dos efeitos ilusórios de contraste simultâneo de luminosidade e de contornos subjetivos. A cada participante, no total de 64, foram apresentadas 160 matrizes de escolha, cada uma composta de um estímulo modelo e quatro estímulos de comparação, devendo ser identificado qual dos quatro estímulos de comparação correspondia ao estímulo modelo. A diferença significativa entre as médias de ajuste visual verificadas para a condição de contorno subjetivo médio e para a condição controle (sem contorno) mostrou que a formação clássica de contornos subjetivos de Kanizsa, quando associada ao efeito de contraste simultâneo de luminosidade, influenciou a percepção de luminosidade dos participantes.

Surface lightness influences perceived room height

Surprisingly little scientific research has been conducted on the effects of colour and lightness on the perception of spaciousness. Practitioners and architects typically suggest that a room's ceiling appears higher when it is painted lighter than the walls, while darker ceilings appear lower. Employing a virtual reality setting, we studied the effects of the lightness of different room surfaces on perceived height in two psychophysical experiments. Observers judged the height of rooms varying in physical height as well as in the lightness of ceiling, floor, and walls. Experiment 1 showed the expected increase of perceived height with increases in ceiling lightness. Unexpectedly, the perceived height additionally increased with wall lightness, and the effects of wall lightness and ceiling lightness were roughly additive, incompatible with a simple effect of the lightness contrast between the ceiling and the walls. Experiment 2 demonstrated that the floor lightness has no significant effect on perceived height, and that the total brightness of the room is not the critical factor influencing the perceived height. Neither can the results be explained by previously reported effects of brightness on apparent depth or perceived distance.

Using Blur to Affect Perceived Distance and Size

We present a probabilistic model of how viewers may use defocus blur in conjunction with other pictorial cues to estimate the absolute distances to objects in a scene. Our model explains how the pattern of blur in an image together with relative depth cues indicates the apparent scale of the image's contents. From the model, we develop a semiautomated algorithm that applies blur to a sharply rendered image and thereby changes the apparent distance and scale of the scene's contents. To examine the correspondence between the model/algorithm and actual viewer experience, we conducted an experiment with human viewers and compared their estimates of absolute distance to the model's predictions. We did this for images with geometrically correct blur due to defocus and for images with commonly used approximations to the correct blur. The agreement between the experimental data and model predictions was excellent. The model predicts that some approximations should work well and that others should not. Human viewers responded to the various types of blur in much the way the model predicts. The model and algorithm allow one to manipulate blur precisely and to achieve the desired perceived scale efficiently.