The influence of depth segmentation on colour constancy

In real scenes, surfaces in different depth planes often differ in the luminance and chromatic content of their illumination. Scene segmentation is therefore an important issue when considering the compensation of illumination changes in our visual perception (lightness and colour constancy). Chromatic adaptation is an important sensory component of colour constancy and has been shown to be linked to the two-dimensional spatial structure of a scene (Werner, 2003 Vision Research 43 1611 - 1623). Here, the question is posed whether this cooperation also extends to the organisation of a scene in depth. The influence of depth on colour constancy was tested by introducing stereo disparity, whereby the test patch and background were perceived in either the same or one of five different depth planes (1.9-57 min of arc). There were no additional cues to depth such as shadows or specular highlights. For consistent illumination changes, colour constancy was reduced when the test patch and background were separated in depth, indicating a reduction of contextual influences. An interaction was found between the influences of stereo depth and spatial frequency on colour constancy. In the case of an inconsistent illumination change, colour constancy was reduced if the test patch and background were in the same depth plane (2-D condition), but not if they were separated in depth (3-D condition). Furthermore, colour constancy was slightly better in the 3-D inconsistent condition than in the 2-D inconsistent condition. It is concluded that depth segmentation supports colour constancy in scenes with inconsistent illumination changes. Processes of depth segmentation are implemented at an early sensory stage of colour constancy, and they define visual regions within which the effects of illuminant changes are discounted for separately. The results support recent models that posit such implementation of scene segmentation in colour constancy.     

Measurement invariance of WISC-IV across normative and clinical samples

Measurement invariance of the WISC-IV second-order factorial structure between normative and clinical samples was investigated using WISC-IV core subtests and a total of 1100 children aged 6-16. Multi-group higher order analysis of mean and covariance structure (MG-MACS) models were used to analyze these data. Results supported measurement invariance. Only Coding and Comprehension subtest intercepts varied slightly between groups. The hypothesized WISC-IV factor model described the data well. Factor patterns, first- and second-order factor loadings, intercepts, residual variances of measured subtests, and disturbances of first-order factors of the WISC-IV were generally invariant. Results suggested that WISC-IV index scores and subtests have the same meaning for children in both normative and clinical groups.     

Measurement invariance tests of the Impression Management sub-scale of the Balanced Inventory of Desirable Responding

The Impression Management (IM) subscale of the Balanced Inventory of Desirable Responding (Paulhus, 1988) has been used as a proxy for common method variance in anonymous settings and as a cause of faking on personality testing in confidential settings. This study uses confirmatory factor analysis to conduct measurement invariance/equivalence tests (also known as multiple group analysis) on the IM subscale in a quasi-experiment in anonymous and confidential data collection settings. Using Brown’s (2006) bottom-up approach to Cheung and Rensvold’s (1999) model testing steps and Cheung and Rensvold’s (2002) statistical tests, the IM sub-scale was determined to have equal form, equal factor loadings, equal indicator error variances, equal factor variance, and an equal factor covariance in both 1-factor and 2-factor models in both data collection settings. Mean scale scores were significantly higher in the confidential group than in the anonymous group. These results suggest that using the IM sub-scale as a cause of faking and as a proxy for common method variance (CMV) is likely to be acceptable because the psychometric properties of the instrument are invariant across testing conditions.     

Colour vision brings clarity to shadows

We have revealed a new role for colour vision in visual scene analysis: colour vision facilitates shadow identification. Shadows are important features of the visual scene, providing information about the shape, depth, and movement of objects. To be useful for perception, however, shadows must be distinguished from other types of luminance variation, principally the variation in object reflectance. A potential cue for distinguishing shadows from reflectance variations is colour, since chromatic changes typically occur at object but not shadow boundaries. We tested whether colour cues were exploited by the visual system for shadow identification, by comparing the ability of human test subjects to identify simulated shadows on chromatically variegated versus achromatically variegated backgrounds with identical luminance compositions. Performance was superior with the chromatically variegated backgrounds. Furthermore, introducing random colour contrast across the shadow boundaries degraded their identification. These findings demonstrate that the visual system exploits inbuilt assumptions about the relationships between colour and luminance in the natural visual world.     

Development of chromatic induction in infancy

The perception of colour in an embedded field is affected by the surround colour. This phenomenon is known as chromatic induction. In the present study we investigated whether the colour perception by infants aged 5–7 months could be affected by the surround colour. In Experiments 1 and 2 each stimulus was composed of an array of six squares in tandem. The colour appearance of the array in the familiarization stimulus was established by chromatic induction. In Experiment 1 we used familiarization stimuli that were perceived as two‐colour array with a two‐colour surround. In Experiment 2 we used a familiarization stimulus that was perceived as a uniform‐colour array with a two‐colour surround. In the test phase, the uniform‐colour array and the two‐colour array were presented on a white uniform‐colour surround in both experiments. The results showed that in Experiment 1 the 5‐ and 7‐month‐old infants had novelty preference for the uniform‐colour test array. This suggested that the infants' colour perception could be affected by surround colour. The results of Experiment 2 showed that the 7‐month‐olds showed a novelty preference for the two‐colour test array, but the 5‐month‐olds showed no novelty preference. This suggested that 7‐month‐olds' colour perception could be affected by surround colour, but that of 5‐month‐olds could not. We discuss the contradiction of the results between Experiments 1 and 2. Copyright © 2007 John Wiley & Sons, Ltd.     

“Filling-in” colour in natural scenes

Our subjective experience of the world as being in full colour across the entire visual field is at odds with the highly fovea-biased distribution of cones in the retina. It is unclear how this percept of “pan-field colour” comes about. We use novel stimuli—“colour chimeras”—to demonstrate a related visual phenomenon in which observers perceive rich colour throughout images with large achromatic regions. This percept appears to critically depend on natural scene statistics. By separately manipulating chromatic and structural content in such images, we demonstrate that both the spatial distribution of colour and the presence of recognizable scene structure contribute to the experience of pan-field colour in these stimuli. Our results suggest that this percept is unlikely to be due to a low-level colour spreading process. Instead, we suggest that mechanisms dependent on natural scenes’ chromatic and luminance statistics provide the basis for the phenomenon.     

The influence of chromatic and achromatic variability on chromatic induction and perceived colour

Judgments of the colour of a surface are influenced by the colour of the surrounding. To determine whether only the average colour of the surrounding matters, or also the chromatic variability, judgments in colourful scenes are often compared with ones in which a target is surrounded by a plain background that provides the same average physical illumination of the retina as the colourful scene. The variability sometimes makes a difference (eg Shevell and Wei, 1998 Vision Research 38 1561-1566), and sometimes it does not (eg Brenner and Cornelissen, 1998 Vision Research 38 1789-1793). Is this because of the nonlinearity in cone responses? We designed scenes that stimulated the cones in an equivalent manner, both on average and in terms of variability, and yet differed markedly in chromatic variability. The more colourful surroundings had considerably less influence on subjects' colour judgments. We conclude that early cone-specific regulation of sensitivity cannot be responsible for the change in perceived colour, and deduce that chromatic induction takes place after contrast gain control.     

Coherent modulation of stimulus colour can affect visually induced self-motion perception

The effects of dynamic colour modulation on vection were investigated to examine whether perceived variation of illumination affects self-motion perception. Participants observed expanding optic flow which simulated their forward self-motion. Onset latency, accumulated duration, and estimated magnitude of the self-motion were measured as indices of vection strength. Colour of the dots in the visual stimulus was modulated between white and red (experiment 1), white and grey (experiment 2), and grey and red (experiment 3). The results indicated that coherent colour oscillation in the visual stimulus significantly suppressed the strength of vection, whereas incoherent or static colour modulation did not affect vection. There was no effect of the types of the colour modulation; both achromatic and chromatic modulations turned out to be effective in inhibiting self-motion perception. Moreover, in a situation where the simulated direction of a spotlight was manipulated dynamically, vection strength was also suppressed (experiment 4). These results suggest that observer's perception of illumination is critical for self-motion perception, and rapid variation of perceived illumination would impair the reliabilities of visual information in determining self-motion.     

Lightness constancy: Ratio invariance and luminance profile

The term simultaneous lightness constancy describes the capacity of the visual system to perceive equal reflecting surfaces as having the same lightness despite lying in different illumination fields. In some cases, however, a lightness constancy failure occurs; that is, equal reflecting surfaces appear different in lightness when differently illuminated. An open question is whether the luminance profile of the illumination edges affects simultaneous lightness constancy even when the ratio invariance property of the illumination edges is preserved. To explore this issue, we ran two experiments by using bipartite illumination displays. Both the luminance profile of an illumination edge and the luminance ratio amplitude between the illumination fields were manipulated. Results revealed that the simultaneous lightness constancy increases when the luminance profile of the illumination edge is gradual (rather than sharp) and homogeneous (rather than inhomogeneous), whereas it decreases when the luminance ratio between the illumination fields is enlarged. The results are interpreted according to the layer decomposition schema, stating that the visual system splits the luminance into perceived lightness and apparent illumination components. We suggest that illumination edges having gradual and homogeneous luminance profiles facilitate the luminance decomposition process, whereas wide luminance ratios impede it.     

Size-distance invariance: Kinetic invariance is different from static invariance

The static form of the size-distance invariance hypothesis asserts that a given proximal stimulus size (visual angle) determines a unique and constant ratio of perceived-object size to perceived object distance. A proposed kinetic invariance hypothesis asserts that a changing proximal stimulus size (an expanding or contracting solid visual angle) produces a constant perceived size and a changing perceived distance such that the instantaneous ratio of perceived size to perceived distance is determined by the instantaneous value of visual angle. The kinetic invariance hypothesis requires a new concept, an operating constraint, to mediate between the proximal expansion or contraction pattern and the perception of rigid object motion in depth. As a consequence of the operating constraint, expansion and contraction patterns are automatically represented in consciousness as rigid objects. In certain static situations, the operation of this constraint produces the anomalous perceived-size-perceived-distance relations called the size-distance paradox.     

Size-distance invariance: kinetic invariance is different from static invariance.

The static form of the size-distance invariance hypothesis asserts that a given proximal stimulus size (visual angle) determines a unique and constant ratio of perceived object size to perceived object distance. A proposed kinetic invariance hypothesis asserts that a changing proximal stimulus size (an expanding or contracting solid visual angle) produces a constant perceived size and a changing perceived distance such that the instantaneous ratio of perceived size to perceived distance is determined by the instantaneous value of visual angle. The kinetic invariance hypothesis requires a new concept, an operating constraint, to mediate between the proximal expansion or contraction pattern and the perception of rigid object motion in depth. As a consequence of the operating constraint, expansion and contraction patterns are automatically represented in consciousness as rigid objects. In certain static situations, the operation of this constraint produces the anomalous perceived-size-perceived-distance relations called the size-distance paradox.     

A checklist for testing measurement invariance

The analysis of measurement invariance of latent constructs is important in research across groups, or across time. By establishing whether factor loadings, intercepts and residual variances are equivalent in a factor model that measures a latent concept, we can assure that comparisons that are made on the latent variable are valid across groups or time. Establishing measurement invariance involves running a set of increasingly constrained structural equation models, and testing whether differences between these models are significant. This paper provides a step-by-step guide to analysing measurement invariance.     

Measurement and structural invariance of parent ratings of ADHD and ODD symptoms across gender for American and Malaysian children

The purpose of this study was to examine the measurement (configural, metric, scalar, and residual) and structural (factor variance, factor covariance, and factor means) invariance of parent ratings of the attention-deficit/hyperactivity disorder - inattention (ADHD-IN), ADHD - hyperactivity/impulsivity (ADHD-HI), and oppositional defiant disorder (ODD) symptoms as described in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) across boys and girls. In an American pediatric sample (N = 1,015) and a Malaysian elementary school-age sample (N = 928), there was strong support for configural, metric, scalar, residual, factor variance, and covariance invariance across gender within each sample. Both American and Malaysian boys had significantly higher scores on the ADHD-IN and ADHD-HI factor means than did girls, whereas only in the American sample did boys score significantly higher on the ODD factor than did girls. The implications of the results for the study of gender, ethnic, and cultural differences associated with ADHD and ODD are discussed.     

Colour vision is aligned with natural scene statistics at 4 months of age

Visual perception in adult humans is thought to be tuned to represent the statistical regularities of natural scenes. For example, in adults, visual sensitivity to different hues shows an asymmetry which coincides with the statistical regularities of colour in the natural world. Infants are sensitive to statistical regularities in social and linguistic stimuli, but whether or not infants’ visual systems are tuned to natural scene statistics is currently unclear. We measured colour discrimination in infants to investigate whether or not the visual system can represent chromatic scene statistics in very early life. Our results reveal the earliest association between vision and natural scene statistics that has yet been found: even as young as 4 months of age, colour vision is aligned with the distributions of colours in natural scenes.

Research Highlights

1. We find infants’ colour sensitivity is aligned with the distribution of colours in the natural world, as it is in adults.
2. At just 4 months, infants’ visual systems are tailored to extract and represent the statistical regularities of the natural world.
3. This points to a drive for the human brain to represent statistical regularities even at a young age.

     

Colour constancy in goldfish and man: influence of surround size and lightness

Colour constancy was investigated by using a series of 10 simultaneously presented surface colours ranging in small steps from green through gray to red-purple. Goldfish were trained to select one medium test field when the entire setup was illuminated with white light. In the tests, either red or green illumination was used. Colour constancy, as inferred from the choice behaviour, was perfect under green illumination when the test fields were presented on a gray or a white background, but imperfect on a black background. Under red illumination and a white background, however, colour constancy was overcompensated. Here, a colour contrast effect was observed. The influence of background lightness was also found when the surround was restricted to a narrow annulus of 4-11 mm width (test field diameter: 14 mm). By applying colour metrics it could be shown that the von Kries coefficient law can describe the overall effect of colour constancy. For an explanation of the effect of surround size and lightness, lateral inhibitory interactions have to be assumed in addition, which are also responsible for simultaneous colour contrast. Very similar results were obtained in experiments with the same colours in human subjects. They had to name the test field appearing 'neutral' under the different illumination and surround conditions, as tested in the goldfish experiment.     

Concave and convex phases in ambiguous figures showing colour shifts. Mach's figure and the AMBEGUJAS phenomenon

Two ambiguous figures (Mach's book-figure and the AMBEGUJAS phenomenon) have been studied. They show colour shifts synchronised with the shifts of their alternative phases. The perceived concave phase appeared to have chromatic surface colour, but the perceived convex phase can appear to be in coloured illumination and shadow (film colour). The two perceived reversible shapes of the Mach figure (the book and the tent) and the three perceived alternative shapes of the Mondrians used in the AMBEGUJAS phenomenon (a roof, a ceiling, and a tile) all can appear to have chromatic surface colours in their concave phases but appear to have coloured illumination and shadow in their convex phases.     

Studying group and time invariance in maximal reliability for multiple‐component measuring instruments via covariance structure modelling

A method for examining invariance in maximal reliability for weighted combinations of congeneric measures is described. The approach is developed within the framework of covariance structure modelling and allows one to ascertain whether a multi‐component instrument consisting of homogeneous measures is associated with the same minimal relative error variance in distinct populations or over time. The procedure yields as a by‐product an interval measure of discrepancy in maximal reliability across independent groups or assessment occasions, and is illustrated with two examples.     

Pigeon pattern perception: limits on perspective invariance

Two experiments are reported in which the response of pigeons to perspective transformations of a pattern target was measured. In the first experiment an alphabet letter was taken as the pattern target (the 'positive') and the response to its perspective transforms was compared to the response to nontarget letters ('negatives') over the course of discrimination training. In the second experiment irregular quadrilaterals were used as positives and the responses to slight perspective deformations of the prototypes were compared to the responses to random transformations of the same magnitude under steady-state conditions. The amount of differential responding depended on the type of transformation. There was no differential response to targets rotated in the picture plane or around the horizontal axis in either experiment. There was differential response to small reductions and enlargements of the target. There was also differential response to translated targets, and this was seen irrespective of the amount of displacement. Results from targets rotated around the vertical axis were erratic, some target-plus-angle combinations elicited differential responding, but most did not. The erratic responses are attributed to symmetries in pattern elements that were abstracted as critical features. Pigeons therefore exhibit no true rotation invariance, limited size invariance, and complete shift invariance. It is argued that size invariance, but not position invariance, may depend on prior exposure to the alternatives.     

Information limits on identification of natural surfaces by apparent colour

By adaptational and other mechanisms, the visual system can compensate for moderate changes in the colour of the illumination on a scene. Although the colours of most surfaces are perceived to be constant ('colour constancy'), some are not. The effect of these residual colour changes on the ability of observers to identify surfaces by their apparent colour was determined theoretically from high-resolution hyperspectral images of natural scenes under different daylights with correlated colour temperatures 4,300 K, 6,500 K, and 25,000 K. Perceived differences between colours were estimated with an approximately uniform colour-distance measure. The information preserved under illuminant changes increased with the number of surfaces in the sample, but was limited to a relatively low asymptotic value, indicating the importance of physical factors in constraining identification by apparent colour.     

Examining time‐invariance in reliability in multi‐wave,multi‐indicator models: A covariance structure analysis approach accounting for indicator specificity

A covariance structure analysis method for testing time‐invariance in reliability in multiwave, multiple‐indicator models in outlined. The approach accounts for observed variable specificity and permits, in addition, estimation of reliability in terms of ‘pure’ measurement error variance. The proposed procedure is developed within a confirmatory factor analysis framework and illustrated with data from a cognitive intervention study.