Local and relational judgements of surface colour: constancy indices and discrimination performance

Colour constancy is generally assumed to arise from a combination of perceptual constancy mechanisms operating to partially discount illumination changes and relational mechanisms involved in judging the colour relationships between object surfaces. Here we examined the characteristics of these mechanisms using a 'yes/no' task. Subjects judged whether a target colour patch embedded in an array of coloured patches (a) stayed the same across a simulated temporal illuminant change (local colour judgement), or (b) changed in a manner consistent with the illuminant change (relational colour judgement). The colour of the target patch remained constant in one-third of the trials, changed in accord with the illuminant shift in another third, and shifted partially with the illuminant change in the remaining third. We found that perceptual constancy was relatively weak and relational constancy strong, as assessed using a modified colour constancy index. Randomising the spatial positions of coloured patches across the illuminant change did not affect subjects' constancy indices. Application of signal detection analysis revealed some otherwise hidden effects. In the case of relational judgements, subjects adopted more conservative criteria (fewer true and false positives) with randomisation, maintaining a constant level of discrimination performance (d'). For local judgements, randomisation led to small increases in performance but no changes in criteria. We conclude that signal detection theory provides a useful tool to supplement conventional approaches to understanding colour constancy.     

Sensory, computational and cognitive components of human colour constancy

When the illumination on a scene changes, so do the visual signals elicited by that scene. In spite of these changes, the objects within a scene tend to remain constant in their apparent colour. We start this review by discussing the psychophysical procedures that have been used to quantify colour constancy. The transformation imposed on the visual signals by a change in illumination dictates what the visual system must 'undo' to achieve constancy. The problem is mathematically underdetermined, and can be solved only by exploiting regularities of the visual world. The last decade has seen a substantial increase in our knowledge of such regularities as technical advances have made it possible to make empirical measurements of large numbers of environmental scenes and illuminants. This review provides a taxonomy of models of human colour constancy based first on the assumptions they make about how the inverse transformation might be simplified, and second, on how the parameters of the inverse transformation might be set by elements of a complex scene. Candidate algorithms for human colour constancy are represented graphically and pictorially, and the availability and utility of an accurate estimate of the illuminant is discussed. Throughout this review, we consider both the information that is, in principle, available and empirical assessments of what information the visual system actually uses. In the final section we discuss where in our visual systems these computations might be implemented.     

Context-dependent memory: colour versus odour

An olfactory stimulus and a visual stimulus were employed in a context- dependent memory study using a prose passage as the to-be-remembered item. Ninety-five university students (aged 17-35 years) learned the passage of prose in the presence of one of the stimuli and were then asked to recall the passage with the original context either reinstated or not reinstated. The results revealed a significant context-dependent memory effect for the olfactory cue but not for the visual cue. They demonstrate support for the effectiveness of odours as context cues and it is suggested that context-dependent memory processes may underlie the formation and retrieval of odour-evoked autobiographical memories.      

Skin texture and colour predict perceived health in Asian faces

Facial skin texture and colour play an important role in observers' judgments of apparent health and have been linked to aspects of physiological health, including fitness, immunity and fertility. However, most studies have focused on Caucasian populations. Here, we report two studies that investigate the contribution of skin texture and colour to the apparent health of Malaysian Chinese faces. In Study 1, homogenous skin texture, as measured by wavelet analysis, was found to positively predict ratings of apparent health of Asian faces. In study 2, homogenous skin texture and increased skin yellowness positively predicted rated health of Malaysian Chinese faces. This finding suggests that skin condition serves as an important cue for subjective judgements of health in Malaysian Chinese faces.     

Conjunctions of colour, luminance and orientation: the role of colour and luminance contrast on saliency and proximity grouping in texture segregation

To examine whether perceptual grouping on the basis of orientation can be performed simultaneously with or only subsequently to grouping according to colour or luminance, we tested whether subjects are able to segregate arrays of texture elements that differ from surrounding elements by conjunctions of either (i) colour and orientation, or (ii) luminance contrast and orientation, or (iii) luminance contrast polarity and orientation. Subjects were able to use conjunctions between luminance and orientation for segregation but not conjunctions between colour or contrast polarity and orientation. Our results suggest that (i) in agreement with earlier findings, there seem to exist no specific conjunction detectors for colour and orientation or contrast polarity and orientation, and (ii) when orientation defined textures are to be distinguished by virtue of differences in luminance, colour, or contrast polarity, luminance provides a much stronger cue than colour or contrast polarity for saliency-based orientation grouping.     

Development of contrast sensitivity and acuity of the infant colour system

We have monitored the development of infant colour vision by measuring chromatic contrast sensitivity and acuity in eight young infants over a period of 6 months. Steady-state visual evoked potentials (VEPS) were recorded in response to both chromatic (red-green) and luminance (red-black or green-black) patterns that were reversed in contrast over time. For most infants, no response could be obtained to chromatic stimuli of any size or contrast before 5 weeks of age, although luminance stimuli of 20% contrast gave reliable responses at that age. When responses to chromatic stimuli first appeared, they could be obtained only with stimuli of very low spatial frequency, 20 times lower than the acuity for luminance stimuli. Both contrast sensitivity and acuity for chromatic stimuli increased steadily, more rapidly than for luminance stimuli. As the spectral selectivities of infant cones are similar to those of adults, the difference in rate of development of luminance and chromatic contrast sensitivity and acuity stimuli probably reflects neural development of the infant colour system.     

The perceived intensity of caffeine aftertaste: tasters versus nontasters

The length and intensity of the aftertaste of caffeine was measured in groups of tasters and nontasters in order to determine if any differential information could be provided by aftertaste perception. Results indicate that a period of 4 min is sufficient to see differences between tasters and nontasters, and that nontasters' aftertaste of the saturated solution is equal in intensity with tasters perception immediately after stimulus presentation, but then after approximately 1 min fade faster. Nontaster ratings for the weaker solution were lower throughout the entire time period.     

Effect of background colour on growth and adhesion strength of Ulva sporelings

This study examined the effects of a range of black, grey and white substrata on the growth and attachment strength of Ulva sporelings on glass and polydimethylsiloxane (Silastic®-T2) surfaces. The rate of development of sporelings was strongly influenced by the colour of the substratum on which they grew. On black backgrounds, sporelings grew slowly and germination was delayed. Laboratory screening methods for antifouling and fouling-release coatings that rely on the growth of Ulva sporelings can be compromised if samples are of different colours. Hydrodynamic removal of sporelings from coatings may also be affected by substratum colour, since smaller plants generate lower hydrodynamic forces making them more difficult to remove.     

Colour contrast influences perceived shape in combined shading and texture patterns

The 'colour-shading effect' describes the phenomenon whereby a chromatic pattern influences perceived shape-from-shading in a luminance pattern. Specifically, the depth corrugations perceived in sinusoidal luminance gratings can be enhanced by spatially non-aligned, and suppressed by spatially aligned sinusoidal chromatic gratings. Here we examine whether colour contrast can influence perceived shape in patterns that combine shape-from-shading with shape-from-texture. Stimuli consisted of sinusoidal modulations of texture (defined by orientation), luminance and colour. When the texture and luminance modulations were suitably combined, one obtained a vivid impression of a corrugated depth surface. The addition of a colour grating to the texture-luminance combination was found to enhance the impression of depth when out-of-phase with the luminance modulation, and suppress the impression of depth when in-phase with the luminance modulation. The degree of depth enhancement and depth suppression was approximately constant across texture amplitude when measured linearly. In the absence of the luminance grating however, the colour grating had no phase-dependent affect on perceived depth. These results show that colour contrast modulates the contribution of shading to perceived shape in combined shading and texture patterns.     

Oxygenated-blood colour change thresholds for perceived facial redness, health, and attractiveness

Blood oxygenation level is associated with cardiovascular fitness, and raising oxygenated blood colouration in human faces increases perceived health. The current study used a two-alternative forced choice (2AFC) psychophysics design to quantify the oxygenated blood colour (redness) change threshold required to affect perception of facial colour, health and attractiveness. Detection thresholds for colour judgments were lower than those for health and attractiveness, which did not differ. The results suggest redness preferences do not reflect a sensory bias, rather preferences may be based on accurate indications of health status. Furthermore, results suggest perceived health and attractiveness may be perceptually equivalent when they are assessed based on facial redness. Appearance-based motivation for lifestyle change can be effective; thus future studies could assess the degree to which cardiovascular fitness increases face redness and could quantify changes in aerobic exercise needed to increase facial attractiveness.     

Effect of background colour on growth and adhesion strength of Ulva sporelings

This study examined the effects of a range of black, grey and white substrata on the growth and attachment strength of Ulva sporelings on glass and polydimethylsiloxane (Silastic-T2) surfaces. The rate of development of sporelings was strongly influenced by the colour of the substratum on which they grew. On black backgrounds, sporelings grew slowly and germination was delayed. Laboratory screening methods for antifouling and fouling-release coatings that rely on the growth of Ulva sporelings can be compromised if samples are of different colours. Hydrodynamic removal of sporelings from coatings may also be affected by substratum colour, since smaller plants generate lower hydrodynamic forces making them more difficult to remove.     

Assessment of novel binocular colour, motion and contrast tests in glaucoma

The effects of glaucoma on binocular visual sensitivity for the detection of various stimulus attributes are investigated at the fovea and in four paracentral retinal regions. The study employed a number of visual stimuli designed to isolate the processing of various stimulus attributes. We measured absolute contrast detection thresholds and functional contrast sensitivity by using Landolt ring stimuli. This psychophysical Landolt C-based contrast test of detection and gap discrimination allowed us to test parafoveally at 6 ° from fixation and foveally by employing interleaved testing locations. First-order motion perception was examined by using moving stimuli embedded in static luminance contrast noise. Red/green (RG) and yellow/blue (YB) colour thresholds were measured with the Colour Assessment and Diagnosis (CAD) test, which utilises random dynamic luminance contrast noise (± 45 %) to ensure that only colour and not luminance signals are available for target detection. Subjects were normal controls (n?=?65) and glaucoma patients with binocular visual field defects (n?=?15) classified based on their Humphrey Field Analyzer mean deviation (MD) scores. The impairment of visual function varied depending on the stimulus attribute and location tested. Progression of loss was noted for all tests as the degree of glaucoma increased. For subjects with mild glaucoma (MD ?0.01 dB to ?6.00 dB) significantly more data points fell outside the normal age-representative range for RG colour thresholds than for any other visual test, followed by motion thresholds. This was particularly the case for the parafoveal data compared with the foveal data. Thus, a multifaceted measure of binocular visual performance, incorporating RG colour and motion test at multiple locations, might provide a better index for comparison with quality of life measures in glaucoma.     

Brightness versus apparent contrast. 2: Large-field asymmetry.

Experiments were performed on the quasi-static perception of brightness and of apparent contrast of a foveal 1-deg disk, presented either as a luminance increment or decrement against a 300 cd.m-2 background. Results suggest that the perceptual attributes of brightness and apparent (or subjective) contrast should be distinguished. For an equal brightness difference with respect to the background, luminance increments are more effective than decrements. For an equal apparent contrast it is found that increments and decrements, up to 100 cd.m-2, are about equally effective; for higher values luminance decrements are more effective. Brightness increments and decrements can both be described by a Stevens power function of the respective luminance increments and decrements. Apparent contrast can, apart from applying a usual luminance contrast formula, also be described as a power function of the luminance difference with the background.     

Effect of colour of drugs: systematic review of perceived effect of drugs and of their effectiveness.

OBJECTIVE: To assess the impact of the colour of a drug''s formulation on its perceived effect and its effectiveness and to examine whether antidepressant drugs available in the Netherlands are different in colour from hypnotic, sedative, and anxiolytic drugs. DESIGN: Systematic review of 12 published studies. Six studies examined the perceived action of different coloured drugs and six the influence of the colour of a drug on its effectiveness. The colours of samples of 49 drugs affecting the central nervous system were assessed using a colour atlas. MAIN OUTCOME MEASURES: Perceived stimulant action versus perceived depressant action of colour of drugs; the trials that assessed the effect of drugs in different colours were done in patients with different diseases and had different outcome measures. RESULTS: The studies on perceived action of coloured drugs showed that red, yellow, and orange are associated with a stimulant effect, while blue and green are related to a tranquillising effect. The trials that assessed the impact of the colour of drugs on their effectiveness showed inconsistent differences between colours. The quality of the methods of these trials was variable. Hypnotic, sedative, and anxiolytic drugs were more likely than antidepressants to be green, blue, or purple. CONCLUSIONS: Colours affect the perceived action of a drug and seem to influence the effectiveness of a drug. Moreover, a relation exists between the colouring of drugs that affect the central nervous system and the indications for which they are used. Research contributing to a better understanding of the effect of the colour of drugs is warranted.     

Long-term satellite tracking of white stork ( Ciconia ciconia) migration: constancy versus variability

During satellite-tracking investigations of 140 white storks (Ciconia ciconia), one individual, the long-term world record holder among birds, was followed along 12 migratory journeys over a period of 10 years. This long-term study confirms what previous several-year tracking studies of white storks had indicated: there can be great variability from year to year in the choice of winter quarters as well as in the routes and times of migration, intermediate destinations and stop-over periods, but constancy of winter quarters and migration routes is also possible. The variability may well be caused by external factors, of which food supply is probably predominant.Communicated by F. Bairlein     

Dual-curing resin cement with colour indicator for adhesively cemented restorations to dental tissues: Change of colour by curing and some physical properties

The study was aimed to investigate a color indicator containing dual curing resin composite luting cement and to plot the color change to the time of solidification of the cement. In addition some physical properties were studied. Specimens were made of a dual-cure resin cement (Maxcem Elite™ Chroma, Kerr, Orange, CA, USA) and polymerized by autopolymerization only, or with light initiated polymerization. A spectrophotometer was used to quantify the color change of the cement as plotted with the curing time. The efficacy of the curing process was studied by measuring water sorption and the ultimate flexural properties of the cement. The results showed that the flexural strength of cement after autopolymerization was 27.3 MPa and after light initiated polymerization 48.1 MPa. Young’s modulus of bending was 2089.3 MPa and 3781.5 MPa respectively for the same cement samples. Water sorption after two weeks for the autopolymerization cement samples was −1.12 wt% and for the light initiated polymerization samples 0.56 wt%. Non-parametric Spearman’s correlation was measured for autopolymerized cement samples between variables for color and solidification load (N), which showed a strong correlation between curing process and color change (p < 0.05). There was a correlation between the color change and degree of monomer conversion of the dual curing resin composite luting cement which contained a color indicator system for polymerization reaction. The study also suggested that autopolymerization only resulted in suboptimal polymerization of the cement. By additional light curing considerably higher flexural properties were obtained.     

Effects of lifestyle physical activity on perceived symptoms and physical function in adults with fibromyalgia: results of a randomized trial

Introduction  

Although exercise is therapeutic for adults with fibromyalgia (FM), its symptoms often create obstacles that discourage exercise. We evaluated the effects of accumulating at least 30 minutes of self-selected lifestyle physical activity (LPA) on perceived physical function, pain, fatigue, body mass index, depression, tenderness, and the six-minute walk test in adults with FM.